X-inactivation and marker studies in three families with incontinentia pigmenti: implications for counselling and gene localisation

Familial incontinentia pigmenti (IP) is an X-linked dominant disorder with an extremely variable clinical presentation. Ambiguous diagnosis can compli cate genetic counselling and attempts to refine the gene location in Xq28. Marked skewing of X-inactivation patterns is a hallmark of IP and provides a means for investigating uncertain cases. We have conducted X-inactivation studies in three families where Xq28 marker studies were at odds with the original clinical assessment. The results indicate that no recombination be tween the disease locus and Xq28 loci has occurred and suggest that mosaici sm is responsible for the discrepancy in one family.