X-Linked Gray Platelet Syndrome Due to a GATA1Arg216Gln Mutation.

Gray Platelet Syndrome (GPS) is characterized by a variable, mild bleeding diathesis, associated with thrombocytopenia and large, agranular, functionally abnormal platelets. While the disorder has been well-described both biochemically and pathologically, to our knowledge, no genetic mutation has been associated with the disease. Most cases are sporadic, with a few sibships and apparent autosomal kindreds reported. In our investigation, the proband is a healthy 1 year-old female whose father and uncle had recently been diagnosed with GPS. The child had a platelet count of 382 x103platelets/μl, comprised of a dimorphic population of normal and large, agranular forms. Her CBC and peripheral blood smear were otherwise unremarkable. We subsequently analyzed four generations of this family. In addition to the proband's father and uncle, several other members had known bleeding tendencies. The symptomatic individuals were invariably males, consistent with a sex-linked pattern of inheritance. Several symptomatic and asymptomatic family members were evaluated by CBC and blood smear. Large, agranular platelets were found in symptomatic males, while obligate carrier females exhibited both normal and abnormal forms. Using a set of fifteen microsatellite markers spanning the X chromosome, a common haplotype was identified in all affected men, their mothers, and their daughters. Aided by the published sequence of the X chromosome, we examined this region for candidate genes. Although the common haplotype between markers GATA144D04 and DXS6797 (Xp11.3-Xq22.3) contains hundreds of genes, only two, GATA1and WAS, have known associations with thrombocytopenia. PCR amplification and sequencing of a 3′ segment of the GATA-1 promoter and the five coding exons of the GATA-1 gene revealed an G759A missense mutation resulting in an Arg216Gln substitution in exon 4 (NCBI RefSeq: NM_002049) that segregated with the phenotype and was present in all obligate carrier females. This mutation has been previously associated with X-linked thrombocytopenia and beta-thalassemia (XLTT), a syndrome characterized by splenomegaly, thrombocytopenia, and imbalanced globin chain synthesis (Balduini et al, Thromb Haemost . 2004; 91:129). Comparison of the ultrastructural characteristics of the platelets in both disorders and a review of literature on both diseases suggests that XLTT, and the associated mutation in GATA1, could represent one genetic origin for GPS. As carrier females generally display a less severe phenotype than affected males, without thrombocytopenia and with subtle dimorphism on smears, it is possible that this mutation may account for some previously reported “sporadic” cases of GPS.