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1.  The role of GHR and IGF1 genes in the genetic determination of African pygmies' short stature 
African pygmies are at the lower extreme of human variation in adult stature and many evolutionary hypotheses have been proposed to explain this phenotype. We showed in a recent study that the difference in average stature of about 10 cm observed between contemporary pygmies and neighboring non-pygmies has a genetic component. Nevertheless, the genetic basis of African pygmies' short stature remains unknown. Using a candidate-gene approach, we show that intronic polymorphisms in GH receptor (GHR) and insulin-like growth factor 1 (IGF1) genes present outlying values of the genetic distance between Baka pygmies and their non-pygmy Nzimé neighbors. We further show that GHR and IGF1 genes have experienced divergent natural selection pressures between pygmies and non-pygmies throughout evolution. In addition, these SNPs are associated with stature in a sample composed of 60 pygmies and 30 non-pygmies and this association remains significant when correcting for population structure for the GHR locus. We conclude that the GHR and IGF1 genes may have a role in African pygmies' short stature. The use of phenotypically contrasted populations is a promising strategy to identify new variants associated with complex traits in humans.
PMCID: PMC3658195  PMID: 23047741
pygmies; height; human evolution
2.  Involvement of the Same TNFR1 Residue in Mendelian and Multifactorial Inflammatory Disorders 
PLoS ONE  2013;8(7):e69757.
TNFRSF1A is involved in an autosomal dominant autoinflammatory disorder called TNFR-associated periodic syndrome (TRAPS). Most TNFRSF1A mutations are missense changes and, apart from those affecting conserved cysteines, their deleterious effect remains often questionable. This is especially true for the frequent R92Q mutation, which might not be responsible for TRAPS per se but represents a susceptibility factor to multifactorial inflammatory disorders. This study investigates TRAPS pathophysiology in a family exceptional by its size (13 members) and compares the consequences of several mutations affecting arginine 92.
TNFRSF1A screening was performed by PCR-sequencing. Comparison of the 3-dimensional structure and electrostatic properties of wild-type and mutated TNFR1 proteins was performed by in silico homology modeling. TNFR1 expression was assessed by FACS analysis, western blotting and ELISA in lysates and supernatants of HEK293T cells transiently expressing wild-type and mutated TNFR1.
A TNFRSF1A heterozygous missense mutation, R92W (c.361C>T), was shown to perfectly segregate with typical TRAPS manifestations within the family investigated (p<5.10−4). It was associated with very high disease penetrance (0.9). Prediction of its impact on the protein structure revealed local conformational changes and alterations of the receptor electrostatic properties. R92W also impairs the TNFR1 expression at the cell surface and the levels of soluble receptor. Similar results were obtained with R92P, another mutation previously identified in a very small familial form with incomplete penetrance and variable expressivity. In contrast, TNFR1-R92Q behaves like the wild-type receptor.
These data demonstrate the pathogenicity of a mutation affecting arginine 92, a residue whose involvement in inflammatory disorders is deeply debated. Combined with previous reports on arginine 92 mutations, this study discloses an unusual situation in which different amino acid substitutions at the same position in the protein are associated with a clinical spectrum bridging Mendelian to multifactorial conditions.
PMCID: PMC3722142  PMID: 23894535
3.  The Risk of Familial Mediterranean Fever in MEFV Heterozygotes: A Statistical Approach 
PLoS ONE  2013;8(7):e68431.
Familial Mediterranean fever (FMF) is an autosomal recessive autoinflammatory disorder due to MEFV mutations and one of the most frequent Mediterranean genetic diseases. The observation of many heterozygous patients in whom a second mutated allele was excluded led to the proposal that heterozygosity could be causal. However, heterozygosity might be coincidental in many patients due to the very high rate of mutations in Mediterranean populations.
To better delineate the pathogenicity of heterozygosity in order to improve genetic counselling and disease management.
Complementary statistical approaches were used: estimation of FMF prevalence at population levels, genotype comparison in siblings from 63 familial forms, and genotype study in 557 patients from four Mediterranean populations.
At the population level, we did not observe any contribution of heterozygosity to disease prevalence. In affected siblings of patients carrying two MEFV mutations, 92% carry two mutated alleles, whereas 4% are heterozygous with typical FMF diagnosis. We demonstrated statistically that patients are more likely to be heterozygous than healthy individuals, as shown by the higher ratio heterozygous carriers/non carriers in patients (p<10−7–p<0.003). The risk for heterozygotes to develop FMF was estimated between 2.1×10−3 and 5.8×10−3 and the relative risk, as compared to non carriers, between 6.3 and 8.1.
This is the first statistical demonstration that heterozygosity is not responsible for classical Mendelian FMF per se, but constitutes a susceptibility factor for clinically-similar multifactorial forms of the disease. We also provide a first estimate of the risk for heterozygotes to develop FMF.
PMCID: PMC3700951  PMID: 23844200
4.  CCDC39 is required for assembly of inner dynein arms and the dynein regulatory complex and for normal ciliary motility in humans and dogs 
Nature genetics  2010;43(1):72-78.
Primary ciliary dyskinesia (PCD) is an inherited disorder characterized by recurrent infections of the upper and lower respiratory tract, reduced fertility in males and situs inversus in about 50% of affected individuals (Kartagener syndrome). It is caused by motility defects in the respiratory cilia that are responsible for airway clearance, the flagella that propel sperm cells and the nodal monocilia that determine left-right asymmetry1. Recessive mutations that cause PCD have been identified in genes encoding components of the outer dynein arms, radial spokes and cytoplasmic pre-assembly factors of axonemal dyneins, but these mutations account for only about 50% of cases of PCD. We exploited the unique properties of dog populations to positionally clone a new PCD gene, CCDC39. We found that loss-of-function mutations in the human ortholog underlie a substantial fraction of PCD cases with axonemal disorganization and abnormal ciliary beating. Functional analyses indicated that CCDC39 localizes to ciliary axonemes and is essential for assembly of inner dynein arms and the dynein regulatory complex.
PMCID: PMC3509786  PMID: 21131972
6.  Involvement of the Modifier Gene of a Human Mendelian Disorder in a Negative Selection Process 
PLoS ONE  2009;4(10):e7676.
Identification of modifier genes and characterization of their effects represent major challenges in human genetics. SAA1 is one of the few modifiers identified in humans: this gene influences the risk of renal amyloidosis (RA) in patients with familial Mediterranean fever (FMF), a Mendelian autoinflammatory disorder associated with mutations in MEFV. Indeed, the SAA1 α homozygous genotype and the p.Met694Val homozygous genotype at the MEFV locus are two main risk factors for RA.
Methodology/Principal Findings
Here, we investigated Armenian FMF patients and controls from two neighboring countries: Armenia, where RA is frequent (24%), and Karabakh, where RA is rare (2.5%). Sequencing of MEFV revealed similar frequencies of p.Met694Val homozygotes in the two groups of patients. However, a major deficit of SAA1 α homozygotes was found among Karabakhian patients (4%) as compared to Armenian patients (24%) (p = 5.10−5). Most importantly, we observed deviations from Hardy-Weinberg equilibrium (HWE) in the two groups of patients, and unexpectedly, in opposite directions, whereas, in the two control populations, genotype distributions at this locus were similar and complied with (HWE).
The excess of SAA1α homozygotes among Armenian patients could be explained by the recruitment of patients with severe phenotypes. In contrast, a population-based study revealed that the deficit of α/α among Karabakhian patients would result from a negative selection against carriers of this genotype. This study, which provides new insights into the role of SAA1 in the pathophysiology of FMF, represents the first example of deviations from HWE and selection involving the modifier gene of a Mendelian disorder.
PMCID: PMC2765618  PMID: 19888326
7.  Oriented Scanning Is the Leading Mechanism Underlying 5′ Splice Site Selection in Mammals 
PLoS Genetics  2006;2(9):e138.
Splice site selection is a key element of pre-mRNA splicing. Although it is known to involve specific recognition of short consensus sequences by the splicing machinery, the mechanisms by which 5′ splice sites are accurately identified remain controversial and incompletely resolved. The human F7 gene contains in its seventh intron (IVS7) a 37-bp VNTR minisatellite whose first element spans the exon7–IVS7 boundary. As a consequence, the IVS7 authentic donor splice site is followed by several cryptic splice sites identical in sequence, referred to as 5′ pseudo-sites, which normally remain silent. This region, therefore, provides a remarkable model to decipher the mechanism underlying 5′ splice site selection in mammals. We previously suggested a model for splice site selection that, in the presence of consecutive splice consensus sequences, would stimulate exclusively the selection of the most upstream 5′ splice site, rather than repressing the 3′ following pseudo-sites. In the present study, we provide experimental support to this hypothesis by using a mutational approach involving a panel of 50 mutant and wild-type F7 constructs expressed in various cell types. We demonstrate that the F7 IVS7 5′ pseudo-sites are functional, but do not compete with the authentic donor splice site. Moreover, we show that the selection of the 5′ splice site follows a scanning-type mechanism, precluding competition with other functional 5′ pseudo-sites available on immediate sequence context downstream of the activated one. In addition, 5′ pseudo-sites with an increased complementarity to U1snRNA up to 91% do not compete with the identified scanning mechanism. Altogether, these findings, which unveil a cell type–independent 5′−3′-oriented scanning process for accurate recognition of the authentic 5′ splice site, reconciliate apparently contradictory observations by establishing a hierarchy of competitiveness among the determinants involved in 5′ splice site selection.
Typically, mammalian genes contain coding sequences (exons) separated by non-coding sequences (introns). Introns are removed during pre-mRNA splicing. The accurate recognition of introns during splicing is essential, as any abnormality in that process will generate abnormal mRNAs that can cause diseases. Understanding the mechanisms of accurate splice site selection is of prime interest to life scientists. Exon–intron borders (splice sites) are defined by short sequences that are poorly conserved. The strength of any splice sequence can be assessed by its degree of homology with a splice site consensus sequence. Within exons and introns, several sequences can match with this consensus as well as or better than the splice sites. Using a system in which a splice site sequence is repeated several times in the intron, the authors showed that linear 5′−3′ search is a leading mechanism underlying splice site selection. This scanning mechanism is cell type–independent, and only the most upstream splice site of all the series is selected, even if splice sites with a better match to the consensus are in the vicinity. These findings reconciliate contradictory observations and establish a hierarchy among the determinants involved in splice site selection.
PMCID: PMC1557585  PMID: 16948532

Results 1-7 (7)