Familial keratoconus with cataract: linkage to the long arm of chromosome 15 and exclusion of candidate genes.
OBJECTIVE
Keratoconus and cataract are common causes of visual morbidity. Both conditions show genetic predisposition. The purpose of this study was to map the disease locus in a large three-generation family affected by combined early-onset autosomal dominant anterior polar cataract and clinically severe keratoconus. Uniquely, in this family both disorders were present and fully penetrant in those affected.


METHODS
Thirty members of the family were examined clinically on two occasions, at an interval of 5 years, to establish their phenotypes and determine the progression of the disease. Genomic DNA was extracted from blood samples of 16 affected and 14 unaffected individuals, and typed with more than 350 highly polymorphic microsatellite loci in a genome-wide linkage screen. Markers were amplified by PCR with fluorescently labeled primers and sized with an automated DNA analyser before calculation of lod scores. After linkage was established, several positional candidate genes were assessed by PCR-based DNA sequencing.


RESULTS
The locus for keratoconus with cataract was mapped to a 6.5-Mb region of the long arm of chromosome 15, at 22.33-24.2 between CYP11A and D15S211. The positional and functional candidate genes CTSH, CRABP1, IREB2, and RASGRF1 were excluded as the cause of keratoconus with cataract in this family.


CONCLUSIONS
This is the first report of a family with autosomal dominant inheritance of keratoconus in association with cataract. The causative gene maps to the long arm of chromosome 15 but has not yet been identified.
Hughes
Anne E
AE
Department of Medical Genetics, Queen's University, Belfast City Hospital, Lisburn Road, Belfast BT9 7AB, Northern Ireland, U.K. a.hughes@qub.ac.uk
Dash
Durga P
DP
Jackson
A Jonathan
AJ
Frazer
David G
DG
Silvestri
Giuliana
G
D000293:Adolescent; D000328:Adult; D002386:Cataract / Q000235:genetics* / Q000503:physiopathology; D002874:Chromosome Mapping; D002884:Chromosomes, Human, Pair 15 / Q000235:genetics*; D004247:DNA / Q000032:analysis; D005260:Female; D005799:Genes, Dominant; D008040:Genetic Linkage; D006801:Humans; D007640:Keratoconus / Q000235:genetics* / Q000503:physiopathology; D008297:Male; D018895:Microsatellite Repeats; D010375:Pedigree; D016133:Polymerase Chain Reaction
D004247:DNA