A newborn boy has severe generalized hypotonia, weak cry, poor feeding requiring nasogastric tube feeds, and undescended testes. By age 4 years he has developed insatiable appetite and marked obesity. Which diagnostic test will best confirm the suspected condition?

• A DNA methylation analysis of the 15q11-q13 region ✓
• B Karyotype with high-resolution banding
• C Serum creatine kinase estimation
• D Urine organic acid profile by gas chromatography

Explanation

The combination of neonatal hypotonia with feeding difficulty, later hyperphagia and obesity, and cryptorchidism indicates Prader-Willi syndrome, caused by loss of expression of paternally inherited genes at 15q11-q13. DNA methylation analysis detects absence of the paternal methylation pattern and confirms over 99 percent of cases regardless of the underlying mechanism. Standard karyotype misses most deletions, creatine kinase is normal because the hypotonia is central, and organic acids are normal.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.