[Molecular genetic analysis of the BIGH3 gene in lattice type I (Biber-Haab-Dimmer) and granular type II (Avellino) corneal dystrophy: is indirect mutation analysis for hot spots recommended?].

Background: Mutations of the BIGH3 gene were delineated as the underlying gene defect for corneal dystrophy Lattice Type I (CDL1) and corneal dystrophy Avellino type (CDA) in families with different regional provenance. Missense mutations in exon 4 with single base pair substitution which result in amino acid alterations Arg124Cys (CDL1) and ARG124His are described as hot spots. We report on histopathological and molecular genetic investigations in 2 German families and a single patient with CDL1 and CDA.

Method: In 3 affected family members and 1 unaffected family member and in one single patient with CDL1 and in 3 affected family members and 1 unaffected family member of a family with CDA mutation analysis in exon 4 of BIGH3 gene by direct sequencing of genomic DNA from peripheral blood was performed. Histopathological examination of corneal tissue of both index patients was performed after penetrating keratoplasty.

Results: We revealed a heterozygous single base pair substitution 417C-->T in family A and patient B (CDL1) and a heterozygous single base pair substitution 418G-->A in family C (CDA). In all index patient's diagnosis was confirmed by histopathological examination of corneal tissue. The sequencing results were confirmed by restriction digestion with HpyCH4V (NEB; CDL1) restriction endonuclease site and AvaII (NEB; CDA) restriction endonuclease site. The heterozygous 417C-->T transition in family A and patient B alters the amino acid sequence from Arg124Cys while the heterozygous 418G-->A transition in family C alters the amino acid sequence from Arg124His in the keratoepithelin.

Comment: Codon 124 of the BIGH3 gene appears as a mutation hot spot also in German families with CDL1 and CDA. Indirect mutation analysis with restriction digestion is suggested as first step investigation in families with relevant corneal dystrophies. Direct sequencing of all exons is recommended as a second step if there are no results in restriction digestion.