Overview: Prader-Willi syndrome (PWS) is a disorder caused by a deletion or disruption of genes in the proximal arm of chromosome 15 or by maternal disomy in the proximal arm of chromosome 15.
|Patient with Prader Willi Syndrome|
Phenotype/Characteristics and Diagnosis:
A diagnostic criteria for Prader-Willi syndrome was made by Holm et al. Based on these guidelines, the diagnosis of Prader-Willi syndrome is highly likely in children younger than 3 years with 5 points (3 from major criteria) or in those older than 3 years with 8 points (4 from major criteria).
· Major criteria (1 point each)
o CNS - Infantile central hypotonia
o GI - Infantile feeding problems and/or failure to thrive
o Nutrition - Rapid weight gain in children aged 1-6 years
o Craniofacial - Characteristic facial features such as narrow bifrontal diameter, almond-shaped palpebral fissures, narrow nasal bridge, and down-turned mouth
o Endocrine - Hypogonadism
o Developmental - Developmental delay and/or mental retardation
· Minor criteria (one half point each)
o Neurologic - Decreased fetal movement and/or infantile lethargy
o Pulmonary - Sleep disturbance and/or sleep apnea
o Endocrine - Short stature for predicted height by mid adolescence
o Dermatologic - Hypopigmentation
o Orthopedic - Small hands and feet
o Orthopedic - Narrow hands with straight ulnar border
o Ophthalmologic – Esotropia and/or myopia
o Dental - Thick viscous saliva
o Otolaryngology - Speech articulation defects
o Psychiatric - Skin picking (Some patients with Prader-Willi syndrome have become anemic from chronic rectal bleeding secondary to skin picking.)
· Supportive criteria (no points)
o Neurology - High pain threshold and normal neuromuscular evaluation for hypotonia
o Gastroenterology - Decreased vomiting
o Endocrinology - Ineffective thermoregulation, early adrenarche, and/or osteoporosis, adrenal insufficiency
o Orthopedics – Scoliosis or kyphosis
o Developmental - Jigsaw puzzle proficiency
Frequency: Prader-Willi syndrome affects an estimated 1 in 10,000 to 30,000 people worldwide. Differences in prevalence rates between sexes have not been reported
Genetic testing is employed for accurate diagnosis of the condition.
· Genetic testing for Prader-Willi syndrome (PWS) includes chromosomal analysis and assessment for methylation patterns in the Prader-Willi syndrome region.
· Methylation patterns can be determined with Southern blot hybridization or polymerase chain reaction (PCR) using DNA primers that can detect methylated cytosine.
· Analysis for underlying uniparental disomy requires samples from both parents and the child with Prader-Willi syndrome.
· Fluorescent in situ hybridization (FISH) can be used to confirm prenatal diagnosis when a deletion in the 15q region is suspected after chorionic villus sampling or amniocentesis.
· Prader-Willi syndrome is due to the loss of the paternal copy of chromosome 15q11.2-13.
· Most cases of Prader-Willi syndrome are sporadic. More than 70% of patients have a deletion of the paternal copy; approximately 25% of patients with Prader-Willi syndrome have maternal uniparental disomy in chromosome 15. The remainder of patients with this disorder have a translocation or other structural alteration in chromosome 15.
· Most manifestations of Prader-Willi syndrome are attributable to hypothalamic dysfunction.
Patients with Prader-Willi syndrome (PWS) frequently require medical care for the following:
· Initial management of hypotonia or poor feeding
· Evaluation for hypogonadism or hypopituitarism
· Management of obesity
· Monitoring for scoliosis
· Therapy for behavioral issues
Patients with Prader-Willi syndrome may require surgical care for treatment of complications of obesity, treatment of cryptorchidism, and scoliosis intervention.
Tonsillectomy, adenoidectomy, or tracheostomy placement may be required in patients with obstructive sleep apnea.
Biliopancreatic diversion and gastric bypass surgery have been ineffective for long-term weight reduction. Patients with Prader-Willi syndrome have hyperphagia and require restricted access to foods to minimize weight gain. Binge-eating episodes may predispose patients to development of food poisoning and acute gastric dilation. Caregivers of patients with Prader-Willi syndrome should be instructed in the Heimlich maneuver.
Growth hormone therapy in patients with growth hormone deficiency improves lean body mass and corrects osteopenia.
Patients with Prader-Willi syndrome (PWS) may require inpatient evaluation and treatment for hypotonia and poor feeding during infancy.
Individuals with Prader-Willi syndrome and other medical issues, including scoliosis and complications of obesity or pickwickian syndrome, may require inpatient therapy.
Patients with severe behavioral problems may merit admission to a facility staffed with individuals with long-term experience with Prader-Willi syndrome.
A.D.A.M.Health Solutions, Ebix, Inc. (2012)
Genetics Home Reference (2011). Prader Willi Syndrome. Genetics Home reference. Retrieved March 12, 2013 from the URL: http://ghr.nlm.nih.gov/condition/prader-willi-syndrome
Scheimann, A. (2012).