Simpson-Golabi-Behmel syndrome type 1 (SGBS1) is characterized by pre- and postnatal macrosomia; distinctive craniofacial features (including macrocephaly, coarse facial features, macrostomia, macroglossia, and palatal abnormalities); and commonly, mild-to-severe intellectual disability with or without structural brain anomalies. Other variable findings include supernumerary nipples, diastasis recti / umbilical hernia, congenital heart defects, diaphragmatic hernia, genitourinary defects, and gastrointestinal anomalies. Skeletal anomalies can include vertebral fusion, scoliosis, rib anomalies, and congenital hip dislocation. Hand anomalies can include large hands and postaxial polydactyly. Affected individuals are at increased risk for embryonal tumors including Wilms tumor, hepatoblastoma, adrenal neuroblastoma, gonadoblastoma, hepatocellular carcinoma, and medulloblastoma.

Testicular germ cell tumors (TGCTs) affect 1 in 500 men and are the most common cancer in males aged 15 to 40 in western European populations. The incidence of TGCT rose dramatically during the 20th century. Known risk factors for TGCT include a history of undescended testis (UDT), testicular dysgenesis, infertility, previously diagnosed TGCT, and a family history of the disease. Brothers of men with TGCT have an 8- to 10-fold risk of developing TGCT, whereas the relative risk to fathers and sons is 4-fold. This familial relative risk is much higher than that for most other types of cancer (summary by Rapley et al., 2000). Genetic Heterogeneity of Testicular Germ Cell Tumors A locus for testicular germ cell tumors (TGCT1; 300228) has been identified on chromosome Xq27.

Isolated hemihyperplasia is an abnormality of cell proliferation leading to asymmetric overgrowth of one or more regions of the body. The term 'hemihyperplasia' has replaced the term 'hemihypertrophy' to describe accurately the increase in cell number found in these patients. The incidence of isolated hemihyperplasia is estimated to be 1 in 86,000. Idiopathic hemihypertrophy is associated with increased risk of embryonal cancers in childhood, particularly Wilms tumor (194070) (Shuman et al., 2006). Hoyme et al. (1998) provided an anatomic classification of hemihyperplasia: complex hemihyperplasia is involvement of half of the body, including at least 1 arm and 1 leg; affected parts may be contralateral or ipsilateral. Simple hemihyperplasia is involvement of a single limb. See also facial hemihyperplasia (133900). Although isolated hemihyperplasia is a distinct clinical entity, it can also occur as a feature of overgrowth syndromes, including Beckwith-Wiedemann syndrome (BWS; 130650), neurofibromatosis (NF1; 162200), Proteus syndrome (176920), and Klippel-Trenaunay-Weber syndrome (149000) (Shuman et al., 2006).