CONCLUSIVE EVIDENCE FOR A DISTINCT CONGENITAL STATIONARY NIGHT BLINDNESS LOCUS IN XP21.1

X linked congenital stationary night blindness (CSNBX) is a non-progre ssive retinal disorder characterised by decreased visual acuity and di sturbance of night vision. CSNBX appears to be not only clinically but also genetically heterogeneous. On studying a single large family, we recently suggested the presence of a distinct locus for CSNBX in Xp21 .1. Here, we describe the results of a linkage analysis in another lar ge CSNBX family, which confirms this finding. Thus, the data presented here provide conclusive evidence for a distinct CSNBX locus in Xp21.1 , closely linked to the X linked retinitis pigmentosa type 3 gene. The results combined with other published results indicate the order 1110 ,CSNBX1,XLRP3)-DXS7-(CSNBX2,XLRP2)-DXS14-Xcen.