Bardet-Biedl syndrome (BBS) is a genetically heterogeneous ciliopathy. Although nine BBS genes have been cloned, they explain only 40-50% of the total mutational load. Here we report a major new BBS locus, BBS10, that encodes a previously unknown, rapidly evolving vertebrate-specific chaperonin-like protein. We found BBS10 to be mutated in about 20% of an unselected cohort of families of various ethnic origins, including some families with mutations in other BBS genes, consistent with oligogenic inheritance. In zebrafish, mild suppression of bbs10 exacerbated the phenotypes of other bbs morphants.

Progressive pseudorheumatoid dysplasia (PPD) is a rare autosomal recessive syndrome characterized by the presence of spondyloepiphyseal dysplasia associated with pain, stiffness, and swelling of multiple joints, osteoporosis, and the absence of destructive bone changes. The disorder is caused by mutations of the WISP3 gene located on chromosome 6q22. We hereby report the molecular study of the WISP3 gene in nine unrelated consanguineous families originating from the Middle-East: three from Lebanon, five from Syria, and one from Palestinian Bedouin descent, all affected with PPD. Five different sequence variations were identified in the WISP3 gene, two of them being new mutations: the c.589G --> C transversion at codon 197, responsible for a splicing defect (A197fsX201); and the c.536_537delGT deletion (C179fsX), both in exon 3. In all other families, the affected patients were homozygous for a previously described nonsense mutation, namely c.156C --> A (C52X). Interestingly, in the latter families, the C52X mutation was always found associated with a novel c.248G --> A (G83E) variation, suggesting the existence of a founder effect.

ABSTRACT:Autosomal dominant hypercholesterolemia (ADH), a major risk for coronary heart disease, is associated with mutations in the genes encoding the low-density lipoproteins receptor (LDLR), its ligand apolipoprotein B (APOB) or PCSK9 (Proprotein Convertase Subtilin Kexin 9). Familial hypercholesterolemia (FH) caused by mutation in the LDLR gene is the most frequent form of ADH. The incidence of FH is particularly high in the Lebanese population presumably as a result of a founder effect. In this study we characterize the spectrum of the mutations causing FH in Lebanon: we confirm the very high frequency of the LDLR p.Cys681X mutation that accounts for 81.5 % of the FH Lebanese probands recruited and identify other less frequent mutations in the LDLR. Finally, we show that the p.Leu21dup, an in frame insertion of one leucine to the stretch of 9 leucines in exon 1 of PCSK9, known to be associated with lower LDL-cholesterol levels in general populations, is also associated with a reduction of LDL-cholesterol levels in FH patients sharing the p.C681X mutation in the LDLR. Thus, by studying for the first time the impact of PCSK9 polymorphism on LDL-cholesterol levels of FH patients carrying a same LDLR mutation, we show that PCSK9 might constitute a modifier gene in familial hypercholesterolemia.

BackgroundThe past few decades have witnessed a tremendous development in the field of genetics. The implementation of next generation sequencing (NGS) technologies revolutionized the field of molecular biology and made the genetic information accessible at a large scale. However, connecting a rare genetic variation to a complex phenotype remains challenging. Indeed, identifying the cause of a genetic disease requires a multidisciplinary approach, starting with the establishment of a clear phenotype with a detailed family history and ending, in some cases, with functional assays that are crucial for the validation of the pathogenicity of a mutation.MethodsTwo hundred Lebanese patients, presenting a wide spectrum of genetic disorders (neurodevelopmental, neuromuscular or metabolic disorders, etc.), sporadic or inherited, dominant or recessive, were referred, over the last three and a half years, to the Medical Genetics Unit (UGM) of Saint Joseph University (USJ). In order to identify the genetic basis of these diseases, Whole Exome Sequencing (WES), followed by a targeted analysis, was performed for each case. In order to improve the genetic diagnostic yield, WES data, generated during the first 2 years of this study, were reanalyzed for all patients who were left undiagnosed at the genetic level. Reanalysis was based on updated bioinformatics tools and novel gene discoveries.ResultsOur initial analysis allowed us to identify the specific genetic mutation causing the disease in 49.5% of the cases, in line with other international studies. Repeated WES analysis enabled us to increase the diagnostics yield to 56%.ConclusionThe present article reports the detailed results of both analysis and pinpoints the contribution of WES data reanalysis to an efficient genetic diagnosis. Lessons learned from WES reanalysis and interpretation are also shared.

The extensive genetic heterogeneity of Bardet-Biedl syndrome (BBS) is documented by the identification, by classical linkage analysis complemented recently by comparative genomic approaches, of nine genes (BBS1-9) that account cumulatively for about 50% of patients. The BBS genes appear implicated in cilia and basal body assembly or function. In order to find new BBS genes, we performed SNP homozygosity mapping analysis in an extended consanguineous family living in a small Lebanese village. This uncovered an unexpectedly complex pattern of mutations, and led us to identify a novel BBS gene (BBS10). In one sibship of the pedigree, a BBS2 homozygous mutation was identified, while in three other sibships, a homozygous missense mutation was identified in a gene encoding a vertebrate-specific chaperonine-like protein (BBS10). The single patient in the last sibship was a compound heterozygote for the above BBS10 mutation and another one in the same gene. Although triallelism (three deleterious alleles in the same patient) has been described in some BBS families, we have to date no evidence that this is the case in the present family. The analysis of this family challenged linkage analysis based on the expectation of a single locus and mutation. The very high informativeness of SNP arrays was instrumental in elucidating this case, which illustrates possible pitfalls of homozygosity mapping in extended families, and that can be explained by the rather high prevalence of heterozygous carriers of BBS mutations (estimated at one in 50 in Europeans).