DNA analysis and recombination in X-linked retinitis pigmentosa

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 the disorder shows apparent X linked inheritance but does not show linkage to the RP2 and RP3 regions of the short arm of the X chromosome. The families are also inconsistent with a localisation of the disease gene between DXS164 and DXS28. In one case, reassessment of the family in the light of these results suggested that the family may have an autosomal 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 data alone. Molecular genetics plays an important role in confirming the mode of inheritance and in detecting potential misclassifications, particularly in a group of disorders as heterogeneous as RP. They emphasise that caution is required in genetic counselling of RP families, particularly in the absence of any molecular genetic analysis.

Prenatal exclusion of Norrie's disease

We report on the use of DNA marker probes and linkage analysis to exclude Norrie's disease in the male fetus of a high risk carrier. There are no clinical markers in females carrying the Norrie's disease gene; thus DNA linkage analysis is an essential technique in the management of families 'at-risk' for this severe ophthalmic disease. The principles of DNA linkage are discussed.