Variable expression of tapetoretinal degeneration in northern Sweden.

In the county of Västerbotten in northern Sweden, 20 families with 50 diagnosed cases and 53 sporadic cases of tapetoretinal degenerations (TRD), including retinitis pigmentosa (RP), were ascertained. The familial and sporadic cases were traced genealogically as far back as was possible. Ancestors born before 1890 (n = 12,033) were registered on a PC. The analysis of data showed that 7 families (20 cases) and 21 sporadic cases could be traced to ancestors in a parish in the northern part of the county. The results suggest, in that parish, a gene source of an autosomal recessive gene causing TRD, with varying phenotypic expression, including variants of RP.