Analysis of 12,517 inhabitants of a Sardinian geographic isolate reveals that predispositions to thrombocytopenia and thrombocytosis are inherited traits

Background Thrombocytopenia is a common finding in several diseases but almost nothing is known about the prevalence of thrombocytopenia in the general population. We examined the prevalence of thrombocytopenia and determinants of platelet count in a healthy population with a wide age range. Design and Methods We performed a cross-sectional study on 12,517 inhabitants of ten villages (80% of residents) in a secluded area of Sardinia (Ogliastra). Participants underwent a complete blood count evaluation and a structured questionnaire, used to collect epidemiological data. Results We observed a platelet count lower than 150x10(9)/L in 3.2% (2.8-3.6%) of females and 4.8% (4.3-5.4%) of males, with a value of 3.9% (3.6-4.3%) in the entire population. Thrombocytopenia was mild (platelet count: 100-150x10(9)/L), asymptomatic and not associated with other cytopenias or overt disorders in most cases. Its standardized prevalence was quite different in different villages, with values ranging from 1.5% to 6.8%, and was negatively correlated with the prevalence of a mild form of thrombocytosis, which ranged from 0.9% to 4.5%. Analysis of platelet counts across classes of age revealed that platelet number decreased progressively with aging. As a consequence, thrombocytopenia was nearly absent in young people and its prevalence increased regularly during lifetime. The opposite occurred for thrombocytosis. Conclusions Given the high genetic differentiation among Ogliastra villages with "high" and "low" platelet counts and the substantial heritability of this quantitative trait (54%), we concluded that the propensity to present mild and transient thrombocytosis in youth and to acquire Mild thrombocytopenia during aging are new genetic traits.