Usher syndrome type I is not linked to D1S81 (pTHH 33): evidence for genetic heterogeneity

Usher syndrome is an autosomal recessive disease associating congenital sensorineural deafness and retinitis pigmentosa. Two clinical forms have been recognized, namely a) congenital and severe (type I) and b) later and moderate (type II). A linkage of the D1S81 probe (THH 33) with the gene for type II has been recently demonstrated by Kimberling et al. 1990. Here, a panel of 29 individuals from 6 kindreds with Usher syndrome type I has been tested for possible allelism at the D1S81 locus. A negative lod-score was found with this probe and close linkage to this region could be excluded. These different results support the view that the clinical heterogeneity in Usher syndrome is accounted for by an obvious genetic heterogeneity.