Nabiha Salem

A defect in harmonin, a PDZ domain-containing protein expressed in the inner ear sensory hair cells, underlies Usher syndrome type 1C

Usher syndrome type 1 (USH1) is an autosomal recessive sensory defect involving congenital profound sensorineural deafness, vestibular dysfunction and blindness (due to progressive retinitis pigmentosa). Six different USH1 loci have been reported. So far, only MYO7A (USH1B), encoding myosin VIIA (ref. 2), has been identified as a gene whose mutation causes the disease. Here, we report a gene underlying USH1C (MIM 276904), a USH1 subtype described in a population of Acadian descendants from Louisiana and in a Lebanese family. We identified this gene (USH1C), encoding a PDZ-domain–containing protein, harmonin, in a subtracted mouse cDNA library derived from inner ear sensory areas. In patients we found a splice-site mutation, a frameshift mutation and the expansion of an intronic variable number of tandem repeat (VNTR). We showed that, in the mouse inner ear, only the sensory hair cells express harmonin. The inner ear Ush1c transcripts predicted several harmonin isoforms, some containing an additional coiled-coil domain and a proline- and serine-rich region. As several of these transcripts were absent from the eye, we propose that USH1C also underlies the DFNB18 form of isolated deafness.

A mutation in OTOF, encoding otoferlin, a FER-1-like protein, causes DFNB9, a nonsyndromic form of deafness

Using a candidate gene approach, we identified a novel human gene, OTOF, underlying an autosomal recessive, nonsyndromic prelingual deafness, DFNB9. The same nonsense mutation was detected in four unrelated affected families of Lebanese origin. OTOF is the second member of a mammalian gene family related to Caenorhabditis elegans fer-1. It encodes a predicted cytosolic protein (of 1,230 aa) with three C2 domains and a single carboxy-terminal transmembrane domain. The sequence homologies and predicted structure of otoferlin, the protein encoded by OTOF, suggest its involvement in vesicle membrane fusion. In the inner ear, the expression of the orthologous mouse gene, mainly in the sensory hair cells, indicates that such a role could apply to synaptic vesicles.

BBS10 encodes a vertebrate-specific chaperonin-like protein and is a major BBS locus

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.

X-linked transposition of the great arteries and incomplete penetrance among males with a nonsense mutation in ZIC3

We report on a Lebanese family in which two maternal cousins suffered and died very early in life from cardiac malformations. Both presented with a transposition of the great arteries associated with one or several other cardiac defects. Various minor midline defects were also observed, but there were no situs abnormalities other than a persistent left superior vena cava in one. A maternal uncle of these two babies was born cyanotic and died on the third post-natal day. Analysis of the ZIC3 gene, revealed the presence of a mutation in the second exon leading to a truncation of the protein. Surprisingly, another maternal uncle of the two affected cousins also had the mutation but was not clinically affected. To our knowledge, this is the first instance of incomplete penetrance in a male for a mutation in a chromosome X gene.

The molecular basis of familial hypercholesterolemia in Lebanon: spectrum of LDLR mutations and role of PCSK9 as a modifier gene.

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.

Autosomal recessive non-syndromic hearing loss in the Lebanese population: prevalence of the 30delG mutation and report of two novel mutations in the connexin 26 (GJB2) gene

Editor—The most common sensory deficit in humans is hearing loss, affecting 1 in 1000 children, with approximately half of the cases having a genetic cause. The majority of these genetic causes are non-syndromic, of which approximately 75% have an autosomal recessive mode of inheritance.1 So far, nearly 30 genes that cause non-syndromic recessive deafness (NSRD) have been located (for review see http://dnalab-www.uia.ac.be/dnalab/hhh). The loci corresponding to NSRD are designated DFNB, with a number corresponding to the chronology of their localisation. The first locus, DFNB1 (MIM 220290), located on chromosome 13q11-12,2 has been shown to be responsible for nearly half of NSRD owing to mutations in the gene encoding the gap junction protein connexin 26 ( GJB2 ) (MIM 121011).3 4 One mutation, 30delG (also referred to as 35delG), accounts for the majority of mutations in this gene in some ethnic groups,3-8 while it is rarer in others.9-15 The geographical position of Lebanon, a small country of 10 500 km2 on the eastern shores of the Mediterranean sea, has made it a historical crossroads between Asia, Africa, and Europe. As a consequence, the Lebanese population shows a wide genetic diversity, with no less than 17 ethno-religious communities. Today, the population is approximately 4 million people, with a world wide diaspora estimated at 15 million. In Lebanon, consanguineous marriages are still frequent (from 10 to 30%), favouring the incidence of autosomal recessive diseases,16 such as haemoglobinopathies, sickle cell anaemia, familial Mediterranean fever, congenital hypothyroidism, cystic fibrosis, and deafness. The purpose of this study is to summarise the different NSRD loci found in a case series of Lebanese families and to determine the carrier frequency of the 30delG mutation in selected Lebanese subjects. Forty eight multiplex Lebanese families with non-syndromic congenital moderate to profound deafness, from various …

Pitfalls of homozygosity mapping: an extended consanguineous Bardet-Biedl syndrome family with two mutant genes (BBS2, BBS10), three mutations, but no triallelism

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).

A sensorineural progressive autosomal recessive form of isolated deafness, DFNB13, maps to chromosome 7q34-q36

Deafness is the most frequent sensorineural defect in children. The vast majority of the prelingual forms of isolated deafness are highly genetically heterogeneous with an autosomal recessive mode of inheritance. Using linkage analysis, we have mapped the gene responsible for a severe progressive sensorineural hearing loss, DFNB13, segregating in a large consanguineous family living in an isolated region in northern Lebanon. A maximum lod score of 4.5 was detected for markers D7S661–D7S498. Recombination events and homozygosity mapping by descent define a 17 cM gene interval in the chromosome region 7q34-q36, between the markers D7S2468/D7S2505, on the proximal side, and D7S2439, on the distal side.

Familial Mediterranean Fever: association of elevated IgD plasma levels with specific MEFV mutations

Familial Mediterranean Fever (FMF) is a recessively inherited disorder, characterized by episodic fever, abdominal and arthritic pain, as well as other forms of inflammation. Some FMF patients present higher IgD serum levels, and it is not yet known whether such an elevation is related to specific genotypes or correlated with a specific phenotype. In order to evaluate the association between known FMF-related mutations and IgD levels in confirmed patients, as well as the correlation between those levels and the presence of specific clinical signs, genotypic analysis and IgD plasma measurements were performed for 148 Lebanese and Jordanian FMF patients. Most common mutational patterns were M694V heterozygotes (19%) and homozygotes (17%), and V726A heterozygotes (18%) and homozygotes (5%), with an additional 11% combining both mutations. Twenty-one patients had higher IgD levels (superior to 100 μg/ml). The risk for higher IgD levels was significantly associated with M694V homozygote status (OR = 6.25) but not with heterozygotic one (OR = 1). Similarly, the risk for higher IgD was also found with V726A homozygotes (OR = 2.2) but not with heterozygotes (OR = 1.05). The use of colchicine was not statistically associated with IgD levels. Clinically, hyper IgD was also found significantly associated with arthritis (OR = 18). Thus, homozygotic status for M694V, and to a lesser extent V726A, is associated with increased risk for higher IgD plasma levels, regardless of colchicine use. Elevated IgD plasma levels are also correlated with the severity of FMF manifestations, and especially with arthritis.

A new autosomal recessive non-progressive congenital cerebellar ataxia associated with mental retardation, optic atrophy, and skin abnormalities (CAMOS) maps to chromosome 15q24-q26 in a large consanguineous Lebanese Druze family

Congenital cerebellar ataxias are a heterogeneous group of non-progressive disorders characterized by hypotonia and developmental delay followed by the appearance of ataxia, and often associated with dysarthria, mental retardation, and atrophy of the cerebellum. We report the mapping of a disease gene in a large inbred Lebanese Druze family, with five cases of a new form of non-progressive autosomal recessive congenital ataxia associated with optic atrophy, severe mental retardation, and structural skin abnormalities, to a 3.6-cM interval on chromosome 15q24–15q26.