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Williams syndrome


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16/05/2016

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Williams syndrome, also known as Williams-Beuren syndrome, is a rare genetic disorder characterized by growth delays before and after birth (prenatal and postnatal growth retardation), short stature, a varying degree of mental deficiency, and distinctive facial features that typically become more pronounced with age. Such characteristic facial features may include a round face, full cheeks, thick lips, a large mouth that is usually held open, and a broad nasal bridge with nostrils that flare forward (anteverted nares). Affected individuals may also have unusually short eyelid folds (palpebral fissures), flared eyebrows, a small lower jaw (mandible), and prominent ears. Dental abnormalities may also occur including abnormally small, underdeveloped teeth (hypodontia) with small, slender roots. Williams syndrome may also be associated with heart (cardiac) defects, abnormally increased levels of calcium in the blood during infancy (infantile hypercalcemia), musculoskeletal defects, and/or other abnormalities. Cardiac defects may include obstruction of proper blood flow from the lower right chamber (ventricle) of the heart to the lungs (pulmonary stenosis) or abnormal narrowing above the valve in the heart between the left ventricle and the main artery of the body (supravalvular aortic stenosis). Musculoskeletal abnormalities associated with Williams syndrome may include depression of the breastbone (pectus excavatum), abnormal side-to-side or front-to-back curvature of the spine (scoliosis or kyphosis), or an awkward gait. In addition, most affected individuals have mild to moderate mental retardation; poor visual-motor integration skills; a friendly, outgoing, talkative manner of speech; a short attention span; and are easily distracted. In most individuals with Williams syndrome, the disorder appears to occur spontaneously for unknown reasons (sporadically). However, familial cases have also been reported. Sporadic and familial cases are thought to result from deletion of genetic material from adjacent genes (contiguous genes) within a specific region of chromosome 7 (7q11.23). Signs & Symptoms Williams syndrome is characterized by a wide spectrum of symptoms and physical features that vary greatly in range and severity, even among affected family members. Individuals with Williams syndrome will not have all the symptoms listed below. Some affected individuals do not have heart (cardiac) abnormalities; others may not have elevated levels of calcium in the body (hypercalcemia). In addition, the severity of these symptoms often varies greatly from case to case. Some children with Williams syndrome may have a low birth weight, feed poorly, and fail to gain weight and grow at the expected rate (failure to thrive). Symptoms such as vomiting, gagging, diarrhea, and constipation are common during infancy. Some affected infants may have elevated levels of calcium in their blood (hypercalcemia), leading to loss of appetite, irritability, confusion, weakness, easy fatigability, and/or abdominal and muscle pain. Calcium levels usually return to normal around the age of 12 months. However, in some cases, hypercalcemia may last into adulthood. Linear growth may be delayed during the first four years of life. However, growth spurts usually occur between the age of five and 10 years. Most people with Williams syndrome are less than average height during their adult years. Newborns with Williams syndrome have characteristic “elfin-like” facial features including an unusually small head (microcephaly), full cheeks, an abnormally broad forehead, puffiness around the eyes and lips, a depressed nasal bridge, broad nose, and/or an unusually wide and prominent open mouth. Additional features may include a vertical skin fold on the inner corners of the eyes (epicanthal folds), a small pointed chin, prominent ears, and/or an unusually long vertical groove in the center of the upper lip (philtrum). Some infants with Williams Syndrome may have dental abnormalities including malformed teeth (i.e., hypoplastic enamel), small teeth (microdontia), and upper and lower teeth that do not meet properly (malocclusion). A star-like (stellate) pattern in the iris of the eye may be apparent in about 50 percent of children with this disorder. It is most pronounced in those infants with blue or green eyes. This pattern may be harder to see in those children with darker eyes or it may not be present. Affected infants may also experience inward deviation of the eyes (esotropia) and farsightedness (hyperopia). Children with Williams syndrome are extremely sensitive to sound and may overreact to unusually loud or high-pitched sounds (hyperacusis). Chronic middle ear infections (otitis media) are often present. Motor development, (e.g., sitting and walking) and/or gross and fine motor skills (e.g., picking up an object) may be delayed. The development of secondary sexual characteristics (e.g., pubic hair and underarm hair) may occur prematurely (precocious puberty) in children with this disorder. Breast development and menstruation may occur earlier than expected in females with Williams syndrome. Individuals with this disorder may also have an unusually hoarse voice. Congenital heart defects (CHD) occur in approximately 75 percent of children with Williams syndrome. The most frequent defect is supravalvar aortic stenosis, a condition characterized by the narrowing of the aorta above the aortic valve. The aorta is the main artery of the vascular system. Blood passes from the left ventricle of the heart, through the aortic valve, and into the aorta. In supravalvar aortic stenosis, the area above the aortic valve becomes unusually narrow. Symptoms may include fatigue, pain in the chest, dizziness, unusual heart sounds (murmurs) and/or temporary loss of consciousness (syncope). The amount of narrowing of the aorta may vary among affected individuals. Additional congenital heart defects associated with Williams syndrome may include pulmonary artery stenosis, and/or septal defects. (For more information on these heart defects, see the Related Disorders section of this report.) Abnormally high blood pressure (hypertension) is also common in adults with this disorder. Children with Williams syndrome typically have a personality that is friendly, outgoing, and/or talkative. The appropriate use of language and vocabulary range may be unusually enhanced in some children with this disorder. Mild to moderate mental retardation may occur. However, some children are of average intelligence with severe learning disabilities. Hyperactivity and attention deficit disorder are also common, although most affected individuals have good long-term memory. Some affected individuals may have visual difficulties; they may tend to view a picture in parts as opposed to seeing it as a whole. Older children and adults with Williams syndrome may develop progressive joint problems that limit their range of motion. Skeletal abnormalities such as backward (lordosis), front-to-back (kyphosis), and side-to-side (scoliosis) curvature of the spine may also be present. Some affected individuals may have a sunken breastbone (pectus excavatum) and inward turning of the great toe toward the other toes (hallux valgus). Skeletal and joint abnormalities may result in an abnormal manner of walking (awkward gait). Skeletal abnormalities may become worse as affected individuals age. Additional abnormalities may occur in some individuals with Williams syndrome including kidney (renal) abnormalities, chronic urinary tract infections, an underdeveloped (hypoplastic) thyroid gland, and umbilical or inguinal hernias. Causes Most cases of Williams syndrome appear to occur spontaneously (sporadically) for unknown reasons. However, some familial cases of the disorder have also been reported. Ongoing research indicates that sporadic and familial Williams syndrome result from deletions of genetic material from adjacent genes (contiguous genes) located on the long arm (q) of chromosome 7 (7q11.23). This chromosomal region has been designated “Williams-Beuren Syndrome chromosome region 1” (WBSCR1). Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Pairs of human chromosomes are numbered from 1 through 22, and an additional 23rd pair of sex chromosomes which include one X and one Y chromosome in males and two X chromosomes in females. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome 11p13” refers to band 13 on the short arm of chromosome 11. The numbered bands specify the location of the thousands of genes that are present on each chromosome. According to investigators, 28 genes within the 7q11.23 chromosomal region may play a causative role in Williams syndrome including those known as the ELN (elastin) gene, the LIMK1 (or LIM kinase-1) gene, and the RFC2 (replication factor C, subunit 2) gene. The LIMK1 gene is believed to be involved with visual-spatial problems associated with Williams syndrome. In familial cases, Williams syndrome is inherited as an autosomal dominant trait. Genetic diseases are determined by two genes, one received from the father and one from the mother. Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy regardless of the sex of the resulting child. Hypercalcemia, which is associated with some cases of Williams syndrome, may occur because of an abnormal sensitivity to vitamin D. Affected Populations Williams syndrome is a rare disorder that affects males and females in equal numbers and infants of any race may be affected. The prevalence of this disorder is approximately one in 10,000-20,000 births in the United States. Related Disorders Symptoms of the following disorders can be similar to those of Williams Syndrome. Comparisons may be useful for a differential diagnosis: Noonan syndrome is a rare genetic disorder that is typically evident at birth (congenital). The disorder may be characterized by a wide spectrum of symptoms and physical features that vary greatly in range and severity. In many affected individuals, associated abnormalities include a distinctive facial appearance; a broad or webbed neck; a low hairline in the back of the head; and short stature. Characteristic abnormalities of the head and facial (craniofacial) area may include widely set eyes (ocular hypertelorism); vertical skin folds that may cover the eyes’ inner corners (epicanthal folds); drooping of the upper eyelids (ptosis); a small jaw (micrognathia); a low nasal bridge; and low-set, prominent, abnormally rotated ears (pinnae). Distinctive skeletal malformations are also typically present, such as abnormalities of the breastbone (sternum), curvature of the spine (kyphosis and/or scoliosis), and outward deviation of the elbows (cubitus valgus). Many infants with Noonan syndrome also have heart (cardiac) defects, such as obstruction of proper blood flow from the lower right chamber of the heart to the lungs (pulmonary valvular stenosis). Additional abnormalities may include malformations of certain blood and lymph vessels, blood clotting and platelet deficiencies, mild mental retardation, failure of the testes to descend into the scrotum (cryptorchidism) by the first year of life in affected males, and/or other symptoms and findings. (For more information on this disorder, choose “Noonan” as your search term in the Rare Disease Database.) Idiopathic infantile hypercalcemia is characterized by the elevation of blood calcium levels in a newborn for which there is no apparent cause (idiopathic). Symptoms may include loss of appetite (anorexia), irritability, confusion, weakness, easy fatigability, and/or abdominal and muscle pain. Some studies in the medical literature question whether idiopathic infantile hypercalcemia is a separate disorder from Williams Syndrome or if it is a variant of the same disease. Infants with this form of the disease do not have the characteristic facial features or heart defects that are associated with Williams Syndrome. Leprechaunism is a rare progressive inherited endocrine disorder characterized by overgrowth (hyperplasia) of the pancreas, inability to properly utilize insulin (insulin resistance), and excessive amounts of estrogen. Growth retardation begins during fetal development. Symptoms of Leprechaunism may include short arms and legs, large hands, an elfin-like face, sunken cheeks, a pointed chin, a flat broad nose, low-set ears, and widely spaced eyes. Children with Leprechaunism usually have low levels of circulating glucose (hypoglycemia) and elevated levels of insulin (hyperinsulinemia). People with this disorder are not able to use the insulin effectively. (For more information on this disorder, choose “Leprechaunism” as your search term in the Rare Disease Database.) The following disorders may be associated with Williams Syndrome as secondary characteristics. They are not necessary for a differential diagnosis: Pulmonary artery stenosis is a rare congenital heart defect characterized by unusual narrowing of the vessel that carries blood from the right ventricle of the heart to the lungs (pulmonary artery). This defect usually occurs in association with other heart defects, such as septal defects and/or supravalvar aortic stenosis. Symptoms may include unusual heart sounds (murmurs), difficulty breathing, chest pain, and, in severe cases, congestive heart failure. Ventricular septal defects are heart defects that are present at birth (congenital) and can occur in any portion of the ventricular septum. The size and location of the defect determines the severity of the symptoms. Small ventricular septal defects can close on their own or become less significant over time. Moderately-sized defects can cause congestive heart failure resulting in an abnormally rapid rate of breathing (tachypnea), wheezing, an unusually fast heartbeat (tachycardia), enlargement of the liver, and/or failure to thrive. Large ventricular defects can cause life-threatening complications during infancy. (For more information on this disorder, choose “Ventricular Septal Defects” as your search term in the Rare Disease Database.) Attention Deficit Hyperactivity disorder is a behavioral disorder of childhood characterized by a short attention span, excessive impulsiveness, and inappropriate hyperactivity. This disorder is usually observed before the child reaches the age of 4 years. In some cases, it may not be diagnosed until the child starts school. Symptoms may vary depending on environmental factors and typically worsen when sustained attention is required. Symptoms usually improve with frequent reinforcement in a structured setting without distractions. (For more information on this disorder, choose “Attention Deficit Hyperactivity” as your search term in the Rare Disease Database.) Diagnosis The diagnosis of Williams syndrome may be confirmed by a thorough clinical evaluation that includes a detailed patient history and specialized blood tests that may detect elevated levels of calcium in the blood. Another test, known as fluorescent in situ hybridization [FISH], may be used to determine whether a deletion of one elastin gene on chromosome 7 is present. This deletion is believed to occur in the majority of individuals with Williams Syndrome. Standard Therapies Treatment Infants with Williams syndrome who have elevated levels of calcium in their blood may be placed on a diet that restricts the intake of vitamin D. Calcium intake may also be restricted. For those children with severe hypercalcemia, treatment with a corticosteroid drug (e.g., prednisone) may be considered on a temporary basis. After the age of about 12 months, calcium levels typically return to normal, even in untreated infants. It is recommended that children with Williams Syndrome also be evaluated by a physician who specializes in endocrine disorders (endocrinologist). Affected children, who have symptoms related to heart defects, should receive a comprehensive evaluation at a hospital that is familiar with these rare congenital heart conditions. Specialized tests may be performed to determine the severity and exact location of congenital heart defects (i.e., EKG, echocardiogram, or cardiac catheterization). Some children with Williams Syndrome who have severe heart defects may require surgical treatment to repair the defect. Centers for developmentally disabled children and special education services in schools may be beneficial for children with Williams syndrome to reach their personal potential. A supportive team approach may also be helpful including speech and language therapy, occupational and physical therapy, social services, and/or vocational training. Music therapy has been advocated, thought not proven, as providing enhanced learning and relief from anxiety in individuals with Williams syndrome.

Etiquetas:   Genética   ·   Psiquiatría

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