Prader-Willi syndrome (PWS) is a rare genetic disorder with genetic aberrations on chromosome number 15 out of all 23 pairs of chromosomes. The random errors during reproduction and gamete formation in parents and transfer to their offspring are behind the etiology of PWS. PWS can be clinically detected early in patients with obesity and increased eating habits. Mostly, this genetic imprinting disorder with the deficit in paternal expression of the 15q11-q13 region is found in about 60% of the patients.

PWS is named after Swiss endocrinologists Andrea Prader, Alexis Labhart, and Heinrich Willi, who were the first to describe the clinical characteristics in 1956. Their observations were further developed in the late 1960s and additional characteristics were identified that facilitated differential diagnosis of the disease. The clinical manifestations of the disease include multiple implications on metabolic, endocrine, and neurological systems, along with behavioral and intellectual disabilities.

Symptoms

PWS can cause a wide range of symptoms, and affect a person's physical, psychological, and behavioral development. In infancy, PWS is characterized by weak muscle tone (hypotonia), feeding difficulties, poor growth, and delayed development. In later infancy or early childhood, affected children develop an extreme appetite, which leads to overeating and obesity.

Other signs and symptoms of PWS may include:

• Mild to moderate intellectual disability

• Sleep abnormalities

• Unusually fair skin

• Underdeveloped genitals

• Delayed or incomplete puberty

• Short stature

• Strabismus

• Scoliosis

• Small hands and feet

• Distinctive facial features such as a narrow forehead, almond-shaped eyes, and a triangular mouth

• Behavioral problems are common and often include temper tantrums, stubbornness, and obsessive-compulsive tendencies.

Diagnosis

Consensus diagnostic criteria for PWS were developed in 1993 and confirmed to be accurate and continue to be useful to clinicians. However, the confirmation of the diagnosis needs molecular genetic testing, but it was not widely accessible when the criteria was  developed. PWS should be suspected in individuals with the specific clinical findings (classified by age), which should be rapid diagnostic testing, as listed below:

• Birth to age 2 years: Hypotonia with a poor suck (neonatal period) and feeding problems.

• Ages 2-6 years: History of congenital central hypotonia, poor suck, and global developmental delay.

• Ages 6-12 years: History of hypotonia with poor suck, global developmental delay, food foraging with hyperphagia, and central obesity. 

• Ages 13 years to adulthood: Cognitive impairment, mild intellectual disability, hyperphagia with central obesity, behavioral problems (e.g., temper tantrums, self-injury), and hypothalamic hypogonadism.

Genetic testing is called DNA methylation testing. This testing can detect abnormal, parent-specific imprinting on the region of chromosome 15 that is responsible for PWS. It determines whether the region is maternally inherited only (i.e., the paternally contributed region is absent) and confirms a diagnosis in more than 99% of affected people. DNA methylation testing is especially important in people who have non-classic features or are too young to show enough features to make the diagnosis based on signs and symptoms alone.

Certain other tests are required to be done to assess related complications. They are:

• Thyroid function tests to assess hypothyroidism, especially before initiating any growth hormone treatment; 

• Liver function tests and serum insulin-like growth factor-1 (IGF-1) to evaluate growth hormone deficiency;

• Fasting glucose levels and oral glucose tolerance test to investigate diabetes;

• Polysomnography (sleep study) to diagnose any sleep disorders; and

• Dual X-ray absorptiometry (DXA scan) to assess bone mineralization and composition.

Treatment

Recombinant Human Growth Hormone (rhGH) is recommended in patients with PWS as an early intervention at the time of diagnosis (from 3 to 6 months old) as it can improve body composition and physical strength, as well as motor and mental development.

Human chorionic gonadotropic hormone (hCG) may be used in male PWS patients with cryptorchidism to help lower the testicle position; however, most of them still need orchiopexy (a surgery to move an undescended or cryptorchid testicle into the scrotum and permanently fix it there).

FDA has approved testosterone as an intramuscular injection as a treatment for hypogonadism and induction of puberty in males with PWS (in late childhood and early adulthood), as well as for the prevention of osteoporosis. Similarly for the treatment of hypogonadism and induction of puberty in females with PWS as well as for the prevention of osteoporosis low-dose transdermal patches of estrogen are applied to begin at around age 12 years (for usually two years or until the time of menarche).  Micronized progestin may also be used in combination with estrogen for the treatment of hypogonadism in females with PWS as it helps to prevent endometrial hyperplasia, usually 2 years after the initiation of estrogen treatment.

Psychotropic medications may be prescribed to target situational behavioral disturbances and/or to treat symptoms of psychiatric disorder in individuals with PWS. A common practice in PWS is to begin the medication at a low dose and adjust upward with caution when indicated by the pediatrician or physician. Stimulant medications (like methylphenidate, dexmethylphenidate, dextroamphetamine, lisdexamfetamine, and mixed amphetamine salts) may be prescribed for the treatment of symptoms of Attention Deficit Hyperactive Disorder (ADHD), excessive daytime sleepiness, or narcolepsy. Non-stimulant medications that may be used for the treatment of symptoms of ADHD, disruptive behavior associated with hyperarousal and anxiety include atomoxetine, guanfacine, and clonidine.

Other non-stimulant medications for the treatment of excessive daytime sleepiness and narcolepsy include modafinil and armodafinil. Selective serotonin reuptake inhibitors (SSRIs) (like fluoxetine, paroxetine, sertraline, fluvoxamine, citalopram, and escitalopram) are usually prescribed for the treatment of anxiety, depression, obsessive/compulsive tendencies, and cognitive rigidity in PWS. Also, selective serotonin and norepinephrine reuptake inhibitors (SSNRIs) (like Venlafaxine HCl, Desvenlafaxine HCl, and Duloxetine) are used for the treatment of anxiety and refractory depression in adolescents with PWS. However, in the case of both SSRIs and SSNRIs FDA reports increased awareness of the risk of suicidal ideation and behavior. Antidepressants (like Bupropion HCl, Trazadone, Doxepin), antianxiety agents (like Benzodiazepines, Lorazepam, Clonazepam), antipsychotics (like Risperidone, Aripiprazole, Ziprasidone, Olanzapine), and mood stabilizers (like Lithium, Carbamazepine, Topiramate, etc.) may be prescribed for managing depression, anxiety attacks, psychosis, bipolar disorder, and picking behaviors in PWS. Supplements like calcium and vitamin D (for the prevention of osteopenia/ osteoporosis), omega-3 fish oils (for mood and behavioral stability; prevention of seasonal affective disorder), and N-acetyl Cysteine (for treating skin picking) also help in preventing various disorders/complications associated with PWS.