The GJA8 allele encoding CX50I247M is a rare polymorphism, not a cataract-causing mutation.
OBJECTIVE
The aim of this study was the genetic, cellular, and physiological characterization of a connexin50 (CX50) variant identified in a child with congenital cataracts.


METHODS
Lens material from surgery was collected and used for cDNA production. Genomic DNA was prepared from blood obtained from the proband and her parents. PCR amplified DNA fragments were sequenced and characterized by restriction digestion. Connexin protein distribution was studied by immunofluorescence in transiently transfected HeLa cells. Formation of functional channels was assessed by two-microelectrode voltage-clamp in cRNA-injected Xenopus oocytes.


RESULTS
Ophthalmologic examination showed that the proband suffered from bilateral white, diffuse cataracts, but the parents were free of lens opacities. Direct sequencing of the PCR product produced from lens cDNA showed that the proband was heterozygous for a G>T transition at position 741 of the GJA8 gene, encoding the exchange of methionine for isoleucine at position 247 of CX50 (CX50I247M). The mutation was confirmed in the genomic DNA, but it was also present in the unaffected mother. When expressed in HeLa cells, both wild type CX50 and CX50I247M formed gap junction plaques. Both CX50 and CX50I247M induced gap junctional currents in pairs of Xenopus oocytes.


CONCLUSIONS
Although the CX50I247M substitution has previously been suggested to cause cataracts, our genetic, cellular, and electrophysiological data suggest that this allele more likely represents a rare silent, polymorphic variant.
Graw
Jochen
J
Helmholtz Center Munich - German Research Center for Environmental Health, Institute of Developmental Genetics, D-85764 Neuherberg, Germany.
Schmidt
Werner
W
Minogue
Peter J
PJ
Rodriguez
Jessica
J
Tong
Jun-Jie
JJ
Klopp
Norman
N
Illig
Thomas
T
Ebihara
Lisa
L
Berthoud
Viviana M
VM
Beyer
Eric C
EC
D000328:Adult; D000368:Aged; D000483:Alleles; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics*; D001483:Base Sequence; D002386:Cataract / Q000235:genetics*; D017630:Connexins / Q000737:chemistry / Q000235:genetics*; D005136:Eye Proteins / Q000737:chemistry / Q000235:genetics*; D005190:Family; D005260:Female; D017629:Gap Junctions / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D050505:Mutant Proteins; D009154:Mutation / Q000235:genetics*; D010375:Pedigree; D011110:Polymorphism, Genetic; D014162:Transfection; D000099264:Connexin 50
D017630:Connexins; D005136:Eye Proteins; D050505:Mutant Proteins; D000099264:Connexin 50