CLINICAL CHARACTERISTICS: Beckwith-Wiedemann syndrome (BWS) is a growth disorder variably characterized by macroglossia, hemihyperplasia, omphalocele, neonatal hypoglycemia, macrosomia, embryonal tumors (e.g., Wilms tumor, hepatoblastoma, neuroblastoma, and rhabdomyosarcoma), visceromegaly, adrenocortical cytomegaly, kidney abnormalities (e.g., medullary dysplasia, nephrocalcinosis, and medullary sponge kidney), and ear creases / posterior helical ear pits. BWS is considered a clinical spectrum, in which affected individuals may have many or only one or two of the characteristic clinical features. Although most individuals with BWS show rapid growth in late fetal development and early childhood, growth rate usually slows by age seven to eight years. Adult heights are typically within the normal range. Hemihyperplasia (also known as lateralized overgrowth) is often appreciated at birth and may become more or less evident over time. Hemihyperplasia may affect segmental regions of the body or selected organs and tissues. Hemihyperplasia may be limited to one side of the body (ipsilateral) or involve opposite sides of the body (contralateral). Macroglossia is generally present at birth and can obstruct breathing or interfere with feeding in infants. Neonatal hypoglycemia occurs in approximately 50% of infants with BWS; most episodes are mild and transient. However, in some cases, persistent hypoglycemia due to hyperinsulinism may require consultation with an endocrinologist for therapeutic intervention. With respect to the increased risk for embryonal tumor development, the risk for Wilms tumor appears to be concentrated in the first seven years of life, whereas the risk for developing hepatoblastoma is concentrated in the first three to four years of life. Cognitive and neurobehavioral development is usually normal. After childhood, prognosis is generally favorable, although some adults experience issues requiring medical management (e.g., for renal or skeletal concerns). DIAGNOSIS/TESTING: The clinical diagnosis of BWS can be established in a proband who has two tier 1 characteristic clinical findings OR one tier 1 and one tier 2 clinical finding. A diagnosis can also be established in a proband with at least one tier 1 or tier 2 clinical finding AND either: A constitutional epigenetic or genomic alteration leading to an abnormal methylation pattern at 11p15.5 known to be associated with BWS; OR. A copy number variant of chromosome 11p15.5 known to be associated with BWS; OR. A heterozygous BWS-causing pathogenic variant in . MANAGEMENT: : Hypoglycemia is treated with oral feeding if it is mild or with glucose supplementation. Hyperinsulinism is treated with standard pharmacotherapy per endocrinologist; partial pancreatectomy may be considered in those with persistent hypoglycemia who are unresponsive to pharmacologic treatment. Feeding and/or respiratory support (sometimes requiring intubation at birth or tracheostomy for severe respiratory insufficiency) may be needed for those with macroglossia and/or upper airway obstruction. Tongue reduction surgery may be considered for this and other indications. Standard treatment is recommended for omphalocele per pediatric surgeon. A shoe lift may be considered in those with a leg length discrepancy. Epiphysiodesis prior to epiphyseal closure in early puberty may be considered in instances with leg length discrepancy >2 cm; alternatively, leg lengthening of the shorter leg may be considered. For those with hemihyperplasia of the face, referral to a craniofacial center for assessment and potential treatments may be considered. If present, standard treatment is recommended for speech delay/impediment, neoplasia, congenital heart defects, and hypercalciuria / kidney anomalies. Perspectives on screening for malignant tumors in childhood differ based on local, national, and international practices. In North America, proactive tumor screening is recommended when the risk of tumor development exceeds 1%. In many European countries, proactive tumor screening protocols are typically undertaken when the risk of tumor development exceeds 5% and are based on molecular mechanism. For most BWS molecular subtypes, tumor screening consists of abdominal ultrasound with views of the liver, adrenal glands, and kidneys every three months until age four years followed by kidney ultrasound only every three months from age four to seven years. Serum alpha-fetoprotein (AFP) levels are performed every three months until age four years. Physical exam by a pediatrician, geneticist, or pediatric oncologist twice a year is also recommended. Proposed screening for neuroblastoma in children with a heterozygous pathogenic variant in includes abdominal ultrasound, urine vanillylmandelic acid and homovanillic acid, and chest radiograph every three months until age six years, then every six months until age ten years. includes measurement of growth parameters, assessment for signs/symptoms of sleep apnea, and monitoring of developmental progress / educational needs at each visit; pre-feed serum glucose level per endocrinologist recommendations in neonates and infants with a history of hypoglycemia/hyperinsulinism or random serum glucose level in neonates and infants with signs/symptoms consistent with hypoglycemia; consideration of blood pressure measurements and measurement of urinary calcium-to-creatinine ratio to screen for occult nephrocalcinosis annually or biannually; consideration of kidney ultrasound to identify findings such as nephrocalcinosis and medullary sponge kidney annually between age eight years and mid-adolescence and periodically in adulthood; assessment of hemihyperplasia and leg length discrepancy at each visit at least until skeletal maturity; dental evaluation with low threshold for orthodontic evaluation as clinically indicated. GENETIC COUNSELING: BWS is associated with abnormal expression of imprinted genes in the BWS critical region. Reliable recurrence risk assessment requires identification of the genetic mechanism in the proband that underlies the abnormal expression of imprinted genes in the BWS critical region. While the majority of families have a recurrence risk of less than 1%, certain underlying genetic mechanisms (e.g., pathogenic variants and copy number variants involving 11p15) may be associated with a recurrence risk as high as 50% depending on the sex of the transmitting parent and the specific alteration. In families with recurrence of BWS, maternally inherited pathogenic variants account for approximately 40% of genetic alterations and paternally or maternally inherited copy number variants account for approximately 9% of genetic alterations. Of note, some individuals with BWS have methylation alterations in the 11p15 imprinted domain as well as in other imprinted loci. For these individuals review of the maternal history should be undertaken for unexplained spontaneous abortion, hydatidiform moles, or a sib with BWS or another imprinting disorder (e.g., Silver-Russell syndrome); in such cases, a homozygous or heterozygous pathogenic variant in maternal effect gene in the mother's genome may confer a significant recurrence risk. If a genomic variant involving chromosome 11p15.5 (i.e., a cytogenetically visible duplication, inversion, or translocation), copy number variant of 11p15.5, or a pathogenic variant has been identified in the proband, prenatal testing via analysis of fetal DNA from samples obtained by chorionic villus sampling (CVS) or amniocentesis is possible. Preimplantation genetic testing is possible for a familial pathogenic variant and may be possible for some familial genomic variants. For evaluation of fetal methylation status, DNA extracted from amniotic fluid is currently felt to provide the most reliable tissue source, although false negative findings have been reported. Tissue obtained via CVS for prenatal testing for methylation status does not yield reliable results. Genetic counseling should emphasize the potential limitations of prenatal testing for epigenetic alterations.