ClinVar

In affected members of a 3-generation family with thrombocytopenia-6 (THC6; 616937), Turro et al. (2016) identified a heterozygous c.1579G-A transition in the SRC gene, resulting in a glu527-to-lys (E527K) substitution at a conserved residue in the kinase domain. The mutation, which was found by exome sequencing and confirmed by Sanger sequencing, segregated with the disorder in the family and was not found in the ExAC database or in 2,974 in-house control subjects. In vitro functional expression assays showed that the mutation resulted in high kinase activity compared to wildtype, consistent with a dominant gain of function. Immunoblot analysis of patient cells showed increased levels of active SRC and overall increased tyrosine phosphorylation compared to controls. Transfection of the mutation into control blood stem cells caused defective megakaryopoiesis associated with increased overall tyrosine phosphorylation in megakaryocytes. Compared with control conditions, more megakaryocytes were immature and had defects in proplatelet formation, with alterations in the actin cytoskeleton and podosome structures when adhered to fibrinogen. These abnormalities resembled those found in patient bone marrow biopsies and could be rescued using an SRC inhibitor. Expression of the mutation in zebrafish embryos resulted in abnormal early primitive hematopoiesis, thrombocytopenia, and smaller bones compared to controls.