In their studies on the molecular basis of osteopoikilosis, Menten et al have identified three individuals with microdeletions on chromosome 12q14.4, which removed several genes including LEMD3, the osteopoikilosis gene. In addition to osteopoikilosis, affected individuals had growth retardation and developmental delay. We now report a smaller 12q14.4 microdeletion in a boy with severe pre and postnatal growth failure, and mild developmental delay; the patient was small at birth and presented with poor feeding and failure to thrive during the first 2 years of life, similar to the phenotype of primordial dwarfism or severe Silver-Russell syndrome (SRS). The 12q14 deletion did not include LEMD3, and no signs of osteopoikilosis were observed on skeletal radiographs. Among the deleted genes, HMGA2 is of particular interest in relationship to the aberrant somatic growth in our patient, as HMGA2 variants have been linked to stature variations in the general population and loss of function of Hmga2 in the mouse results in the pygmy phenotype that combines pre and postnatal growth failure, with resistance to the adipogenic effect of overfeeding. Sequencing of the remaining HMGA2 allele in our patient showed a normal sequence, suggesting that HMGA2 haploinsufficiency may be sufficient to produce the aberrant growth phenotype. We conclude that the 12q14.4 microdeletion syndrome can occur with or without deletion of LEMD3 gene; in LEMD3-intact cases, the phenotype includes primordial short stature and failure to thrive with moderate developmental delay, but osteopoikilosis is absent. Such cases will likely be diagnosed as Silver-Russell-like or as primordial dwarfism.
HMGA2; silver-russell phenotype; primordial dwarfism; 12q14 microdeletion; array-CGH
Osteopoikilosis is a rare autosomal dominant genetic disorder, characterised by the occurrence of the hyperostotic spots preferentially localized in the epiphyses and metaphyses of the long bones, and in the carpal and tarsal bones . Heterozygous LEMD3 gene mutations were shown to be the primary cause of the disease . Association of the primarily asymptomatic osteopokilosis with connective tissue nevi of the skin is categorized as Buschke-Ollendorff syndrome (BOS) . Additionally, osteopoikilosis can coincide with melorheostosis (MRO), a more severe bone disease characterised by the ectopic bone formation on the periosteal and endosteal surface of the long bones [4-6]. However, not all MRO affected individuals carry germ-line LEMD3 mutations . Thus, the genetic cause of MRO remains unknown. Here we describe a familial case of osteopoikilosis in which a novel heterozygous LEMD3 mutation coincides with a novel mutation in EXT1, a gene involved in aetiology of multiple exostosis syndrome. The patients affected with both LEMD3 and EXT1 gene mutations displayed typical features of the osteopoikilosis. There were no additional skeletal manifestations detected however, various non-skeletal pathologies coincided in this group.
We investigated LEMD3 and EXT1 in the three-generation family from Poland, with 5 patients affected with osteopoikilosis and one child affected with multiple exostoses.
We found a novel c.2203C > T (p.R735X) mutation in exon 9 of LEMD3, resulting in a premature stop codon at amino acid position 735. The mutation co-segregates with the osteopoikilosis phenotype and was not found in 200 ethnically matched controls. Another new substitution G > A was found in EXT1 gene at position 1732 (cDNA) in Exon 9 (p.A578T) in three out of five osteopoikilosis affected family members. Evolutionary conservation of the affected amino acid suggested possible functional relevance, however no additional skeletal manifestations were observed other then those specific for osteopoikilosis. Finally in one member of the family we found a splice site mutation in the EXT1 gene intron 5 (IVS5-2 A > G) resulting in the deletion of 9 bp of cDNA encoding three evolutionarily conserved amino acid residues. This child patient suffered from a severe form of exostoses, thus a causal relationship can be postulated.
We identified a new mutation in LEMD3 gene, accounting for the familial case of osteopoikilosis. In the same family we identified two novel EXT1 gene mutations. One of them A598T co-incided with the LEMD3 mutation. Co-incidence of LEMD3 and EXT1 gene mutations was not associated with a more severe skeletal phenotype in those patients.
Genomic disorders are often caused by non-allelic homologous recombination between segmental duplications. Chromosome 16 is especially rich in a chromosome-specific low copy repeat, termed LCR16.
Methods and Results:
A bacterial artificial chromosome (BAC) array comparative genome hybridisation (CGH) screen of 1027 patients with mental retardation and/or multiple congenital anomalies (MR/MCA) was performed. The BAC array CGH screen identified five patients with deletions and five with apparently reciprocal duplications of 16p13 covering 1.65 Mb, including 15 RefSeq genes. In addition, three atypical rearrangements overlapping or flanking this region were found. Fine mapping by high-resolution oligonucleotide arrays suggests that these deletions and duplications result from non-allelic homologous recombination (NAHR) between distinct LCR16 subunits with >99% sequence identity. Deletions and duplications were either de novo or inherited from unaffected parents. To determine whether these imbalances are associated with the MR/MCA phenotype or whether they might be benign variants, a population of 2014 normal controls was screened. The absence of deletions in the control population showed that 16p13.11 deletions are significantly associated with MR/MCA (p = 0.0048). Despite phenotypic variability, common features were identified: three patients with deletions presented with MR, microcephaly and epilepsy (two of these had also short stature), and two other deletion carriers ascertained prenatally presented with cleft lip and midline defects. In contrast to its previous association with autism, the duplication seems to be a common variant in the population (5/1682, 0.29%).
These findings indicate that deletions inherited from clinically normal parents are likely to be causal for the patients’ phenotype whereas the role of duplications (de novo or inherited) in the phenotype remains uncertain. This difference in knowledge regarding the clinical relevance of the deletion and the duplication causes a paradigm shift in (cyto)genetic counselling.
Non-allelic homologous recombination (NAHR) between segmental duplications in proximal chromosome 15q breakpoint (BP) regions can lead to microdeletions and microduplications. Several individuals with deletions flanked by BP3 and BP4 on 15q13, immediately distal to, and not including the Prader–Willi/Angelman syndrome (PW/AS) critical region and proximal to the BP4–BP5 15q13.3 microdeletion syndrome region, have been reported; however, because the deletion has also been found in normal relatives, the significance of these alterations is unclear. We have identified six individuals with deletions limited to the BP3–BP4 interval and an additional four individuals with deletions of the BP3–BP5 interval from 34 046 samples submitted for clinical testing by microarray-based comparative genomic hybridization (aCGH). Of four individuals with BP3–BP4 deletions for whom parental testing was conducted, two were apparently de novo and two were maternally inherited. A comparison of clinical features, available for five individuals in our study (four with deletions within BP3–BP4 and one with a BP3-BP5 deletion), with those in the literature show common features of short stature and/or failure to thrive, microcephaly, hypotonia, and premature breast development in some individuals. Although the BP3–BP4 deletion does not yet demonstrate statistically significant enrichment in abnormal populations compared with control populations, the presence of common clinical features among probands and the presence of genes with roles in development and nervous system function in the deletion region suggest that this deletion may have a role in abnormal phenotypes in some individuals.
15q13; segmental duplication; microdeletion; genotype–phenotype
Microdeletions in 16q24.3 are associated with intellectual disability and a specific phenotype, e.g. short stature and a prominent forehead. The 16q24.3 microdeletion syndrome shows a broad phenotypic overlap with the KBG syndrome, which is caused by mutations within the ANKRD11 gene. Furthermore, both KBG and the 16q24.3 microdeletion syndromes show clinical findings reminiscent of Silver-Russell syndrome (SRS), an imprinting disorder characterized by severe primordial growth retardation. In a cohort of patients referred as SRS, we previously identified a 16q24.3 deletion, but at that time, only patients with larger imbalances in 16q24.3 and intellectual disability had been published. Considering the recent description of the ANKRD11 gene as the causative factor for the 2 16q24.3-associated disorders, we now classified our patient as a 16q24.3 microdeletion syndrome patient exhibiting some characteristic features but normal intelligence. Our case illustrates the broad clinical spectrum associated with microdeletions, and we confirm that the 16q24.3 microdeletion syndrome is a further microdeletion syndrome with very variable expressivity. Indeed, our case is the first 16q24.3 patient of normal intelligence, but we assume that this variant is present in further mentally healthy probands which have not yet been tested. In conclusion, the detection of the 16q24.3 deletion in a proband of unremarkable intellectual capacities once again illustrates the need to perform molecular karyotyping in dysmorphic patients with normal intelligence.
ANKRD11 gene; KBG syndrome; Molecular karyotyping; 16q24.3 microdeletion; Silver-Russell syndrome
Human growth has an estimated heritability of about 80%–90%. Nevertheless, the underlying cause of shortness of stature remains unknown in the majority of individuals. Genome-wide association studies (GWAS) showed that both common single nucleotide polymorphisms and copy number variants (CNVs) contribute to height variation under a polygenic model, although explaining only a small fraction of overall genetic variability in the general population. Under the hypothesis that severe forms of growth retardation might also be caused by major gene effects, we searched for rare CNVs in 200 families, 92 sporadic and 108 familial, with idiopathic short stature compared to 820 control individuals. Although similar in number, patients had overall significantly larger CNVs (p-value<1×10−7). In a gene-based analysis of all non-polymorphic CNVs>50 kb for gene function, tissue expression, and murine knock-out phenotypes, we identified 10 duplications and 10 deletions ranging in size from 109 kb to 14 Mb, of which 7 were de novo (p<0.03) and 13 inherited from the likewise affected parent but absent in controls. Patients with these likely disease causing 20 CNVs were smaller than the remaining group (p<0.01). Eleven (55%) of these CNVs either overlapped with known microaberration syndromes associated with short stature or contained GWAS loci for height. Haploinsufficiency (HI) score and further expression profiling suggested dosage sensitivity of major growth-related genes at these loci. Overall 10% of patients carried a disease-causing CNV indicating that, like in neurodevelopmental disorders, rare CNVs are a frequent cause of severe growth retardation.
With a frequency of 3%, shortness of stature is a common medical concern. Although family studies have clearly shown that gene defects play a pivotal role in the development of short stature, the underlying genetic variants involved remain unknown in about 80% of cases. In contrast to recent studies which aimed at the identification of common genetic variants to explain minor differences in the height variation in the general population, we targeted rare genomic variants where we expected a major gene effect on growth. By examining 200 patients clinically evaluated for short stature, we show that rare structural chromosomal aberrations (CNVs) are associated with shortness of stature in 10% of the cases. The identified CNVs were either de novo or segregated with short stature in the families and include genes that are functionally involved in growth regulation in humans or mice. We furthermore demonstrate an overlap of these CNVs with known microdeletion syndromes. Interestingly, 3 CNVs contain positions of common variants and confirm the localization of major growth-related genes. These findings are particularly important for identification of biological pathways leading to short stature, but also for further therapeutic approaches.
Prader-Willi syndrome (PWS [MIM 176270]) is a neurogenetic disorder characterized by decreased fetal activity, muscular hypotonia, failure to thrive, short stature, obesity, mental retardation, and hypogonadotropic hypogonadism. It is caused by the loss of function of one or more imprinted, paternally expressed genes on the proximal long arm of chromosome 15. Several potential PWS mouse models involving the orthologous region on chromosome 7C exist. Based on the analysis of deletions in the mouse and gene expression in PWS patients with chromosomal translocations, a critical region (PWScr) for neonatal lethality, failure to thrive, and growth retardation was narrowed to the locus containing a cluster of neuronally expressed MBII-85 small nucleolar RNA (snoRNA) genes. Here, we report the deletion of PWScr. Mice carrying the maternally inherited allele (PWScrm−/p+) are indistinguishable from wild-type littermates. All those with the paternally inherited allele (PWScrm+/p−) consistently display postnatal growth retardation, with about 15% postnatal lethality in C57BL/6, but not FVB/N crosses. This is the first example in a multicellular organism of genetic deletion of a C/D box snoRNA gene resulting in a pronounced phenotype.
Prader-Willi syndrome, or PWS, is a complex neurogenetic disorder and the most common genetic cause of life-threatening childhood obesity. Newborns have poor muscle tone, making suckling difficult, which leads to poor weight gain. After infancy, they experience extreme hunger, leading to obesity. Other symptoms include short stature, mental retardation, and often infertility. In PWS patients, a complex set of genes on the paternal chromosome 15 (in the PWS region) is missing or unexpressed. In an attempt to understand this disorder, various protein-coding genes in this region have been deleted in mice, but none of the resulting phenotypes consistently correlated with the human disease. This region also contains a cluster of genes that encode functional non-protein-coding RNAs. We deleted specifically the MBII-85 small nucleolar RNA (snoRNA) gene cluster on the parental mouse chromosome, which did not affect expression of any of the other snoRNA or protein-coding genes in the PWS region. These mice consistently displayed postnatal growth retardation starting from day 5 to 6, low postnatal lethality only in certain genetic backgrounds (<15%), and no adolescent obesity. Thus, this mouse model, with the deletion of a small, brain-specific non-protein-coding RNA, should prove useful for teasing out the various molecular pathologies of PWS.
We report four new patients with a submicroscopic deletion in 15q24 manifesting developmental delay, short stature, hypotonia, digital abnormalities, joint laxity, genital abnormalities, and characteristic facial features. These clinical features are shared with six recently reported patients with a 15q24 microdeletion, supporting the notion that this is a recognizable syndrome. We describe a case of an ~2.6 Mb microduplication involving a portion of the minimal deletion critical region in a 15-year-old male with short stature, mild mental retardation, attention deficit hyperactivity disorder, Asperger syndrome, decreased joint mobility, digital abnormalities, and characteristic facial features. Some of these features are shared with a recently reported case with a 15q24 microduplication involving the minimal deletion critical region. We also report two siblings and their mother with duplication adjacent and distal to this region exhibiting mild developmental delay, hypotonia, tapering fingers, characteristic facial features, and prominent ears. The deletion and duplication breakpoints were mapped by array comparative genomic hybridization and the genomic structure in 15q24 was analyzed further. Surprisingly, in addition to the previously recognized three low-copy repeat clusters (BP1, BP2, and BP3), we identified two other paralogous low-copy repeat clusters that likely mediated the formation of alternative sized 15q24 genomic rearrangements via non-allelic homologous recombination.
Microdeletions including 5q31 have been reported in only few patients to date. Apart from intellectual disability/developmental delay (ID/DD) of varying degrees, which is common to all reported patients, the clinical spectrum is wide and includes short stature, failure to thrive, congenital heart defects, encephalopathies, and dysmorphic features. We report a patient with a 0.9-Mb de novo deletion in 5q31.2, the smallest microdeletion in 5q31 reported thus far. His clinical presentation includes mild DD, borderline short stature, postnatal microcephaly, and mild dysmorphic signs including microretrognathia. Together with data from 7 reported overlapping microdeletions, analysis of our patient enabled the tentative delineation of a phenotype map for 5q31 deletions. In contrast to the mild phenotype of small microdeletions affecting only 5q31.2, carriers of larger microdeletions which also include subbands 5q31.1 and/or 5q31.3 seem to be more severely affected with congenital malformations, growth anomalies, and severe encephalopathies. A 240-kb smallest region of overlap in 5q31.2 is delineated which contains only 2 genes, CTNNA1 and LRRTM2. We propose LRRTM2 as the most promising candidate gene for ID/DD due to its expression pattern, function as a key regulator of excitatory development, and interaction with Neurexin 1. However, sequence analysis of LRRTM2 in 330 patients with ID/DD revealed no relevant alterations, excluding point mutations in LRRTM2 as a frequent cause of ID/DD in patients without microdeletions.
Candidate gene; Developmental delay; Intellectual disability; LRRTM2; Microdeletion; Molecular karyotyping; 5q31.2
Six submicroscopic deletions comprising chromosome band 2q23.1 in patients with severe mental retardation (MR), short stature, microcephaly and epilepsy have been reported, suggesting that haploinsufficiency of one or more genes in the 2q23.1 region might be responsible for the common phenotypic features in these patients. In this study, we report the molecular and clinical characterisation of nine new 2q23.1 deletion patients and a clinical update on two previously reported patients. All patients were mentally retarded with pronounced speech delay and additional abnormalities including short stature, seizures, microcephaly and coarse facies. The majority of cases presented with stereotypic repetitive behaviour, a disturbed sleep pattern and a broad-based gait. These features led to the initial clinical impression of Angelman, Rett or Smith–Magenis syndromes in several patients. The overlapping 2q23.1 deletion region in all 15 patients comprises only one gene, namely, MBD5. Interestingly, MBD5 is a member of the methyl CpG-binding domain protein family, which also comprises MECP2, mutated in Rett's syndrome. Another gene in the 2q23.1 region, EPC2, was deleted in 12 patients who had a broader phenotype than those with a deletion of MBD5 only. EPC2 is a member of the polycomb protein family, involved in heterochromatin formation and might be involved in causing MR. Patients with a 2q23.1 microdeletion present with a variable phenotype and the diagnosis should be considered in mentally retarded children with coarse facies, seizures, disturbed sleeping patterns and additional specific behavioural problems.
2q23.1; Angelman; EPC2; MBD5; microdeletion; Rett
Interstitial deletions of 3q29 have been recently described as a microdeletion syndrome mediated by nonallelic homologous recombination between low-copy repeats resulting in an ~1.6 Mb common-sized deletion. Given the molecular mechanism causing the deletion, the reciprocal duplication is anticipated to occur with equal frequency, although only one family with this duplication has been reported.
In this study we describe 14 individuals with microdeletions of 3q29, including one family with a mildly affected mother and two affected children, identified among 14,698 individuals with idiopathic mental retardation who were analyzed by array CGH. Eleven individuals had typical 1.6-Mb deletions. Three individuals had deletions that flank, span, or partially overlap the commonly deleted region. Although the clinical presentations of individuals with typical-sized deletions varied, several features were present in multiple individuals, including mental retardation and microcephaly. We also identified 19 individuals with duplications of 3q29, five of which appear to be the reciprocal duplication product of the 3q29 microdeletion and 14 of which flank, span, or partially overlap the common deletion region. The clinical features of individuals with microduplications of 3q29 also varied with few common features. De novo and inherited abnormalities were found in both the microdeletion and microduplication cohorts illustrating the need for parental samples to fully characterize these abnormalities.
Our report demonstrates that array CGH is especially suited to identify chromosome abnormalities with unclear or variable presentations.
In a 2 and a half-year-old girl with onset of puberty before the age of 5 months, short stature, hand anomalies and severe mental retardation, an 8.9 Mb interstitial 19p13 duplication containing 215 predicted genes was detected. It was initially assumed that the duplication involved the kisspeptin receptor gene, GPR54, known to stimulate induction of puberty, but more refined duplication mapping excluded this possibility. In an attempt to further understand the genotype–phenotype correlation, global gene expression was measured in skin fibroblasts. The overall expression pattern was quite similar to controls, and only about 25% of the duplicated genes had an expression level that was increased by more than 1.3-fold, with no obvious changes that could explain the precocious puberty. The proband's mother carried a balanced between-arm insertion of the duplicated segment that resembled a pericentric inversion. The same insertion was found in several other family members, including one who had lost a daughter with severe mental retardation and menarche at the age of 10 years. Another close relative was severely mentally retarded, but neither dysmorphic nor microcephalic. His phenotype was initially ascribed to a presumed cryptic chromosome 19 imbalance caused by the 19p-into19q insertion, but subsequent array-CGH detected a 3.9-Mb deletion of 2q23.3q24.1. This novel microdeletion involves seven genes, of which FMNL2, a suggested regulator of Rho-GTPases, and NR4A2, an essential gene for differentiation of dopaminergic neurons, may be critical genes for the proposed 2q23q24 microdeletion syndrome.
intrachromosomal insertion; 19p13 duplication; 2q23.3 deletion; 2q24.1 deletion; precocious puberty; NR4A2; FMNL2
Recent molecular cytogenetic data have shown that the constitution of complex chromosome rearrangements (CCRs) may be more complicated than previously thought. The complicated nature of these rearrangements challenges the accurate delineation of the chromosomal breakpoints and mechanisms involved. Here, we report a molecular cytogenetic analysis of two patients with congenital anomalies and unbalanced de novo CCRs involving chromosome 17p using high-resolution array-based comparative genomic hybridization (array CGH) and fluorescent in situ hybridization (FISH). In the first patient, a 4-month-old boy with developmental delay, hypotonia, growth retardation, coronal synostosis, mild hypertelorism, and bilateral club feet, we found a duplication of the Charcot-Marie–Tooth disease type 1A and Smith-Magenis syndrome (SMS) chromosome regions, inverted insertion of the Miller-Dieker lissencephaly syndrome region into the SMS region, and two microdeletions including a terminal deletion of 17p. The latter, together with a duplication of 21q22.3-qter detected by array CGH, are likely the unbalanced product of a translocation t(17;21)(p13.3;q22.3). In the second patient, an 8-year-old girl with mental retardation, short stature, microcephaly and mild dysmorphic features, we identified four submicroscopic interspersed 17p duplications. All 17 breakpoints were examined in detail by FISH analysis. We found that four of the breakpoints mapped within known low-copy repeats (LCRs), including LCR17pA, middle SMS-REP/LCR17pB block, and LCR17pC. Our findings suggest that the LCR burden in proximal 17p may have stimulated the formation of these CCRs and, thus, that genome architectural features such as LCRs may have been instrumental in the generation of these CCRs.
It has previously been shown that specific microdeletions and microduplications, many of which also associated with cognitive impairment (CI), can present with autism spectrum disorders (ASDs). Multiplex ligation-dependent probe amplification (MLPA) represents an efficient method to screen for such recurrent microdeletions and microduplications.
In the current study, a total of 279 unrelated subjects ascertained for ASDs were screened for genomic disorders associated with CI using MLPA. Fluorescence in situ hybridization (FISH), quantitative polymerase chain reaction (Q-PCR) and/or direct DNA sequencing were used to validate potential microdeletions and microduplications. Methylation-sensitive MLPA was used to characterize individuals with duplications in the Prader-Willi/Angelman (PWA) region.
MLPA showed two subjects with typical ASD-associated interstitial duplications of the 15q11-q13 PWA region of maternal origin. Two additional subjects showed smaller, de novo duplications of the PWA region that had not been previously characterized. Genes in these two novel duplications include GABRB3 and ATP10A in one case, and MKRN3, MAGEL2 and NDN in the other. In addition, two subjects showed duplications of the 22q11/DiGeorge syndrome region. One individual was found to carry a 12 kb deletion in one copy of the ASPA gene on 17p13, which when mutated in both alleles leads to Canavan disease. Two subjects showed partial duplication of the TM4SF2 gene on Xp11.4, previously implicated in X-linked non-specific mental retardation, but in our subsequent analyses such variants were also found in controls. A partial duplication in the ASMT gene, located in the pseudoautosomal region 1 (PAR1) of the sex chromosomes and previously suggested to be involved in ASD susceptibility, was observed in 6–7% of the cases but in only 2% of controls (P = 0.003).
MLPA proves to be an efficient method to screen for chromosomal abnormalities. We identified duplications in 15q11-q13 and in 22q11, including new de novo small duplications, as likely contributing to ASD in the current sample by increasing liability and/or exacerbating symptoms. Our data indicate that duplications in TM4SF2 are not associated with the phenotype given their presence in controls. The results in PAR1/PAR2 are the first large-scale studies of gene dosage in these regions, and the findings at the ASMT locus indicate that further studies of the duplication of the ASMT gene are needed in order to gain insight into its potential involvement in ASD. Our studies also identify some limitations of MLPA, where single base changes in probe binding sequences alter results. In summary, our studies indicate that MLPA, with a focus on accepted medical genetic conditions, may be an inexpensive method for detection of microdeletions and microduplications in ASD patients for purposes of genetic counselling if MLPA-identified deletions are validated by additional methods.
Recently the genotype/phenotype map of Wolf‐Hirschhorn syndrome (WHS) has been refined, using small 4p deletions covering or flanking the critical region in patients showing only some of the WHS malformations. Accordingly, prenatal‐onset growth retardation and failure to thrive have been found to result from haploinsufficiency for a 4p gene located between 0.4 and 1.3 Mb, whereas microcephaly results from haploinsufficiency of at least two different 4p regions, one of 2.2–2.38 Mb and a second one of 1.9–1.28 Mb.
Methods and Results
We defined the deletion size of a ring chromosome (r(4)) in a girl with prenatal onset growth retardation, severe failure to thrive and true microcephaly but without the WHS facial gestalt and mental retardation. A high‐resolution comparative genome hybridisation array revealed a 760 kb 4p terminal deletion.
This case, together with a familial 4p deletion involving the distal 400 kb reported in normal women, may narrow the critical region for short stature on 4p to 360–760 kb. This region is also likely to contain a gene for microcephaly. “In silico” analysis of all genes within the critical region failed to reveal any strikingly suggestive expression pattern; all genes remain candidates for short stature and microcephaly.
The emerging 3q13.31 microdeletion syndrome appears to encompass diverse neurodevelopmental conditions. However, the 3q13.31 deletion is rare and few adult cases have yet been reported. We examined a cohort with schizophrenia (n = 459) and adult control subjects (n = 26,826) using high-resolution microarray technology for deletions and duplications at the 3q13.31 locus.
We report on the extended adult phenotype associated with a 3q13.31 microdeletion in a 41-year-old male proband with schizophrenia and a nonverbal learning disability. He was noted to have a speech impairment, delayed motor skills, and other features consistent with the 3q13.31 microdeletion syndrome. The 2.06 Mb deletion overlapped two microRNAs and seven RefSeq genes, including GAP43, LSAMP, DRD3, and ZBTB20. No overlapping 3q13.31 deletions or duplications were identified in control subjects.
Later-onset conditions like schizophrenia are increasingly associated with rare copy number variations and associated genomic disorders like the 3q13.31 microdeletion syndrome. Detailed phenotype information across the lifespan facilitates genotype-phenotype correlations, accurate genetic counselling, and anticipatory care.
3q13 deletion; Schizophrenia; Copy number variation; Genotype-phenotype correlation; Genetic counselling; Genomic disorder; Nonverbal learning disability
We report six patients with array deletions encompassing 12q14. Out of a total of 2538 array investigations carried out on children with developmental delay and dysmorphism in three diagnostic testing centres, six positive cases yielded a frequency of 1 in 423 for this deletion syndrome. The deleted region in each of the six cases overlaps significantly with previously reported cases with microdeletions of this region. The chromosomal range of the deletions extends from 12q13.3q15. In the current study, we report overlapping deletions of variable extent and size but primarily comprising chromosomal bands 12q13.3q14.1. Four of the six deletions were confirmed as de novo events. Two cases had deletions that included HMGA2, and both children had significant short stature. Neither case had osteopoikilosis despite both being deleted for LEMD3. Four cases had deletions that ended proximal to HMGA2 and all of these had much better growth. Five cases had congenital heart defects, including two with atrial septal defects, one each with pulmonary stenosis, sub-aortic stenosis and a patent ductus. Four cases had moderate delay, two had severe developmental delay and a further two had a diagnosis of autism. All six cases had significant speech delay with subtle facial dysmorphism.
12q14 microdeletion; array-CGH; HMGA2; short stature
Normal development of the genitourinary (GU) tract is a complex process that frequently goes awry. In male children the most frequent congenital GU anomalies are cryptorchidism (1–4%), hypospadias (1%) and micropenis (0.35%). Bladder exstrophy and epispadias complex (BEEC) (1∶47000) occurs less frequently but significantly impacts patients' lives. Array comparative genomic hybridization (aCGH) identified seven individuals with overlapping deletions in the 2p15 region (66.0 kb-5.6 Mb). Six of these patients have GU defects, while the remaining patient has no GU defect. These deletions encompass the transcription factor OTX1. Subjects 2–7 had large de novo CNVs (2.39–6.31 Mb) and exhibited features similar to those associated with the 2p15p16.1 and 2p15p14 microdeletion syndromes, including developmental delay, short stature, and variable GU defects. Subject-1 with BEEC had the smallest deletion (66 kb), which deleted only one copy of OTX1. Otx1-null mice have seizures, prepubescent transient growth retardation and gonadal defects. Two subjects have short stature, two have seizures, and six have GU defects, mainly affecting the external genitalia. The presence of GU defects in six patients in our cohort and eight of thirteen patients reported with deletions within 2p14p16.1 (two with deletion of OTX1) suggest that genes in 2p15 are important for GU development. Genitalia defects in these patients could result from the effect of OTX1 on pituitary hormone secretion or on the regulation of SHH signaling, which is crucial for development of the bladder and genitalia.
Recurrent 15q13.3 microdeletions were recently identified with identical proximal (BP4) and distal (BP5) breakpoints and associated with mild to moderate mental retardation and epilepsy.
To further assess the clinical implications of this novel 15q13.3 microdeletion syndrome, eighteen new probands with a deletion were molecularly and clinically characterised. In addition, we evaluated the characteristics of a family with a more proximal deletion between BP3 and BP4. Finally, four patients with a duplication in the BP3-BP4-BP5 region were included in this study to ascertain the clinical significance of duplications in this region.
The 15q13.3 microdeletion in our series was associated with a highly variable intra- and inter-familial phenotype. At least 11 of the 18 deletions identified were inherited. Moreover, 7 of 10 siblings from four different families also had this deletion: one had a mild developmental delay, four had only learning problems during childhood, but functioned well in daily life as adults, whereas the other two had no learning problems at all. In contrast to previous findings, seizures were not a common feature in our series (only 2 of 17 living probands). Three patients with deletions had cardiac defects and deletion of the KLF13 gene, located in the critical region, may contribute to these abnormalities. The limited data from the single family with the more proximal BP3-BP4 deletion suggest this deletion may have little clinical significance. Patients with duplications of the BP3-BP4-BP5 region did not share a recognizable phenotype, but psychiatric disease was noted in 2 of 4 patients.
Overall, our findings broaden the phenotypic spectrum associated with 15q13.3 deletions and suggest that, in some individuals, deletion of 15q13.3 is not sufficient to cause disease. The existence of microdeletion syndromes, associated with an unpredictable and variable phenotypic outcome, will pose the clinician with diagnostic difficulties and challenge the commonly used paradigm in the diagnostic setting that aberrations inherited from a phenotypically normal parent are usually without clinical consequences.
15q13.3; KLF13; CHRNA7; epilepsy; cardiac
Molecular karyotyping is being increasingly applied to delineate novel disease causing microaberrations and related syndromes in patients with mental retardation of unknown aetiology. We report on three unrelated patients with overlapping de novo interstitial microdeletions involving 5q14.3-q15. All three patients presented with severe psychomotor retardation, epilepsy or febrile seizures, muscular hypotonia and variable brain and minor anomalies. Molecular karyotyping revealed three overlapping microdeletions measuring 5.7, 3.9 and 3.6 Mb, respectively. The microdeletions were identified using single nucleotide polymorphism (SNP) arrays (Affymetrix 100K and Illumina 550K) and array comparative genomic hybridization (1 Mb Sanger array-CGH). Confirmation and segregation studies were performed using fluorescence in situ hybridization (FISH) and quantitative PCR. All three aberrations were confirmed and proven to have occurred de novo. The boundaries and sizes of the deletions in the three patients were different, but an overlapping region of around 1.6 Mb in 5q14.3 was defined. It included five genes: CETN3, AC093510.2, POLR3G, LYSMD3 and the proximal part of GPR98/MASS1, a known epilepsy gene. Haploinsufficiency of GPR98/MASS1 is probably responsible for the seizure phenotype in our patients. At least one other gene contained in the commonly deleted region, LYSMD3, shows a high level of central nervous expression during embryogenesis and is also, therefore, a good candidate gene for other central nervous system (CNS) symptoms, such as psychomotor retardation, brain anomalies and muscular hypotonia of the 5q14.3 microdeletion syndrome.
microdeletion 5q14.3; mental retardation; seizures; brain anomalies; molecular karyotyping
Background: Smith–Magenis syndrome (SMS) (OMIM No 182290) is a mental retardation syndrome characterised by behavioural abnormalities, including self injurious behaviours, sleep disturbance, and distinct craniofacial and skeletal anomalies. It is usually associated with deletion involving 17p11.2 and is estimated to occur in 1/25 000 births. Heterozygous frameshift mutations leading to protein truncation in retinoic acid induced 1 gene (RAI1) have been identified in individuals with phenotypic features consistent with SMS. RAI1 lies within the 17p11.2 locus, but these patients did not have 17p11.2 deletions.
Objective: Analysis of four individuals with features consistent with SMS for variations in RAI1, using a polymerase chain reaction and sequencing strategy. None of these patients carry 17p11.2 deletions.
Results: Two patients had small deletions in RAI1 resulting in frameshift and premature truncation of the protein. Missense mutations were identified in the other two. Orthologs across other genomes showed that these missense mutations occurred in identically conserved regions of the gene. The mutations were de novo, as all parental samples were normal. Several polymorphisms were also observed, including new and reported SNPs. The patients' clinical features differed from those found in 17p11.2 deletion by general absence of short stature and lack of visceral anomalies. All four patients had developmental delay, reduced motor and cognitive skills, craniofacial and behavioural anomalies, and sleep disturbance. Seizures, not previously thought to be associated with RAI1 mutations, were observed in one patient of the cohort.
Conclusions: Haploinsufficiency of the RAI1 gene is associated with most features of SMS, including craniofacial, behavioural, and neurological signs and symptoms.
Duplications and deletions in the human genome can cause disease or predispose persons to disease. Advances in technologies to detect these changes allow for the routine identification of submicroscopic imbalances in large numbers of patients.
We tested for the presence of microdeletions and microduplications at a specific region of chromosome 1q21.1 in two groups of patients with unexplained mental retardation, autism, or congenital anomalies and in unaffected persons.
We identified 25 persons with a recurrent 1.35-Mb deletion within 1q21.1 from screening 5218 patients. The microdeletions had arisen de novo in eight patients, were inherited from a mildly affected parent in three patients, were inherited from an apparently unaffected parent in six patients, and were of unknown inheritance in eight patients. The deletion was absent in a series of 4737 control persons (P = 1.1×10−7). We found considerable variability in the level of phenotypic expression of the microdeletion; phenotypes included mild-to-moderate mental retardation, microcephaly, cardiac abnormalities, and cataracts. The reciprocal duplication was enriched in the nine children with mental retardation or autism spectrum disorder and other variable features (P = 0.02). We identified three deletions and three duplications of the 1q21.1 region in an independent sample of 788 patients with mental retardation and congenital anomalies.
We have identified recurrent molecular lesions that elude syndromic classification and whose disease manifestations must be considered in a broader context of development as opposed to being assigned to a specific disease. Clinical diagnosis in patients with these lesions may be most readily achieved on the basis of genotype rather than phenotype.
Except for terminal deletions that lead to Jacobsen syndrome, interstitial deletions involving the long arm of chromosome 11 are not frequently reported. A clinically distinct phenotype is usually observed in these cases, and no clear genotype-phenotype correlation is proposed.
Here we present a case study of a 5-year-old girl with de novo submicroscopic deletion of chromosome 11q22.3 with mild mental retardation and facial dysmorphism. A standard cytogenetic analysis did not reveal any structural aberrations. In contrary, array-CGH analysis indicated a small deletion of 11q22.3.
To our knowledge, this is the smallest 11q22.3 deletion reported in literature, containing nine RefSeq genes. Although none of the deleted genes are obvious candidates for the features observed in our patient, genes CUL5 and SLN could play a key role in the features described.
11q22.3 deletion; mild mental retardation; facial dysmorphism
There are a number of reports of interstitial deletions of the long arm of chromosome 6 that have developmental delay and obesity suggesting that this is a distinct phenotype almost like Prader-Willi syndrome. Here we report a patient with a similar deletion but a strikingly different phenotype, one more in keeping with Marfan syndrome, although he does not fulfil the criteria for that syndrome. Array comparative genomic hybridization was performed to investigate a patient with a striking phenotype. This revealed an interstitial deletion of 6q14.1q15. Parental FISH studies were normal, indicating that this is a de novo deletion. Our patient has a completely different phenotype compared to other patients reported to have similar deletions. The common feature is developmental delay, but the body features are quite different in that our patient is tall, strikingly thin with pectus excavatum, scoliosis, skin striae, arachnodactyly, pes planus, cataracts, and a high-arched palate. This contrasts with other patients who have a similar deletion but have short stature and obesity. 6q14.1q15 interstitial deletions can have a very variable phenotype and do not necessarily conform to a clinical recognizable microdeletion syndrome caused by haploinsufficiency of dosage-sensitive genes in that region as proposed by others.
6q deletion; Developmental delay; Marfanoid phenotype; Mental retardation; Tall stature
Mutations and deletions of the homeobox transcription factor gene SHOX are known to cause short stature. The authors have analysed SHOX enhancer regions in a large cohort of short stature patients to study the importance of regulatory regions in developmentally relevant genes like SHOX.
The authors tested for the presence of copy number variations in the pseudoautosomal region of the sex chromosomes in 735 individuals with idiopathic short stature and compared the results to 58 cases with Leri–Weill syndrome and 100 normal height controls, using fluorescence in situ hybridisation (FISH), single nucleotide polymorphism (SNP), microsatellites, and multiplex ligand dependent probe amplification (MLPA) analysis.
A total of 31/735 (4.2%) microdeletions were identified in the pseudoautosomal region in patients with idiopathic short stature; eight of these microdeletions (8/31; 26%) involved only enhancer sequences residing a considerable distance away from the gene. In 58 Leri–Weill syndrome patients, a total of 29 microdeletions were identified; almost half of these (13/29; 45%) involve enhancer sequences and leave the SHOX gene intact. These deletions were absent in 100 control persons.
The authors conclude that enhancer deletions in the SHOX gene region are a relatively frequent cause of growth failure in patients with idiopathic short stature and Leri–Weill syndrome. The data highlights the growing recognition that regulatory sequences are of crucial importance in the genome when diagnosing and understanding the aetiology of disease.