Originally described independently by Williams and Beuren in 1961, Williams syndrome (WS) is a rare genetic condition. The clinical manifestations include a distinct facial appearance, cardiovascular anomalies that may be present at birth or may develop later in life, idiopathic hypercalcemia, and a characteristic neurodevelopmental and behavioral profile.
In virtually all cases of Williams syndrome, haploinsufficiency (loss of 1 of 2 copies) due to a deletion at chromosome band 7q11.23 that involves the elastin gene (ELN) is implicated. Most deletions are not detected through standard karyotyping but rather through fluorescent in situ hybridization (FISH) for a 1.5-Mb deletion (Williams-Beuren syndrome chromosomal region [WBSCR]) or array comparative genomic hybridization. [1, 2, 3] The size of the deletion can vary; however, up to 95% of deletions are 1.55 Mb in size. [4, 5, 6, 7, 8]
Williams syndrome is not solely caused by elastin haploinsufficiency; the deletion involves a region that spans more than 28 genes and, hence, is considered a contiguous gene deletion syndrome. [4, 9, 10] The cardiovascular findings, part of the connective tissue pathology, and facial dysmorphology are attributed to the elastin gene haploinsufficiency. [11, 12]
Other genes within the region of the deletion are under investigation for their role in the cognitive profile of Williams syndrome, such as LIMK1, GTF1IRD1,GTF2IRD2, GTF2I, NCF1, STX1A, BAZ1B, CLIP2, and TFII-1. [10, 13, 14, 15, 16, 17, 18] LIMK1 and a number of other genes are felt to influence the cognitive profile of Williams syndrome, and other genes have been implicated in other features, such as hypercalcemia, facial features, glucose metabolism, and hypertension. However, genotype-phenotype correlations with genes other than elastin are not yet fully elucidated, and the sample size for studies involving individual genes has been small. [9, 19]
Point mutations or small intragenic deletions of ELN have been found in the autosomal dominant disorder familial supravalvular aortic stenosis (SVAS) without other characteristics of Williams syndrome. Point mutations and frameshift mutations in ELN have also been found in some cases of cutis laxa. [20, 21] Copy number variants (CNVs) in the 7q11.23 region have been found to be associated with autism in a study of over 4000 individuals who did not have Williams syndrome. 
Williams syndrome occurs in 1 per 7,500-20,000 births. Most cases are sporadic, however, in 25% of cases, a parent is found to have an inversion of chromosome 7 involving WBSCR, compared to 6% of the general population. 
Cardiovascular disease accounts for most cases of early mortality associated with Williams syndrome. Elastin arteriopathy is generalized; thus, virtually any artery may be affected.
Abnormalities involve local or diffuse stenosis of the medium-sized or large-sized arteries, most commonly in the ascending aorta above the aortic valves (ie, SVAS) or in the pulmonary arteries. Nonetheless, stenosis of the descending aorta, intracranial arteries, and renal arteries have been reported. [23, 24, 25] Overall, unexpected death is rare, but it is 25-fold to 100-fold higher than in age-matched control subjects.  Factors implicated in sudden death have included SVAS, severe pulmonary stenosis, and myocardial ischemia secondary to either coronary insufficiency or biventricular outflow tract obstruction with ventricular hypertrophy. Coronary insufficiency appears most likely because of stenosis that results from intimal fibrosis and muscular hypertrophy. Stroke occurring at younger than expected ages has been reported. [27, 28, 29, 30]
A study by Phomakay et al indicated that ventricular hypertrophy is a common finding on electrocardiograms (ECGs) in patients with Williams syndrome and that an association exists between the severity of right- and left-sided obstructive lesions and the presence of right or left ventricular hypertrophy, respectively, on electrocardiography. The study involved 187 patients, who underwent a total of 499 ECGs, with right ventricular hypertrophy being found on one or more ECGs in 57% (106) of patients and left ventricular hypertrophy being revealed on one or more ECGs in 39% (72) of patients. 
Deaths in patients with Williams syndrome have been reported after induction of anesthesia for minor surgical procedures, during cardiac catheterization and heart surgery, and with progressive heart failure and respiratory infection. [26, 32, 33] Sudden deaths with no apparent instigating event have also been reported, with apparent underlying myocardial injury.  Patients with a higher risk of sudden death may show signs of myocardial ischemia on electrocardiography (such as ST segment depression). Echocardiography, Holter monitoring, and careful evaluation should be considered before the use of anesthesia, sedation, or both or prior to an invasive procedure. Patients have also presented with syncope related to SVAS who died during diagnostic cardiac catheterization. Calcified valvular aortic stenosis has also been reported but not with sudden death. [34, 35]
A higher frequency of obesity, impaired glucose tolerance and diabetes mellitus have been found in adults with Williams syndrome compared to the general population.  Elevated thyroid stimulating hormone (TSH) levels have an increased prevalence in patients with William syndrome, are more common in children younger than 1 year, and are associated with thyroid hypoplasia.  Most of the findings are associated with subclinical hypothyroidism, but because TSH levels appear to normalize with age, there remains the possibility of thyroid hypoplasia that may not manifest with an elevated TSH level.
Various gastrointestinal problems are common, including feeding problems and colic, as well as reflux and chronic constipation.  Sigmoid diverticulitis in adults is reported at a higher frequency in the Williams syndrome population than in the general population. 
Williams syndrome is a multisystem condition with other potential consequences, including developmental delay, motor delay, hearing loss, severe dental disease, ocular problems, progressive joint contractures, nephrolithiasis, and bowel and bladder diverticula.
Williams syndrome is panethnic. The prevalence of particular features may vary among populations; for instance, peripheral pulmonary stenosis is more common than SVAS in the Hong Kong Chinese population,  and people living in Greece have a lower rate of cardiovascular anomalies. 
Clinical manifestations of Williams syndrome are evident from birth through adulthood. However, features that may be detected antenatally include the characteristic cardiovascular lesions. In addition, fetal ultrasonography of neonates with Williams syndrome has revealed multicystic dysplastic kidney in addition to the congenital heart lesions.  Associated findings on prenatal screening that have been reported include an increased fetal nuchal translucency and low maternal serum alpha fetoprotein (MSAFP); however, none of the prenatal findings has been proven to be a diagnostic marker of Williams syndrome.
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