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PURPOSE OF REVIEW: Williams syndrome is a multisystem disorder caused by a microdeletion on chromosome 7q. Throughout infancy, childhood, and adulthood, abnormalities in body composition and in multiple endocrine axes may arise for individuals with Williams syndrome. This review describes the current literature regarding growth, body composition, and endocrine issues in Williams syndrome with recommendations for surveillance and management by the endocrinologist, geneticist, or primary care physician. RECENT FINDINGS: In addition to known abnormalities in stature, calcium metabolism, and thyroid function, individuals with Williams syndrome are increasingly recognized to have low bone mineral density, increased body fat, and decreased muscle mass. Furthermore, recent literature identifies a high prevalence of diabetes and obesity starting in adolescence, and, less commonly, a lipedema phenotype in both male and female individuals. Understanding of the mechanisms by which haploinsufficiency of genes in the Williams syndrome-deleted region contributes to the multisystem phenotype of Williams syndrome continues to evolve. SUMMARY: Multiple abnormalities in growth, body composition, and endocrine axes may manifest in individuals with Williams syndrome. Individuals with Williams syndrome should have routine surveillance for these issues in either the primary care setting or by an endocrinologist or geneticist.
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Williams syndrome (WS) is a relatively rare microdeletion disorder that occurs in as many as 1:7,500 individuals. WS arises due to the mispairing of low-copy DNA repetitive elements at meiosis. The deletion size is similar across most individuals with WS and leads to the loss of one copy of 25–27 genes on chromosome 7q11.23. The resulting unique disorder affects multiple systems, with cardinal features including but not limited to cardiovascular disease (characteristically stenosis of the great arteries and most notably supravalvar aortic stenosis), a distinctive craniofacial appearance, and a specific cognitive and behavioural profile that includes intellectual disability and hypersociability. Genotype–phenotype evidence is strongest for ELN, the gene encoding elastin, which is responsible for the vascular and connective tissue features of WS, and for the transcription factor genes GTF2I and GTF2IRD1, which are known to affect intellectual ability, social functioning and anxiety. Mounting evidence also ascribes phenotypic consequences to the deletion of BAZ1B, LIMK1, STX1A and MLXIPL, but more work is needed to understand the mechanism by which these deletions contribute to clinical outcomes. The age of diagnosis has fallen in regions of the world where technological advances, such as chromosomal microarray, enable clinicians to make the diagnosis of WS without formally suspecting it, allowing earlier intervention by medical and developmental specialists. Phenotypic variability is considerable for all cardinal features of WS but the specific sources of this variability remain unknown. Further investigation to identify the factors responsible for these differences may lead to mechanism-based rather than symptom-based therapies and should therefore be a high research priority.
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OBJECTIVE: We assessed body composition, bone mineral density (BMD), glucose and lipids in Williams syndrome (WS), a rare microdeletion disorder. DESIGN: Individuals with WS had outpatient assessment at Massachusetts General Hospital. Controls were selected from the National Health and Nutrition Examination Survey (NHANES 2005-2006). PATIENTS: A total of 22 individuals with WS, each matched by age, sex and race to four NHANES controls. MEASUREMENTS: Blood sampling, oral glucose tolerance test, dual-energy X-ray absorptiometry scan. RESULTS: WS and control groups were 59% female and 29 ± 8 years old. Compared to controls, individuals with WS were shorter but had similar body weight, with more fat and less lean mass. Per cent body fat was higher in WS even after adjusting for BMI (+2.1% [95% CI 0.4, 3.9%]). Four WS patients had abnormal lower extremity fat accumulation resembling lipedema. HbA1c (+0.5% [0.2, 0.7]) and 2-hour glucose (+68 mg/dL [44, 93]) were higher in WS vs controls, differences which persisted after adjusting for BMI. Fasting glucose was comparable between groups. LDL (-18 mg/dL [-35, -2]) and triglycerides (-45 mg/dL [-87, -2]) were significantly lower in WS. Whole-body BMD was significantly lower (-0.15 g/cm(2) [-0.20, -0.11]) in WS, and this remained true controlling for height (-0.06 g/cm(2) [-0.11, -0.02]). Vitamin D was <30 ng/mL in 81% of those with WS. CONCLUSIONS: On average, adults with WS have increased fat, decreased lean mass, impaired glucose homeostasis and reduced BMD. Clinical efforts to build muscle and bone mass, and to ensure vitamin D sufficiency, are warranted. Genotype-phenotype research efforts are also warranted.
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