MLLT1 and overgrowth syndrome: Mutations in both of these genes are causative of autosomal dominant overgrowth syndromes when found in the germline and the PIK3CA-related overgrowth syndrome predisposes to WT.32,33 With the exception of a small number of rare variants (XPO5, MLLT1, PIK3CA and KRAS), none of these variants were found in Subgroup A tumours.