Meckel or Meckel-Gruber syndrome is a clinically and genetically heterogeneous group of disorders with severe multisystem manifestations. The triad of cystic renal disease, polydactyly (and sometimes syndactyly), and a skull malformation (usually an encephalocele) is considered characteristic of MKS. However, these signs are variable and only about 60% of patients have all three features. Many patients have additional signs such as malformations of the biliary tree, cleft palate (and/or lip), sloping forehead, low-set ears, short neck, low-set ears, ambiguous genitalia, and short, bowed limb bones. Pulmonary hypoplasia is common which, together with kidney and liver disease, is responsible for the poor prognosis of most infants.
Many clinical abnormalities resemble those present in the Smith-Lemli-Opitz syndrome (270400) and in Joubert syndrome (213300).