[Type I lattice corneal dystrophy. Clinical and molecular genetic study of a large family]

Lattice corneal dystrophy type I is one of the frequent forms of stromal dystrophies following autosomal dominant inheritance. The beta-IG-h3 gene encoding keratoepithelin on the long arm of chromosome 5 has recently been described as disease gene for lattice corneal dystrophy type I as well as for three other corneal dystrophies with autosomal dominant pattern of inheritance.

Ten family members in three generations of a large family with autosomal dominant lattice corneal dystrophy were analyzed clinically by slit-lamp biomicroscopy. Mutation analysis in the beta-IG-h3 gene was carried out at the mRNA level by RT-PCR and cDNA sequencing.

A heterozygous single-base substitution (417C-->T) in exon 4 of the beta-IG-h3 gene was detected predicting the replacement of arginine-124 by cysteine. Analysis of 10 family members showed perfect cosegregation of the mutation and lattice corneal dystrophy type I. The investigation excluded this mutation in one family member previously classified as potentially affected.

The investigation confirmed autosomal dominant inheritance with complete penetrance in the family described. The mutation 417C-->T has already been found earlier in another family of different geographic origin. These results suggest a mutation hot spot at position 417. In addition, no evidence of genetic heterogeneity of lattice corneal dystrophy type I was detected. Molecular genetic analysis (in conjunction with genetic counselling) therefore may be useful in routine diagnostics as the confirmation of the diagnosis by histological examination is possible only after keratoplasty. The common pathomechanism in lattice corneal dystrophy type I may facilitate development of new therapeutic concepts; the easy accessibility of the target organ may provide new possibilities e.g. for gene therapy.