Laron syndrome is an autosomal recessive disorder characterized by marked short stature that results from failure to generate insulin-like growth factor I (IGF1; 147440) in response to growth hormone (GH; 139250). GH levels are normal or increased. The disorder is caused by dysfunction of the growth hormone receptor. A Laron syndrome-like phenotype associated with immunodeficiency (245590) is caused by a postreceptor defect, i.e., mutation in the STAT5B gene (604260). Patients with mutations in the GHR gene that cause only partial insensitivity to growth hormone have a form of short stature (604271).

Metachondromatosis is characterized by exostoses (osteochondromas), commonly of the hands and feet, and enchondromas of long bone metaphyses and iliac crests (summary by Sobreira et al., 2010).

Mulvihill-Smith syndrome is characterized by premature aging, multiple pigmented nevi, lack of facial subcutaneous fat, microcephaly, short stature, sensorineural hearing loss, and mental retardation. Immunodeficiency may also be a feature. Adult manifestations include the development of tumors, a sleep disorder with severe insomnia, and cognitive decline (summary by Yagihashi et al., 2009).

Bowen-Conradi syndrome (BWCNS) is an autosomal recessive disorder characterized by severely impaired prenatal and postnatal growth, microcephaly, prominent nose with absent glabellar angle, micrognathia, joint abnormalities including flexion contractures, camptodactyly, rocker-bottom feet, and severe psychomotor delay. Most patients do not survive beyond the first year of life as a result of complications associated with reduced mobility and failure to thrive (summary by Armistead et al., 2009).

Multiple congenital anomalies-hypotonia-seizures syndrome-2 (MCAHS2) is an X-linked recessive neurodevelopmental disorder characterized by dysmorphic features, neonatal hypotonia, early-onset myoclonic seizures, and variable congenital anomalies involving the central nervous, cardiac, and urinary systems. Some affected individuals die in infancy (summary by Johnston et al., 2012). The phenotype shows clinical variability with regard to severity and extraneurologic features. However, most patients present in infancy with early-onset epileptic encephalopathy associated with developmental arrest and subsequent severe neurologic disability; these features are consistent with a form of developmental and epileptic encephalopathy (DEE) (summary by Belet et al., 2014, Kato et al., 2014). The disorder is caused by a defect in glycosylphosphatidylinositol (GPI) biosynthesis. For a discussion of genetic heterogeneity of MCAHS, see MCAHS1 (614080). For a discussion of nomenclature and genetic heterogeneity of DEE, see 308350. For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293).