RAP1B and Thrombocytopenia: Although RAP1B is expressed ubiquitously, P1 did not present any associated syndromic features, unlike patients with syndromic thrombocytopenia, who also exhibit neurodevelopmental retardation, growth delay, and congenital birth defects, including cardiovascular, genitourinary, neurologic, and skeletal malformations as well as microcephaly and facial dysmorphia (Table 3) (5, 6).