Huntington's disease: genetic heterogeneity in black African patients.

OBJECTIVE Huntington's disease (HD) has been reported to occur rarely in black patients. A new genetic variant- Huntington's disease-like 2 (HDL2)--occurring more frequently in blacks, has recently been described. The absence of an expanded trinucleotide repeat at the chromosome 4 HD locus was previously regarded as a way of excluding classic HD. The objective of this paper is to describe a number of black patients with genetically proven HD and to review its occurrence in Africa. METHODS Eleven black families (12 subjects), with genetically proven HD, are described: 9 from the Dr George Mukhari Hospital, and 2 from private practice in Tshwane. RESULTS Chorea was present in all 12 patients and cognitive decline in 9. Nine had an age of onset between 30 and 50 years. Six families exhibited expansion of the trinucleotide repeat at the chromosome 4, IT 15 gene (HD), and 5 a junctophilin (JPH3) trinucleotide expansion at chromosome 16 (HDL2). The HDL2 subtype showed a tendency towards a later age of onset. CONCLUSIONS The clinical presentation of the two genotypes (i.e. HD and HDL2) appears to be similar. The actual rate of occurrence of HD in blacks may require re-assessment. Considering the number of Huntington's chorea patients occurring in our area (Garankuwa), the possibility of clustering of the condition arises.