Coffin-Siris syndrome (CSS) is a rare congenital multi-systemic genetic disorder characterized by aplasia or hypoplasia of the distal phalanx or nail of the fifth digit, developmental delay, intellectual disability, coarse facial features, and other variable clinical manifestations. The disease is Coffin-Siris syndrome (MONDO_0015452). Also known as: CSS, dwarfism-onychodysplasia, fifth digit syndrome, short stature-onychodysplasia..