Genetic and allelic heterogeneity of Cryg mutations in eight distinct forms of dominant cataract in the mouse.

Abstract

The purpose of this study was the characterization of eight new dominant cataract mutations. Lenses of mutant mice were described morphologically and histologically. Each mutation was mapped by linkage studies. The candidate genes (the Cryg gene cluster and the closely linked Cryba2 gene) were sequenced. Molecular analysis confirmed all mutations in Cryg genes. Five mutations lead to amino acid exchanges, two are due to premature stop codons, and one is a 10-bp deletion in the Cryge gene. Morphologically, mutant carriers expressed nonsyndromic cataracts, ranging from diffuse lenticular opacities (Crygd(ENU910) and Cryge(ENU449)), to dense nuclear and subcortical opacity (Crygd(K10), Crygc(MNU8), Cryge(Z2), Crygd(ENU4011), and Cryge(ADD15306)), to dense nuclear opacity and ruptured lenses (Cryga(ENU469)). Results of histologic analyses correlate well with the severity of lens opacity, ranging from alterations in the process of secondary fiber nucleus degradation to lens vacuoles, fiber degeneration, and disruption of the lens capsule. In total, 20 mutations have been described that affect the Cryg gene cluster: Nine mutations affect the Cryge gene, but only one affects the Crygb or Crygf genes. No mutation was observed in the closely linked Cryba2. Two mutations occur at the same site in the Crygd and Cryge genes (Leu45-->Pro). The unequal distribution of mutations suggests hot spots in the Cryg genes. The overall high number of mutations in these genes demonstrates their central role in the maintenance of lens transparency.