Familial clustering of systemic lupus erythematosus in the cayman islands.

OBJECTIVE: To describe the unusual clustering of systemic lupus erythematosus (SLE) in a family from the Cayman Islands. METHOD: An observational retrospective study of SLE was done following an index case of mixed connective tissue disease in a 51-year old West Indian woman of African descent. Her two daughters of the same father, who is of Cayman Islands origin, were also diagnosed with SLE. A family tree was subsequently drawn up to 1890 to identify other cases in the same family. RESULTS: There were 13 cases identified and all occurred between the 6th and the 8th generation. A family tree linked all cases to a man from the Cayman Islands who died in 1890. The nine cases with full medical records showed eight females and one male (8:1). The mean age at diagnosis was 29 years; polyarthritis occured in all nine patients (100%), kidney involvement in 6/9 (66.6%), skin rash in 6/9 (66.6%), pleuritis and pericarditis in 6/9 (66.6%) and anaemia in 6/9 (66.6%). The autoantibodies were mainly ANA in all patients (100%) and anti-dsDNA in 8/9 (88.8%). CONCLUSION: The unusual extensive familial clustering in this study represents the first to be described in a West Indian population where SLE is most prevalent and may suggest a genetic predisposition.

Homozygosity mapping to the USH2A locus in two isolated populations.

Usher syndrome is a group of autosomal recessive disorders characterised by progressive visual loss from retinitis pigmentosa and moderate to severe sensorineural hearing loss. Usher syndrome is estimated to account for 6-10% of all congenital sensorineural hearing loss. A gene locus in Usher type II (USH2) families has been assigned to a small region on chromosome 1q41 called the UHS2A locus. We have investigated two families with Usher syndrome from different isolated populations. One family is a Norwegian Saami family and the second family is from the Cayman Islands. They both come from relatively isolated populations and are inbred families suitable for linkage analysis. A lod score of 3.09 and 7.65 at zero recombination was reached respectively in the two families with two point linkage analysis to the USH2A locus on 1q41. Additional homozygosity mapping of the affected subjects concluded with a candidate region of 6.1 Mb. This region spans the previously published candidate region in USH2A. Our study emphasises that the mapped gene for USH2 is also involved in patients from other populations and will have implications for future mutation analysis once the USH2A gene is cloned.

A cerebellar ataxia locus identified by DNA pooling to search for linkage disequilibrium in an isolated population from the Cayman Islands.

A non-progressive recessive cerebellar ataxia was identified in a highly inbred Cayman island population. Cayman cerebellar ataxia is characterized by marked psychomotor retardation, and prominent cerebellar dysfunction manifested by nystagmus, intention tremor, dysarthric speech, and an ataxic gait. In this study, we identify linkage to chromosome 19p 13.3 using pooled DNA samples of affected individuals from an isolated population as PCR template for a genome wide screen with short tandem repeat markers. Our data demonstrate that the DNA pooling approach to identify disease gene loci is feasible using individuals from isolated populations in which kindred relationships are highly complex and exact relationships between all affected individuals are not known. Genetic fine mapping demonstrates that the genetic disease interval is approximately 9 cM, but contained within a small physical region. The existence of multiple individuals that are recombinant with flanking markers indicates that the disease interval can be further narrowed with additional markers.