Stormorken syndrome is a rare genetic disorder (MIM 185070) first reported in 1983 with thrombocytopenia, muscle weakness, asplenia, and miosis caused by a mutation of the stromal interaction molecule 1 (STIM1) gene.¹ The muscle weakness is caused by a myopathy with tubular aggregate formation. We report a family in which both child and mother presented with proximal muscle weakness and thrombocytopenia. Histologic, histochemical, and electron microscopy studies were performed on the muscle specimen. It documented accumulation of tubular aggregates and chronic myopathic changes with dystrophic features. Genetic testing revealed that both mother and son carried a missense mutation of c.326A>G in exon 3 of the STIM1 gene, which is novel for Stormorken syndrome. We suggest that patients with unexplained chronic idiopathic thrombocytopenia and proximal weakness have genetic testing for Stormorken syndrome.