RETINITIS-PIGMENTOSA FAMILIES SHOWING APPARENT X-LINKED INHERITANCE BUT UNLINKED TO THE RP2 OR RP3 LOCI

Three families with retinitis pigmentosa (RP) are described in which t he disorder shows apparent X linked inheritance but does not show link age to the RP2 and RP3 regions of the short arm of the X chromosome. T he families are also inconsistent with a localisation of the disease g ene between DXS164 and DXS28. In one case, reassessment of the family in the light of these results suggested that the family may have an au tosomal dominant form of RP. The remaining two families are consistent with X linkage and suggest the possibility of a new X Linked RP (XLRP ) locus. These families highlight the difficulties in determining the mode of inheritance on the basis of pedigree structure and clinical da ta alone. Molecular genetics plays an important role in confirming the mode of inheritance and in detecting potential misclassifications, pa rticularly in a group of disorders as heterogeneous as RP. They emphas ise that caution is required in genetic counselling of RP families, pa rticularly in the absence of any molecular genetic analysis.