Children with autism have an elevated frequency of large, rare copy number variants (CNVs). However, the global load of deletions or duplications, per se, and their size, location and relationship to clinical manifestations of autism have not been documented. We examined CNV data from 516 individuals with autism or typical development from the population-based Childhood Autism Risks from Genetics and Environment (CHARGE) study. We interrogated 120 regions flanked by segmental duplications (genomic hotspots) for events >50 kbp and the entire genomic backbone for variants >300 kbp using a custom targeted DNA microarray. This analysis was complemented by a separate study of five highly dynamic hotspots associated with autism or developmental delay syndromes, using a finely tiled array platform (>1 kbp) in 142 children matched for gender and ethnicity. In both studies, a significant increase in the number of base pairs of duplication, but not deletion, was associated with autism. Significantly elevated levels of CNV load remained after the removal of rare and likely pathogenic events. Further, the entire CNV load detected with the finely tiled array was contributed by common variants. The impact of this variation was assessed by examining the correlation of clinical outcomes with CNV load. The level of personal and social skills, measured by Vineland Adaptive Behavior Scales, negatively correlated (Spearman's r = −0.13, P = 0.034) with the duplication CNV load for the affected children; the strongest association was found for communication (P = 0.048) and socialization (P = 0.022) scores. We propose that CNV load, predominantly increased genomic base pairs of duplication, predisposes to autism.
The lamprey (Petromyzon marinus) undergoes developmentally programmed genome rearrangements (PGRs) that mediate deletion of ~20% of germline DNA from somatic cells during early embryogenesis. This genomic differentiation of germline and soma is intriguing, because the germline plays a unique biological role wherein it must possess the ability to undergo meiotic recombination and the capacity to differentiate into every cell type. These evolutionarily indispensible functions set the germline at odds with somatic tissues, as factors that promote recombination and pluripotency can potentially disrupt genome integrity or specification of cell fate when misexpressed in somatic cell lineages (e.g. in oncogenesis). Here, we describe the development of new genomic and transcriptomic resources for lamprey and use these to identify hundreds of genes that are targeted for programmed deletion from somatic cell lineages. Transcriptome sequencing and targeted validation studies further confirm that somatically deleted genes function both in adult (meiotic) germline and in the development of primordial germ cells during embryogenesis. Inferred functional information from deleted regions indicates that developmentally programmed rearrangement serves as a (perhaps ancient) biological strategy to ensure segregation of pluripotency functions to the germline, effectively eliminating the potential for somatic misexpression.
To evaluate the success of masking study participants to treatment allocation using sham intravitreal injections.
Eyes were randomized to prompt laser plus sham injections, prompt laser plus intravitreal ranibizumab injections, deferred laser plus intravitreal ranibizumab injections, or prompt laser plus intravitreal triamcinolone injections up to every 16 weeks with sham injections intermittently. All eyes could receive treatment or sham as often as every 4 weeks. Participants with 2 study eyes had one eye randomized to sham+laser and one eye randomized to a real injection group. Sham injections were performed by pressing the syringe hub against the conjunctiva to mimic a real injection. Laser treatment was not masked. At the 1 year visit, participants were asked if they believed the injections received during the study were real, sham, or sometimes real and sometimes sham.
Among 423 participants with one study eye, the correct assignment was stated by 10% of the sham+prompt laser group, 88% of the ranibizumab+prompt laser group, 90% of the unmasked ranibizumab+deferred laser group, and 44% of the triamcinolone+laser group. Among the 112 participants with 2 study eyes, the correct assignment was stated for 24% of the sham+prompt laser eyes.
Successful masking of an intravitreal injection can be accomplished when a sham injection procedure carefully mimics a true injection procedure. Masking appears less successful when one eye is receiving a real injection and the other eye is receiving a sham injection or an individual eye sometimes receives a real and sometimes a sham injection.
It is well established that autism spectrum disorders (ASD) have a strong genetic component. However, for at least 70% of cases, the underlying genetic cause is unknown1. Under the hypothesis that de novo mutations underlie a substantial fraction of the risk for developing ASD in families with no previous history of ASD or related phenotypes—so-called sporadic or simplex families2,3, we sequenced all coding regions of the genome, i.e. the exome, for parent-child trios exhibiting sporadic ASD, including 189 new trios and 20 previously reported4. Additionally, we also sequenced the exomes of 50 unaffected siblings corresponding to these new (n = 31) and previously reported trios (n = 19)4, for a total of 677 individual exomes from 209 families. Here we show de novo point mutations are overwhelmingly paternal in origin (4:1 bias) and positively correlated with paternal age, consistent with the modest increased risk for children of older fathers to develop ASD5. Moreover, 39% (49/126) of the most severe or disruptive de novo mutations map to a highly interconnected beta-catenin/chromatin remodeling protein network ranked significantly for autism candidate genes. In proband exomes, recurrent protein-altering mutations were observed in two genes, CHD8 and NTNG1. Mutation screening of six candidate genes in 1,703 ASD probands identified additional de novo, protein-altering mutations in GRIN2B, LAMC3, and SCN1A. Combined with copy number variant (CNV) data, these results suggest extreme locus heterogeneity but also provide a target for future discovery, diagnostics, and therapeutics.
To understand the genetic heterogeneity underlying developmental delay, we compare copy-number variants (CNVs) in 15,767 children with intellectual disability and various congenital defects to 8,329 adult controls. We estimate that ~14.2% of disease in these individuals is due to large CNVs > 400 kbp. We find greater CNV enrichment in patients with craniofacial anomalies and cardiovascular defects than epilepsy or autism. We identify 59 pathogenic CNVs including 14 novel or previously weakly supported candidates. We refine the critical interval for several genomic disorders such as the 17q21.31 microdeletion syndrome and identify 940 candidate dosage-sensitive genes. We also develop methods to opportunistically discover small, disruptive CNVs within the large and growing diagnostic array datasets. This evolving CNV morbidity map combined with exome/genome sequencing will be critical for deciphering the genetic basis of developmental delay, intellectual disability, and autism spectrum disorders.
Evidence for the etiology of autism spectrum disorders (ASD) has consistently pointed to a strong genetic component complicated by substantial locus heterogeneity1,2. We sequenced the exomes of 20 sporadic cases of ASD and their parents, reasoning that these families would be enriched for de novo mutations of major effect. We identified 21 de novo mutations, of which 11 were protein-altering. Protein-altering mutations were significantly enriched for changes at highly conserved residues. We identified potentially causative de novo events in 4/20 probands, particularly among more severely affected individuals, in FOXP1, GRIN2B, SCN1A, and LAMC3. In the FOXP1 mutation carrier, we also observed a rare inherited CNTNAP2 mutation and provide functional support for a multihit model for disease risk3. Our results demonstrate that trio-based exome sequencing is a powerful approach for identifying novel candidate genes for ASD and suggest that de novo mutations may contribute substantially to the genetic risk for ASD.
While numerous studies have implicated copy number variants (CNVs) in a range of neurological phenotypes, the impact relative to disease severity has been difficult to ascertain due to small sample sizes, lack of phenotypic details, and heterogeneity in platforms used for discovery. Using a customized microarray enriched for genomic hotspots, we assayed for large CNVs among 1,227 individuals with various neurological deficits including dyslexia (376), sporadic autism (350), and intellectual disability (ID) (501), as well as 337 controls. We show that the frequency of large CNVs (>1 Mbp) is significantly greater for ID–associated phenotypes compared to autism (p = 9.58×10−11, odds ratio = 4.59), dyslexia (p = 3.81×10−18, odds ratio = 14.45), or controls (p = 2.75×10−17, odds ratio = 13.71). There is a striking difference in the frequency of rare CNVs (>50 kbp) in autism (10%, p = 2.4×10−6, odds ratio = 6) or ID (16%, p = 3.55×10−12, odds ratio = 10) compared to dyslexia (2%) with essentially no difference in large CNV burden among dyslexia patients compared to controls. Rare CNVs were more likely to arise de novo (64%) in ID when compared to autism (40%) or dyslexia (0%). We observed a significantly increased large CNV burden in individuals with ID and multiple congenital anomalies (MCA) compared to ID alone (p = 0.001, odds ratio = 2.54). Our data suggest that large CNV burden positively correlates with the severity of childhood disability: ID with MCA being most severely affected and dyslexics being indistinguishable from controls. When autism without ID was considered separately, the increase in CNV burden was modest compared to controls (p = 0.07, odds ratio = 2.33).
Deletions and duplications, termed copy number variants (CNVs), have been implicated in a variety of neurodevelopmental disorders including intellectual disability (ID), autism, and schizophrenia. Our understanding of the relevance of large, rare CNVs in a range of neurodevelopmental phenotypes, varying in severity and prevalence, has been difficult because these studies were restricted to the analysis of one disorder at a time using different CNV detection platforms, insufficient sample sizes, and a lack of detailed clinical information. We tested 1,227 individuals with different neurological diseases including dyslexia, autism, and ID using the same CNV detection platform. We observed striking differences in CNV burden and inheritance characteristics among these cohorts and show that ID is the primary correlate of large CNV burden. This correlation is well illustrated by a comparison of autism patients with and without ID—where the latter show only modest increases in large CNV burden compared to controls. We also find significant depletion in the frequency of large CNVs in dyslexia compared to the other cohorts. Further studies on larger sets of individuals using high-resolution arrays and next-generation sequencing are warranted for a detailed understanding of the relative contribution of genetic variants to neurodevelopmental disorders.
Structural variation contributes to the rich genetic and phenotypic diversity of the modern domestic dog, Canis lupus familiaris, although compared to other organisms, catalogs of canine copy number variants (CNVs) are poorly defined. To this end, we developed a customized high-density tiling array across the canine genome and used it to discover CNVs in nine genetically diverse dogs and a gray wolf.
In total, we identified 403 CNVs that overlap 401 genes, which are enriched for defense/immunity, oxidoreductase, protease, receptor, signaling molecule and transporter genes. Furthermore, we performed detailed comparisons between CNVs located within versus outside of segmental duplications (SDs) and find that CNVs in SDs are enriched for gene content and complexity. Finally, we compiled all known dog CNV regions and genotyped them with a custom aCGH chip in 61 dogs from 12 diverse breeds. These data allowed us to perform the first population genetics analysis of canine structural variation and identify CNVs that potentially contribute to breed specific traits.
Our comprehensive analysis of canine CNVs will be an important resource in genetically dissecting canine phenotypic and behavioral variation.
In communities with high rates of consanguinity and consequently high prevalence of recessive phenotypes, homozygosity mapping with SNP arrays is an effective approach for gene discovery. In 20 Palestinian kindreds with prelingual nonsyndromic hearing loss, we generated homozygosity profiles reflecting linkage to the phenotype. Family sizes ranged from small nuclear families with two affected children, one unaffected sibling, and parents to multigenerational kindreds with 12 affected relatives. By including unaffected parents and siblings and screening 250 K SNP arrays, even small nuclear families yielded informative profiles. In 14 families, we identified the allele responsible for hearing loss by screening a single candidate gene in the longest homozygous region. Novel alleles included missense, nonsense, and splice site mutations of CDH23, MYO7A, MYO15A, OTOF, PJVK, Pendrin/SLC26A4, TECTA, TMHS, and TMPRSS3, and a large genomic deletion of Otoancorin (OTOA). All point mutations were rare in the Palestinian population (zero carriers in 288 unrelated controls); the carrier frequency of the OTOA genomic deletion was 1%. In six families, we identified five genomic regions likely to harbor novel genes for human hearing loss on chromosomes 1p13.3 (DFNB82), 9p23–p21.2/p13.3–q21.13 (DFNB83), 12q14.3–q21.2 (DFNB84; two families), 14q23.1–q31.1, and 17p12–q11.2 (DFNB85).
hearing; deafness; DFNB; homozygosity mapping; mutation; protein modeling
Mutations in two branch-point sequences (BPS) in intron 3 of the XPC DNA repair gene affect pre-mRNA splicing in association with xeroderma pigmentosum (XP) with many skin cancers (XP101TMA) or no skin cancer (XP72TMA), respectively. To investigate the mechanism of these abnormalities we now report that transfection of minigenes with these mutations revealed abnormal XPC pre-mRNA splicing that mimicked pre-mRNA splicing in the patients’ cells. DNA oligonucleotide-directed RNase H digestion demonstrated that mutations in these BPS disrupt U2 snRNP – BPS interaction. XP101TMA cells had no detectable XPC protein but XP72TMA had 29% of normal levels. A small amount of XPC protein was detected at sites of localized UV-damaged DNA in XP72TMA cells which then recruited other nucleotide excision repair (NER) proteins. In contrast, XP101TMA cells had no detectable recruitment of XPC or other NER proteins. Post-UV survival and photoproduct assays revealed greater reduction in DNA repair in XP101TMA cells than in XP72TMA. Thus mutations in XPC BPS resulted in disruption of U2 snRNP-BPS interaction leading to abnormal pre-mRNA splicing and reduced XPC protein. At the cellular level these changes were associated with features of reduced DNA repair including diminished NER protein recruitment, reduced post-UV survival and impaired photoproduct removal.
XPC; DNA repair; pre-mRNA splicing; xeroderma pigmentosum; skin cancer; U2 snRNP
We identified 15q13.3 microdeletions encompassing the CHRNA7 gene in 12 of 1,223 individuals with idiopathic generalized epilepsy (IGE), which were not detected in 3,699 controls (joint P = 5.32 × 10−8). Most deletion carriers showed common IGE syndromes without other features previously associated with 15q13.3 microdeletions, such as intellectual disability, autism or schizophrenia. Our results indicate that 15q13.3 microdeletions constitute the most prevalent risk factor for common epilepsies identified to date.
Idiopathic generalized epilepsies account for 30% of all epilepsies. Despite a predominant genetic aetiology, the genetic factors predisposing to idiopathic generalized epilepsies remain elusive. Studies of structural genomic variations have revealed a significant excess of recurrent microdeletions at 1q21.1, 15q11.2, 15q13.3, 16p11.2, 16p13.11 and 22q11.2 in various neuropsychiatric disorders including autism, intellectual disability and schizophrenia. Microdeletions at 15q13.3 have recently been shown to constitute a strong genetic risk factor for common idiopathic generalized epilepsy syndromes, implicating that other recurrent microdeletions may also be involved in epileptogenesis. This study aimed to investigate the impact of five microdeletions at the genomic hotspot regions 1q21.1, 15q11.2, 16p11.2, 16p13.11 and 22q11.2 on the genetic risk to common idiopathic generalized epilepsy syndromes. The candidate microdeletions were assessed by high-density single nucleotide polymorphism arrays in 1234 patients with idiopathic generalized epilepsy from North-western Europe and 3022 controls from the German population. Microdeletions were validated by quantitative polymerase chain reaction and their breakpoints refined by array comparative genomic hybridization. In total, 22 patients with idiopathic generalized epilepsy (1.8%) carried one of the five novel microdeletions compared with nine controls (0.3%) (odds ratio = 6.1; 95% confidence interval 2.8–13.2; χ2 = 26.7; 1 degree of freedom; P = 2.4 × 10−7). Microdeletions were observed at 1q21.1 [Idiopathic generalized epilepsy (IGE)/control: 1/1], 15q11.2 (IGE/control: 12/6), 16p11.2 IGE/control: 1/0, 16p13.11 (IGE/control: 6/2) and 22q11.2 (IGE/control: 2/0). Significant associations with IGEs were found for the microdeletions at 15q11.2 (odds ratio = 4.9; 95% confidence interval 1.8–13.2; P = 4.2 × 10−4) and 16p13.11 (odds ratio = 7.4; 95% confidence interval 1.3–74.7; P = 0.009). Including nine patients with idiopathic generalized epilepsy in this cohort with known 15q13.3 microdeletions (IGE/control: 9/0), parental transmission could be examined in 14 families. While 10 microdeletions were inherited (seven maternal and three paternal transmissions), four microdeletions occurred de novo at 15q13.3 (n = 1), 16p13.11 (n = 2) and 22q11.2 (n = 1). Eight of the transmitting parents were clinically unaffected, suggesting that the microdeletion itself is not sufficient to cause the epilepsy phenotype. Although the microdeletions investigated are individually rare (<1%) in patients with idiopathic generalized epilepsy, they collectively seem to account for a significant fraction of the genetic variance in common idiopathic generalized epilepsy syndromes. The present results indicate an involvement of microdeletions at 15q11.2 and 16p13.11 in epileptogenesis and strengthen the evidence that recurrent microdeletions at 15q11.2, 15q13.3 and 16p13.11 confer a pleiotropic susceptibility effect to a broad range of neuropsychiatric disorders.
idiopathic generalized epilepsy; microdeletions; association; genetics
We report the identification of a recurrent 520-kbp 16p12.1 microdeletion significantly associated with childhood developmental delay. The microdeletion was detected in 20/11,873 cases vs. 2/8,540 controls (p=0.0009, OR=7.2) and replicated in a second series of 22/9,254 cases vs. 6/6,299 controls (p=0.028, OR=2.5). Most deletions were inherited with carrier parents likely to manifest neuropsychiatric phenotypes (p=0.037, OR=6). Probands were more likely to carry an additional large CNV when compared to matched controls (10/42 cases, p=5.7×10-5, OR=6.65). Clinical features of cases with two mutations were distinct from and/or more severe than clinical features of patients carrying only the co-occurring mutation. Our data suggest a two-hit model in which the 16p12.1 microdeletion both predisposes to neuropsychiatric phenotypes as a single event and exacerbates neurodevelopmental phenotypes in association with other large deletions or duplications. Analysis of other microdeletions with variable expressivity suggests that this two-hit model may be more generally applicable to neuropsychiatric disease.
Despite their importance in gene innovation and phenotypic variation, duplicated regions have remained largely intractable due to difficulties in accurately resolving their structure, copy number and sequence content. We present an algorithm (mrFAST) to comprehensively map next-generation sequence reads allowing for the prediction of absolute copy-number variation of duplicated segments and genes. We examine three human genomes and experimentally validate genome-wide copy-number differences. We estimate that 73–87 genes will be on average copy-number variable between two human genomes and find that these genic differences overwhelmingly correspond to segmental duplications (OR=135; p<2.2e-16). Our method can distinguish between different copies of highly identical genes, providing a more accurate census of gene content and insight into functional constraint without the limitations of array-based technology.
Epilepsy is one of the most common neurological disorders in humans with a prevalence of 1% and a lifetime incidence of 3%. Several genes have been identified in rare autosomal dominant and severe sporadic forms of epilepsy, but the genetic cause is unknown in the vast majority of cases. Copy number variants (CNVs) are known to play an important role in the genetic etiology of many neurodevelopmental disorders, including intellectual disability (ID), autism, and schizophrenia. Genome-wide studies of copy number variation in epilepsy have not been performed. We have applied whole-genome oligonucleotide array comparative genomic hybridization to a cohort of 517 individuals with various idiopathic, non-lesional epilepsies. We detected one or more rare genic CNVs in 8.9% of affected individuals that are not present in 2,493 controls; five individuals had two rare CNVs. We identified CNVs in genes previously implicated in other neurodevelopmental disorders, including two deletions in AUTS2 and one deletion in CNTNAP2. Therefore, our findings indicate that rare CNVs are likely to contribute to a broad range of generalized and focal epilepsies. In addition, we find that 2.9% of patients carry deletions at 15q11.2, 15q13.3, or 16p13.11, genomic hotspots previously associated with ID, autism, or schizophrenia. In summary, our findings suggest common etiological factors for seemingly diverse diseases such as ID, autism, schizophrenia, and epilepsy.
Epilepsy, a common neurological disorder characterized by recurrent seizures, affects up to 3% of the population. In some cases, the epilepsy has a clear cause such as an abnormality in the brain or a head injury. However, in many cases there is no obvious cause. Numerous studies have shown that genetic factors are important in these types of epilepsy, but although several epilepsy genes are known, we can still only identify the genetic cause in a very small fraction of cases. In order to identify new genes that contribute to the genetic causes of epilepsy, we searched the human genome for deletions (missing copies) and duplications (extra copies) of genes in ∼500 patients with epilepsy that are not found in control individuals. Using this approach, we identified several large deletions that are important in at least 3% of epilepsy cases. Furthermore, we found new candidate genes, some of which are also thought to play a role in other related disorders such as autism and intellectual disability. These genes are candidates for further studies in patients with epilepsy.
Two unrelated xeroderma pigmentosum (XP) patients, with and without neurological abnormalities respectively, had identical defects in the XPC DNA nucleotide excision repair (NER) gene. Patient XP21BE, a 27 y/o woman, had developmental delay and early onset of sensorineural hearing loss. In contrast, patient XP329BE, a 13 y/o boy, had a normal neurological examination. Both patients had marked lentiginous hyperpigmentation and multiple skin cancers at an early age. Their cultured fibroblasts showed similar hypersensitivity to killing by UV and reduced repair of DNA photoproducts. Cells from both patients had a homozygous c.2T>G mutation in the XPC gene which changed the ATG initiation codon to arginine. Both had low levels of XPC message and no detectable XPC protein on Western blotting. There was no functional XPC activity in both as revealed by the failure of localization of XPC and other NER proteins at the sites of UV-induced DNA in a sensitive in vivo immunofluorescence assay. XPC cDNA containing the initiation codon mutation was functionally inactive in a post-UV host cell reactivation assay. Microsatellite markers flanking the XPC gene showed only a small region of identity (~30kBP), indicating that the patients were not closely related. Thus, the initiation codon mutation resulted in DNA repair deficiency in cells from both patients and greatly increased cancer susceptibility. The neurological abnormalities in patient XP21BE may be related to close consanguinity and simultaneous inheritance of other recessive genes or other gene modifying effects rather than the influence of XPC gene itself.
DNA Repair; molecular genetics; sensorineural hearing loss; skin cancer; xeroderma pigmentosum
Wilson and King were among the first to recognize that the extent of phenotypic change between humans and great apes was dissonant with the rate of molecular change. Proteins are virtually identical1,2; cytogenetically there are few rearrangements that distinguish ape-human chromosomes3; rates of single-basepair change4-7 and retroposon activity8-10 have slowed particularly within hominid lineages when compared to rodents or monkeys. Here, we perform a systematic analysis of duplication content of four primate genomes (macaque, orangutan, chimpanzee and human) in an effort to understand the pattern and rates of genomic duplication during hominid evolution. We find that the ancestral branch leading to human and African great apes shows the most significant increase in duplication activity both in terms of basepairs and in terms of events. This duplication acceleration within the ancestral species is significant when compared to lineage-specific rate estimates even after accounting for copy-number polymorphism and homoplasy. We discover striking examples of recurrent and independent gene-containing duplications within the gorilla and chimpanzee that are absent in the human lineage. Our results suggest that the evolutionary properties of copy-number mutation differ significantly from other forms of genetic mutation and, in contrast to the hominid slowdown of single basepair mutations, there has been a genomic burst of duplication activity at this period during human evolution.
The viral early-to-late switch of papillomavirus infection is tightly linked to keratinocyte differentiation and is mediated in part by alternative mRNA splicing. Here, we report that SRp20, a cellular splicing factor, controls the early-to-late switch via interactions with A/C-rich RNA elements. An A/C-rich SE4 element regulates the selection of a bovine papillomavirus type 1 (BPV-1) late-specific splice site, and binding of SRp20 to SE4 suppresses this selection. Expression of late BPV-1 L1 or human papillomavirus (HPV) L1, the major capsid protein, inversely correlates with SRp20 levels in the terminally differentiated keratinocytes. In HPV type 16, a similar SRp20-interacting element also controls the viral early-to-late switch. Keratinocytes in raft cultures, which support L1 expression, make considerably less SRp20 than keratinocytes in monolayer cultures, which do not support L1 expression. Conversely, abundant SRp20 in cancer cells or undifferentiated keratinocytes is important for the expression of the viral early E6 and E7 by promoting the expression of cellular transcription factor SP1 for transactivation of viral early promoters.
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.
Xeroderma pigmentosum-variant (XP-V) patients have sun sensitivity and increased skin cancer risk. Their cells have normal nucleotide excision repair, but have defects in the POLH gene encoding an error-prone polymerase, DNA polymeraseη (polη). To survey the molecular basis of XP-V worldwide, we measured polη protein in skin fibroblasts from putative XP-V patients (aged 8–66 years) from 10 families in North America, Turkey, Israel, Germany, and Korea. Polη was undetectable in cells from patients in eight families, whereas two showed faint bands. DNA sequencing identified 10 different POLH mutations. There were two splicing, one nonsense, five frameshift (3 deletion and 2 insertion), and two missense mutations. Nine of these mutations involved the catalytic domain. Although affected siblings had similar clinical features, the relation between the clinical features and the mutations was not clear. POLH mRNA levels were normal or reduced by 50% in three cell strains with undetectable levels of polη protein, indicating that nonsense-mediated message decay was limited. We found a wide spectrum of mutations in the POLH gene among XP-V patients in different countries, suggesting that many of these mutations arose independently.
We report a recurrent microdeletion syndrome causing mental retardation, epilepsy and variable facial and digital dysmorphisms. We describe nine patients, including six probands; two with de novo deletions, two who inherited the deletion from an affected parent, and two with unknown inheritance. The proximal breakpoint of the largest deletion is contiguous with breakpoint 3 (BP3) of the Prader-Willi and Angelman syndrome region extending 3.95 Mb distally to BP5. A smaller 1.5 Mb deletion has proximal breakpoint within the larger deletion (BP4) and shares the same distal BP5. This recurrent 1.5 Mb deletion contains six genes, including a candidate gene for epilepsy (CHRNA7) that is likely responsible for the observed seizure phenotype. The BP4-BP5 region undergoes frequent inversion, suggesting a possible link between this inversion polymorphism and recurrent deletion. The frequency of these microdeletions in mental retardation cases is ~0.3% (6/2082 tested), a prevalence comparable to that of the Williams, Angelman, and Prader-Willi syndromes.
genomic disorder; array CGH; epilepsy; segmental duplication; CHRNA7
Papillomaviruses are a group of small non-enveloped DNA tumor viruses whose infection usually causes benign epithelial lesions (warts). Certain types of HPVs, such as HPV-16, HPV-18, and HPV-31, have been recognized as causative agents of cervical cancer and anal cancer and their infections, which arise via sexual transmission, are associated with more than 95% of cervical cancer. Papillomaviruses infect keratinocytes in the basal layer of stratified squamous epithelia and replicate in the nucleus of infected keratinocytes in a differentiation-dependent manner. Viral gene expression in infected cells depends on cell differentiation and is tightly regulated at the transcriptional and post-transcriptional levels. A noteworthy feature of all papillomavirus transcripts is that they are transcribed as a bicistronic or polycistronic form containing two or more ORFs and are polyadenylated at either an early or late poly(A) site. In the past ten years, remarkable progress has been made in understanding how this complex viral gene expression is regulated at the level of transcription (such as via DNA methylation) and particularly post-transcription (including RNA splicing, polyadenylation, and translation). Current knowledge of papillomavirus mRNA structure and RNA processing has provided some clues on how to control viral oncogene expression. However, we still have little knowledge about which mRNAs are used to translate each viral protein. Continuing research on post-transcriptional regulation of papillomavirus infection will remain as a future focus to provide more insights into papillomavirus-host interactions, the virus life-cycle, and viral oncogenesis.
papillomaviruses; gene expression; RNA splicing; RNA polyadenylation; posttranscriptional regulation
XPC DNA repair gene mutations result in the cancer-prone disorder xeroderma pigmentosum. The XPC gene spans 33 kb and has 16 exons (82–882 bp) and 15 introns (0.08–5.4 kb). A 1.6 kb intron was found within exon 5. Sensitive real- time quantitative reverse transcription–polymerase chain reaction methods were developed to measure full-length XPC mRNA (the predominant form) and isoforms that skipped exons 4, 7 or 12. Exon 7 was skipped in ∼0.07% of XPC mRNAs, consistent with the high information content of the exon 7 splice acceptor and donor sites (12.3 and 10.4 bits). In contrast, exon 4 was skipped in ∼0.7% of the XPC mRNAs, consistent with the low information content of the exon 4 splice acceptor (–0.1 bits). A new common C/A single nucleotide polymorphism in the XPC intron 11 splice acceptor site (58% C in 97 normals) decreased its information content from 7.5 to 5.1 bits. Fibroblasts homozygous for A/A had significantly higher levels (∼2.6-fold) of the XPC mRNA isoform that skipped exon 12 than those homozygous for C/C. This abnormally spliced XPC mRNA isoform has diminished DNA repair function and may contribute to cancer susceptibility.
Bovine papillomavirus type 1 (BPV-1) late gene expression is regulated at both transcriptional and posttranscriptional levels. Maturation of the capsid protein (L1) pre-mRNA requires a switch in 3′ splice site utilization. This switch involves activation of the nucleotide (nt) 3605 3′ splice site, which is utilized only in fully differentiated keratinocytes during late stages of the virus life cycle. Our previous studies of the mechanisms that regulate BPV-1 alternative splicing identified three cis-acting elements between these two splice sites. Two purine-rich exonic splicing enhancers, SE1 and SE2, are essential for preferential utilization of the nt 3225 3′ splice site at early stages of the virus life cycle. Another cis-acting element, exonic splicing suppressor 1 (ESS1), represses use of the nt 3225 3′ splice site. In the present study, we investigated the late-stage-specific nt 3605 3′ splice site and showed that it has suboptimal features characterized by a nonconsensus branch point sequence and a weak polypyrimidine track with interspersed purines. In vitro and in vivo experiments showed that utilization of the nt 3605 3′ splice site was not affected by SE2, which is intronically located with respect to the nt 3605 3′ splice site. The intronic location and sequence composition of SE2 are similar to those of the adenovirus IIIa repressor element, which has been shown to inhibit use of a downstream 3′ splice site. Further studies demonstrated that the nt 3605 3′ splice site is controlled by a novel exonic bipartite element consisting of an AC-rich exonic splicing enhancer (SE4) and an exonic splicing suppressor (ESS2) with a UGGU motif. Functionally, this newly identified bipartite element resembles the bipartite element composed of SE1 and ESS1. SE4 also functions on a heterologous 3′ splice site. In contrast, ESS2 functions as an exonic splicing suppressor only in a 3′-splice-site-specific and enhancer-specific manner. Our data indicate that BPV-1 splicing regulation is very complex and is likely to be controlled by multiple splicing factors during keratinocyte differentiation.
Alternative splicing is a critical component of the early to late switch in papillomavirus gene expression. In bovine papillomavirus type 1 (BPV-1), a switch in 3′ splice site utilization from an early 3′ splice site at nucleotide (nt) 3225 to a late-specific 3′ splice site at nt 3605 is essential for expression of the major capsid (L1) mRNA. Three viral splicing elements have recently been identified between the two alternative 3′ splice sites and have been shown to play an important role in this regulation. A bipartite element lies approximately 30 nt downstream of the nt 3225 3′ splice site and consists of an exonic splicing enhancer (ESE), SE1, followed immediately by a pyrimidine-rich exonic splicing suppressor (ESS). A second ESE (SE2) is located approximately 125 nt downstream of the ESS. We have previously demonstrated that the ESS inhibits use of the suboptimal nt 3225 3′ splice site in vitro through binding of cellular splicing factors. However, these in vitro studies did not address the role of the ESS in the regulation of alternative splicing. In the present study, we have analyzed the role of the ESS in the alternative splicing of a BPV-1 late pre-mRNA in vivo. Mutation or deletion of just the ESS did not significantly change the normal splicing pattern where the nt 3225 3′ splice site is already used predominantly. However, a pre-mRNA containing mutations in SE2 is spliced predominantly using the nt 3605 3′ splice site. In this context, mutation of the ESS restored preferential use of the nt 3225 3′ splice site, indicating that the ESS also functions as a splicing suppressor in vivo. Moreover, optimization of the suboptimal nt 3225 3′ splice site counteracted the in vivo function of the ESS and led to preferential selection of the nt 3225 3′ splice site even in pre-mRNAs with SE2 mutations. In vitro splicing assays also showed that the ESS is unable to suppress splicing of a pre-mRNA with an optimized nt 3225 3′ splice site. These data confirm that the function of the ESS requires a suboptimal upstream 3′ splice site. A surprising finding of our study is the observation that SE1 can stimulate both the first and the second steps of splicing.