The GJA8 allele encoding CX50I247M is a rare polymorphism, not a cataract-causing mutation

[摘要] Purpose: The aim of this study was thegenetic, cellular, and physiological characterization of a connexin50(CX50) variant identified in a child with congenital cataracts. Methods: Lens material from surgery wascollected and used for cDNA production. Genomic DNA was prepared fromblood obtained from the proband and her parents. PCR amplified DNAfragments were sequenced and characterized by restriction digestion.Connexin protein distribution was studied by immunofluorescence intransiently transfected HeLa cells. Formation of functional channelswas assessed by two-microelectrode voltage-clamp in cRNA-injected Xenopusoocytes. Results: Ophthalmologic examinationshowed that the proband suffered from bilateral white, diffusecataracts, but the parents were free of lens opacities. Directsequencing of the PCR product produced from lens cDNA showed that theproband was heterozygous for a G>T transition at position 741 of theGJA8 gene, encoding the exchange of methionine for isoleucine atposition 247 of CX50 (CX50I247M). The mutation was confirmed in thegenomic DNA, but it was also present in the unaffected mother. Whenexpressed in HeLa cells, both wild type CX50 and CX50I247M formed gapjunction plaques. Both CX50 and CX50I247M induced gap junctionalcurrents in pairs of Xenopus oocytes. Conclusions: Although the CX50I247Msubstitution has previously been suggested to cause cataracts, ourgenetic, cellular, and electrophysiological data suggest that thisallele more likely represents a rare silent, polymorphic variant.

[学科分类] 生物化学/生物物理