Thrombocythemia, X-Linked

For a general phenotypic description and a discussion of genetic heterogeneity of thrombocythemia, see THCYT1 (187950).

Clinical Features

Stuhrmann et al. (2001) reported a Bedouin Arab family consisting of 4 brothers, aged 4 to 8 years, who had either sustained markedly elevated (greater than 1,000 x 10(9) per liter) or moderately elevated (greater than 500 x 10(9) per liter) platelet counts, 2 healthy sisters, and their first-cousin parents, who had normal platelet counts. The 4 brothers with familial thrombocytosis had normal plasma thrombopoietin levels and did not present with any thrombotic or hemorrhagic complications. The intron 3 mutation in thrombopoietin (THPO; 600044.0001) was not identified in any of the sibs. In addition, segregation analysis using a polymorphic CA marker revealed completely discordant THPO alleles among the affected brothers. In the 2 children with the highest platelet counts, minimal liver enlargement and mild to moderate splenomegaly was manifest.

Inheritance

Stuhrmann et al. (2001) stated that although parental consanguinity could argue for autosomal recessive inheritance, they considered X-linked recessive inheritance more likely.