αA-crystallin R49Cneo mutation influences the architecture of lens fiber cell membranes and causes posterior and nuclear cataracts in mice

<p>Abstract</p> <p>Background</p> <p>αA-crystallin (CRYAA/HSPB4), a major component of all vertebrate eye lenses, is a small heat shock protein responsible for maintaining lens transparency. The R49C mutation in the αA-crystallin protein is linked with non-syndromic, hereditary human cataracts in a four-generation Caucasian family.</p> <p>Methods</p> <p>This study describes a mouse cataract model generated by insertion of a neomycin-resistant (neo^r) gene into an intron of the gene encoding mutant R49C αA-crystallin. Mice carrying the neo^rgene and wild-type <it>Cryaa </it>were also generated as controls. Heterozygous knock-in mice containing one wild type gene and one mutated gene for αA-crystallin (WT/R49C^neo) and homozygous knock-in mice containing two mutated genes (R49C^neo/R49C^neo) were compared.</p> <p>Results</p> <p>By 3 weeks, WT/R49C^neomice exhibited large vacuoles in the cortical region 100 μm from the lens surface, and by 3 months posterior and nuclear cataracts had developed. WT/R49C^neomice demonstrated severe posterior cataracts at 9 months of age, with considerable posterior nuclear migration evident in histological sections. R49C^neo/R49C^neomice demonstrated nearly complete lens opacities by 5 months of age. In contrast, R49C mice in which the neo^rgene was deleted by breeding with CreEIIa mice developed lens abnormalities at birth, suggesting that the neo^rgene may suppress expression of mutant R49C αA-crystallin protein.</p> <p>Conclusion</p> <p>It is apparent that modification of membrane and cell-cell interactions occurs in the presence of the αA-crystallin mutation and rapidly leads to lens cell pathology <it>in vivo</it>.</p

Congenital cataract and macular hypoplasia in humans associated with a de novo mutation in CRYAA and compound heterozygous mutations in P

BACKGROUND: An isolated form of congenital cataract associated with macular hypoplasia and a generally hypopigmented fundus in infancy was observed in a German family. To test the hypothesis that a de-novo mutation had occurred in one of the parental germ lines, a functional candidate gene approach was applied. METHODS: The family was carefully examined by a senior paediatric ophthalmologist according to routine procedures (slit lamp, funduscopy, ERG). Blood was taken from the proband and his parents, genomic DNA was isolated and some candidate genes for cataract (CRYAA, CRYBB2, GJA8) or macular hypoplasia (OA1, P) or both (PAX6) were analyzed. RESULTS: The proband showed bilateral cataracts at the age of 4 months; the fundus appeared pale, the optic disc grayish, and macular reflexes were absent. After cataract surgery, the nystagmus persisted, and a control ERG at age 9 years showed essentially normal scotopic and photopic wave forms. An infectious aetiology as well as galactosemia were excluded. However, a heterozygous mutation was found in the proband in exon 1 of CRYAA (62 C-->T), which leads to an exchange from Arg to Leu at amino acid position 21 (R21L). This sequence alteration was not found in the parents and in 96 randomly selected DNA samples from ophthalmologically normal individuals of the KORA S4 study population. In addition, two heterozygous mutations in P were identified (R419Q and A481T); one of both was present in each of the unaffected parents. CONCLUSION: Based upon the unique finding of the mutation and the expression of CRYAA in the lens, this R21L mutation in the CRYAA is considered to be causative for the dominant cataract phenotype. Moreover, the macular hypoplasia has to be considered a concerted interaction with compound heterozygous mutations in the P gene manifesting a mild form of oculocutaneous albinism. Nevertheless, this combination is rare and future studies will focus on identifying similar phenotypes