The presence of a gene variant causing the amino acid exchange R471C substitution in the gene EWSR1 (EWSR1 binding protein, chromosome 22q12.2, MIM 133450, Gene ID 2130) has been reported, related with FUS (as genes encoding RNA-binding proteins), in a single subject with familial ET from two subsets of ET patients (n = 661) and controls (n = 886) [100]. The gene discussed is FUS; the disease is essential thrombocythemia.