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| DiseaseID |
HGD50 |
| Genetic
Disorder |
PRADER-WILLI SYNDROME
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| Gene
Name |
SNRPN gene |
| Description |
Prader-Willi syndrome is a rare genetic disorder characterized by decreased muscle tone, mental retardation and an intense desire to eat, which can lead to morbid obesity. Behavioral problems, such as temper tantrums or unusual food-seeking behavior, also are common features of this disorder. Prader-Willi syndrome is usually diagnosed by early childhood.
Initially, infants with Prader-Willi syndrome often have difficulty feeding but at about 1 year of age, children with this disorder develop voracious appetites and will gain weight quickly if their access to food is uncontrolled. Many of the complications from Prader-Willi syndrome are due to obesity.
There's no cure for Prader-Willi syndrome, but a team of specialists may work with you to manage your child's signs and symptoms and reduce the risk of developing complications.
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| Symptoms |
Some signs and symptoms of Prader-Willi syndrome become evident shortly after birth. These may include:
Poor muscle tone. A classical feature of babies with Prader-Willi syndrome is poor muscle tone (hypotonia). Hypotonic babies rest with their elbows and knees loosely extended instead of fixed and feel floppy or like "rag-dolls" when they're held.
Distinct facial features. Children with Prader-Willi syndrome are often born with almond-shaped eyes, narrowing at the temples, a turned-down mouth and a thin upper lip.
Failure to thrive. During the first year of life, children with Prader-Willi syndrome may have a poor sucking reflex due to decreased muscle tone. This makes feeding difficult, so they tend to gain weight slowly.
A weak cry and crossing of the eyes (strabismus) are other signs and symptoms of infants with Prader-Willi syndrome.
After the first year of life and into early childhood, children with Prader-Willi syndrome usually develop voracious appetites. They constantly crave food and tend to become morbidly obese if their food intake is left unchecked. Other signs and symptoms recognizable at this stage may include:
Underdeveloped sex organs. A condition called hypogonadism occurs when sex organs — the testes in men and the ovaries in women — produce little or no sex hormones. Children with Prader-Willi syndrome have underdeveloped sex organs.
Learning disabilities. Mild to moderate retardation is a common feature of children with Prader-Willi syndrome.
Delayed motor development. Toddlers with Prader-Willi syndrome often reach motor milestones, such as sitting at 12 months and walking at 24 months, later than other children.
Behavioral problems. In general, children with Prader-Willi syndrome are happy and pleasant to be around. However, these children may become very stubborn or throw temper tantrums, especially when denied food. They may also develop obsessive-compulsive disorders or unusual food-seeking behavior, such as eating garbage or frozen food.
Other signs and symptoms of young children with Prader-Willi syndrome may include:
Short stature
Small hands and feet
Nearsightedness (myopia)
Loss of skin pigmentation
Stretch marks (stria)
High pain tolerance
Skin picking
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| Causes |
Genes are segments of DNA that provide the "blueprints" for all of your characteristics — everything from hair color to the propensity to develop certain cancers. You receive your genes, which occur in pairs, from your parents. One copy comes from your mother, called the maternal copy, and the other copy comes from your father, the paternal copy.
Usually, both genes in each pair are "active" — meaning that information from both the maternal copy and the paternal copy of each gene pair are used by your cells. But in a small number of genes, only one copy of a gene pair is expressed — and the activity of each gene copy depends on whether it was passed from your mother or from your father. This is called imprinting.
Such is the case with Prader-Willi syndrome. A portion of the paternal gene copy on a region of chromosome 15 is either inactive or defective. Since the maternal gene copy in this pair is usually inactive, no active or normal gene copy remains — and Prader-Willi syndrome results.
Prader-Willi syndrome affects a portion of your child's brain called the hypothalamus. Among its many functions, the hypothalamus controls hunger and thirst and releases hormones that prompt the release of other substances responsible for growth and sexual development. A malfunctioning hypothalamus — caused by the defect on chromosome 15 — interferes with each of these processes, resulting in uncontrollable hunger, stunted growth and sexual underdevelopment in children with Prader-Willi syndrome |
| Diagnosis |
Your doctor may suspect that your child has Prader-Willi syndrome at birth if your child has the characteristic facial features — almond-shaped eyes, a misalignment of the eyes (strabismus), narrowing at the temples, a turned-down mouth and a thin upper lip — and other signs of the disorder, such as floppiness (hypotonia) and underdeveloped reproductive organs.
To confirm the suspected diagnosis, your doctor obtains a blood sample from your child to perform genetic testing. A karyotype is a genetic testing technique in which your child's chromosomes are stained and arranged by pairs in numerical order on film. By examining each chromosome pair, your doctor can determine whether the chromosomes are abnormally shaped or missing. A specialized genetic test called a methylation analysis is very sensitive and can detect nearly every case of Prader-Willi syndrome.
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| Treatment |
A team of health professionals will likely work with you to manage your child's condition. Depending on your child's signs and symptoms, treatment for Prader-Willi syndrome may involve the following:
Encouraging feeding during infancy. Many infants with Prader-Willi syndrome have difficulty feeding due to decreased muscle tone. Your pediatrician may recommend a high-calorie formula to help your baby gain weight and will likely monitor your child's development as he or she begins to grow.
Replenishing hormone deficiencies. Human growth hormone stimulates bone growth and muscle and organ development. Some studies have suggested that growth hormone treatment in children with Prader-Willi syndrome helps increase growth and decrease body fat, but the long-term effects of growth hormone treatment aren't known. A doctor who treats hormonal disorders (endocrinologist) can help determine whether your child would benefit from growth hormone treatment.
Your endocrinologist may also suggest that your child take hormone replacement therapy (testosterone for males or estrogen and progesterone for females) to replenish low levels of sex hormones. Hormone replacement therapy can help decrease your child's risk of developing thinning of the bones (osteoporosis).
Following a low-calorie diet. A nutritionist may help you develop a healthy, reduced-calorie diet to keep your child's weight under control. However, to ensure proper nerve cell development in the first few years of life, a low-calorie diet isn't recommended for children under the age of 3.
Improving motor skills. Physical therapists may guide your child through exercises to help him or her maintain a healthy weight, develop motor skills and strengthen back muscles to help prevent an abnormal curving of the spine (scoliosis).
Correcting vision problems. Some children with Prader-Willi syndrome have crossed eyes (strabismus). A doctor who specializes in disorders of the eyes (ophthalmologist) may prescribe glasses, eye exercises or a patch that's placed over your child's normal eye to help improve strabismus.
Treating sleep apnea. Sleep apnea, or pauses in breathing during sleep, can be serious because it can cause high blood pressure and rarely, sudden death. A doctor who specializes in lung problems (pulmonologist) may recommend surgery, an oral device to keep your child's throat open or another therapy.
Addressing psychological disorders. A mental health professional, such as a psychologist or a psychiatrist, may help address any psychological problems your child may have, such as obsessive-compulsive tendencies or mood disorders. Some children may need medication to control behavioral problems. |
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