Analysis of disease-causing gene mutation in three Chinese families with congenital inherited cataract / 中华医学遗传学杂志

<p><b>OBJECTIVE</b>To identify the disease-causing gene mutations in three Chinese pedigrees affected with congenital inherited cataract, in ordre to provide genetic counseling and prenatal diagnosis.</p><p><b>METHODS</b>Using exons combined target region capture sequencing chip to screen the candidate disease-causing mutations, Sanger sequencing was used to confirm the disease-causing mutations.</p><p><b>RESULTS</b>Family 1 was polymorphic cataract, family 2 was cerulean cataract, family 3 was coralliform cataract. The inheritance mode of the three pedigrees consisted with autosomal dominant inheritance. In family 1, a nonsense mutation of CRYβB2 gene c.463C>T in exon 6 result in a p.Q155X amino acid change. In family 2, a missense mutation of of CRYGD gene c.43C>T in exon 2 result in a p.R14C amino acid change. In family 3, a missense mutation of CRYGD gene c.70C>A in exon 2 result in a p.P23T amino aid change. No above-mentioned mutations were found in normal individuals.</p><p><b>CONCLUSION</b>The nonsense mutation c.463C>T (p.Q155X) of CRYβB2 gene, the heterozygous mutations c.43C>T(p.R14C) of CRYGD gene and c.70C>A( p.P23T) of CRYGD gene was the disease-causing gene mutation in family 1, 2 and 3 respectively, our results provid genetic counseling and prenatal diagnosis for these three families.</p>

Cataract-causing mutation S228P promotes βB1-crystallin aggregation and degradation by separating two interacting loops in C-terminal domain

β/γ-Crystallins are predominant structural proteins in the cytoplasm of lens fiber cells and share a similar fold composing of four Greek-key motifs divided into two domains. Numerous cataract-causing mutations have been identified in various β/γ-crystallins, but the mechanisms underlying cataract caused by most mutations remains uncharacterized. The S228P mutation in βB1-crystallin has been linked to autosomal dominant congenital nuclear cataract. Here we found that the S228P mutant was prone to aggregate and degrade in both of the human and E. coli cells. The intracellular S228P aggregates could be redissolved by lanosterol. The S228P mutation modified the refolding pathway of βB1-crystallin by affecting the formation of the dimeric intermediate but not the monomeric intermediate. Compared with native βB1-crystallin, the refolded S228P protein had less packed structures, unquenched Trp fluorophores and increased hydrophobic exposure. The refolded S228P protein was prone to aggregate at the physiological temperature and decreased the protective effect of βB1-crystallin on βA3-crystallin. Molecular dynamic simulation studies indicated that the mutation decreased the subunit binding energy and modified the distribution of surface electrostatic potentials. More importantly, the mutation separated two interacting loops in the C-terminal domain, which shielded the hydrophobic core from solvent in native βB1-crystallin. These two interacting loops are highly conserved in both of the N- and C-terminal domains of all β/γ-crystallins. We propose that these two interacting loops play an important role in the folding and structural stability of β/γ-crystallin domains by protecting the hydrophobic core from solvent access.

Mutation analysis of CRYBB1 gene and prenatal diagnosis for a Chinese kindred featuring autosomal dominant congenital nuclear cataract / 中华医学遗传学杂志

<p><b>OBJECTIVE</b>To perform mutation screening and prenatal diagnosis for a five-generation Chinese pedigree with autosomal dominant congenital nuclear cataract from Henan province by DNA sequencing.</p><p><b>METHODS</b>Blood samples were taken from the family members. Four candidate genes (CRYBA1/A3, CRYBB1, CRYBB2 and CRYGD) were screened for mutations using direct sequencing. Prenatal genetic diagnosis was provided for a fetus at early gestation through chorionic villus sampling.</p><p><b>RESULTS</b>A missense mutation, c.387C to A, was detected in exon 4 of the CRYBB1 gene in all of the patients. The mutation has resulted in a p.S129R transversion. The same mutation was not found in the fetus of the proband, who was confirmed to be healthy by one-year follow-up.</p><p><b>CONCLUSION</b>A missense mutation p.S129R of the CRYBB1 gene probably underlies the autosomal dominant congenital nuclear cataract in this pedigree. Detection of the mutation also facilitated prenatal genetic testing for the family.</p>

A missense mutation S228P in the CRYBB1 gene causes autosomal dominant congenital cataract / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Congenital cataract is a highly heterogeneous disorder at both the genetic and phenotypic levels. This study was conducted to identify disease locus for autosomal dominant congenital cataracts in a four generation Chinese family.</p><p><b>METHODS</b>Family history and clinical data were recorded. All the members were genotyped with microsatellite markers which are close to the known genetic loci for autosomal congenital cataracts. Two-point Lod scores were obtained using the MLINK of the LINKAGE program package (ver 5.1). Candidate genes were amplified by polymerase chain reaction (PCR) and direct cycle sequencing.</p><p><b>RESULTS</b>The maximum Lod score of Zmax-2.11 was obtained with three microsatellite markers D22S258, D22S315, and D22S1163 at recombination fraction theta=0. Haplotype analysis showed that the disease gene was localized to a 18.5 Mbp region on chromosome 22 flanked by markers D22S1174 and D22S270, spanning the beta-crystallin gene cluster. A c.752T-->C mutation in exon 6 of CRYBB1 gene, which resulted in a heterozygous S228P mutation in predicted protein, was found to cosegregate with cataract in the family.</p><p><b>CONCLUSIONS</b>This study identified a novel mutation in CRYBB1 gene in a Chinese family with autosomal dominant congenital cataract. These results provide strong evidence that CRYBB1 is a pathogenic gene for congenital cataract.</p>