RGS6: a novel gene associated with congenital cataract, mental retardation, and microcephaly in a Tunisian family.

PURPOSE: The object of this study is to identify the underlying genetic defect in a consanguineous Tunisian family affected with autosomal recessive congenital cataract associated with mental retardation and microcephaly. METHODS: A whole-genome scan was performed with polymorphic microsatellites in the axiom data for the screened members. Homozygous regions were analyzed with integrated Systems Tool for Eye gene Discovery (iSyTE), to identify candidate genes with lens-enriched expression that were potentially associated with cataract. Then we screened for mutations by direct sequencing. Structure and function of the mutant gene were analyzed by bioinformatics analysis. RESULTS: Using whole-genome scanning, we identified six runs of homozygosity shared among affected members of the studied family. Analysis of these regions by iSyTE allowed us to select 3 genes (RGS6, PCNX, and P4HA1) according to their expression in 3 critical stages of lens development. Upon screening for mutations by sequencing analysis, we found a novel mutation in RGS6, the splice-acceptor variant c.1369-1G>C that was not previously reported in congenital cataract phenotypes. CONCLUSIONS: Our study identified a new gene to be included in the large spectrum of cataract-associated genes. Importantly, the study demonstrated that, in addition to lens-enriched genes that exhibit high expression levels, genes identified by iSyTE that are highly lens-enriched but have lower absolute expression may also represent candidates for potential function in the lens.

Molecular analysis of the PAX6 gene for aniridia and congenital cataracts in Tunisian families.

The aim of this study was to identify the genetic defect that is responsible for aniridia and congenital cataracts in two Tunisian families. Sequencing of the PAX6 gene in family F1 detected a novel c.265C>T transition in exon 6. In family F2, the previously described c.718C>T mutation in PAX6 was detected in the four affected members. This study adds new mutation to those previously reported in PAX6, providing further evidence for the genetic and phenotypic heterogeneity in individuals with aniridia ocular malformations.

Absence of mutations in four genes encoding for congenital cataract and expressed in the human brain in Tunisian families with cataract and mental retardation.

BACKGROUND: To identify the genetic defect associated with autosomal recessive congenital cataract (ARCC), mental retardation (MR) and ARCC, MR and microcephaly present in most patients in four Tunisian consanguineous families. METHODS: We screened four genes implicated in congenital cataract by direct sequencing in two groups of patients; those affected by ARCC associated to MR and those who presented also microcephaly. Among its three genes PAX6, PITX3 and HSF4 are expressed in human brain and one gene LIM2 encodes for the protein MP20 that interact with the protein galectin-3 expressed in human brain and plays a crucial role in its development. All genes were screened by direct sequencing in two groups of patients; those affected by ARCC associated to MR and those who presented also microcephaly. RESULTS: We report no mutation in the four genes of congenital cataract and its flanking regions. Only variations that did not segregate with the studied phenotypes (ARCC associated to MR, ARCC associated with MR and microcephaly) are reported. We detected three intronic variations in PAX6 gene: IVS4 -274insG (intron 4), IVS12 -174G>A (intron12) in the four studied families and IVS4 -195G>A (intron 4) in two families. Two substitutions polymorphisms in PITX3 gene: c.439 C>T (exon 3) and c.930 C>A (exon4) in one family. One intronic variation in HSF4 gene: IVS7 +93C>T (intron 7) identified in one family. And three intronic substitutions in LIM2 gene identified in all four studied families: IVS2 -24A>G (intron 2), IVS4 +32C>T (intron 4) and c.*15A>C (3'-downstream sequence). CONCLUSION: Although the role of the four studied genes: PAX6, PITX3, HSF4 and LIM2 in both ocular and central nervous system development, we report the absence of mutations in all studied genes in four families with phenotypes associating cataract, MR and microcephaly.

The first missense mutation of NHS gene in a Tunisian family with clinical features of NHS syndrome including cardiac anomaly.

Nance-Horan Syndrome (NHS) or X-linked cataract-dental syndrome is a disease of unknown gene action mechanism, characterized by congenital cataract, dental anomalies, dysmorphic features and, in some cases, mental retardation. We performed linkage analysis in a Tunisian family with NHS in which affected males and obligate carrier female share a common haplotype in the Xp22.32-p11.21 region that contains the NHS gene. Direct sequencing of NHS coding exons and flanking intronic sequences allowed us to identify the first missense mutation (P551S) and a reported SNP-polymorphism (L1319F) in exon 6, a reported UTR-SNP (c.7422 C>T) and a novel one (c.8239 T>A) in exon 8. Both variations P551S and c.8239 T>A segregate with NHS phenotype in this family. Although truncations, frame-shift and copy number variants have been reported in this gene, no missense mutations have been found to segregate previously. This is the first report of a missense NHS mutation causing NHS phenotype (including cardiac defects). We hypothesize also that the non-reported UTR-SNP of the exon 8 (3'-UTR) is specific to the Tunisian population.

Absence of PITX3 mutation in a Tunisian family with congenital cataract and mental retardation.

PURPOSE: The PITX3 (pituitary homeobox 3) gene encodes for a homeobox bicoid-like transcription factor. When one allele is mutated, it leads to dominant cataract and anterior segment mesenchymal dysgenesis in humans. When both copies are mutated, homozygous mutation contributes to microphtalmia with brain malformations. In the current study, a family with autosomal recessive congenital cataract (ARCC) associated with mental retardation (MR) was examined to identify PITX3 mutations. METHODS: Sequencing of the PITX3 gene was performed on two affected and three unaffected members of the studied Tunisian family. The results were analyzed with Sequencing Analysis 5.2 and SeqScape. RESULTS: No mutation in the four exons of PITX3 was revealed. Two substitution polymorphisms, c.439C>T and c.930C>A, were detected in exons 3 and 4, respectively. These alterations did not segregate with the disease. CONCLUSIONS: Although PITX3 was shown to be essential to normal embryonic eye and brain development in vertebrates, we report the absence of PITX3 mutations in a family presenting congenital cataract and mental retardation.