In patient S177 presenting with SM (−3.2 SD), DD, hypotonia and dysmorphic facial features, we identified a heterozygous de novo variant NM_031407.7: c.9208C>T: p.(Arg3070Cys) in HUWE1 and another de novo heterozygous variant NM_015265.4: c.490G>A: p.(Asp164Asn) in the SATB2 gene. This evidence concerns the gene HUWE1 and systemic mastocytosis.