Severe Single-Gene Disorders & Multi-System Deletions

Prader-Willi Syndrome (PWS)

15q11-q13 Paternal Chromosomal Deletion Syndrome

Primary risk age: Neonates through adulthood (recognized at birth due to hypotonia)

Urgency: Severe
Typical age: Neonates through adulthood (recognized at birth due to hypotonia)
Body system: Genetic & Chromosomal

Typical course: This is a lifelong genetic chromosomal disorder; management is continuous and daily.

Reviewed against AAP · CDC · WHO · NHS guidance Last reviewed 2026-06-13

1. Summary & Pathophysiology

15q11-q13 Paternal Chromosomal Deletion Syndrome

Pathophysiology (Development Path)

Loss of these active genes disrupts hypothalamic development, leading to hypothalamic dysfunction. This causes growth hormone deficiency, hypogonadism, and a severe dysregulation of satiety mechanisms (hyperphagia).

Primary Causes & Etiology

Loss of active paternal genes in the 15q11-q13 region on chromosome 15 (due to deletion, maternal uniparental disomy, or imprinting defect).

2. Symptom Continuum

Early Onset Signs
Severe neonatal hypotonia ("floppy baby"), weak sucking reflex requiring tube feeding, and developmental delays.
Progressive Phase
Onset of hyperphagia (insatiable, obsessive hunger) between ages 2 and 8, rapid weight gain, short stature, and small hands/feet.
Severe Indicators
Extreme morbid obesity leading to cardiovascular strain, sleep apnea, type 2 diabetes, hypogonadism (undeveloped sex organs), and behavioral outbursts.

3. Clinical Verification

DNA methylation testing showing maternal-only imprint in the 15q11-q13 region. Confirmed with FISH or chromosomal microarray.

4. Care & Elements Plan

Primary Care Treatment Plan

Initiate recombinant human growth hormone therapy in infancy to improve muscle tone and growth. Enforce strict restriction of access to food. Address behavioral outbursts.

Home Support Elements

Lock kitchen cabinets and refrigerators. Enforce a strict low-calorie, portion-controlled diet. Encourage daily physical activity and maintain highly predictable routines.

Generic Active Ingredients (No Brands)

Somatropin (recombinant human growth hormone active ingredient to support growth and lean muscle mass).

Lists active elements only. Never administer self-designed therapies.

5. Doctor Critical Lines

Critical Thresholds: When to See a Doctor

Consult a geneticist immediately if a newborn exhibits severe hypotonia, or if a toddler shows sudden, uncontrollable food-seeking behaviors and rapid weight gain.

6. Vaccine & Prevention

Routine Prophylaxis (Prevention)

No primary prevention exists, as the chromosomal abnormality is a random de novo imprinting or deletion event.

Immunization Context

Follow standard pediatric immunization schedules.

7. Timelines & Outlook

Active Timeline

This is a lifelong genetic chromosomal disorder; management is continuous and daily.

Expected Prognosis

Good if obesity is successfully prevented. Individuals require lifelong supervision regarding food access and daily living.

Potential Untreated Complications

Morbid obesity, type 2 diabetes, sleep apnea, cor pulmonale, scoliosis, and severe behavioral problems.

Severe

Cystic Fibrosis (CF)

Autosomal Recessive Multi-System Exocrine Disorder

Infancy through Adulthood (Screened at birth; symptoms develop in infancy)

Moderate

Williams Syndrome

Autosomal Dominant Microdeletion Syndrome

Apparent in infancy and early childhood (Lifelong condition)