Differentials
Spinal muscular atrophy
SIGNS / SYMPTOMS
Worsening hypotonia with age, feeding difficulties that persist beyond infancy, and respiratory insufficiency.[42]
INVESTIGATIONS
Genetic testing reveals mutations or deletions of the SMN1 gene.
Angelman syndrome
SIGNS / SYMPTOMS
Signs and symptoms are similar to Prader-Willi syndrome in infancy (i.e., hypotonia, poor feeding in the neonatal period, small hands and feet, hypopigmentation), but there is no hypogonadism. Patients with Angelman syndrome may also have ataxia, lack of speech, and microcephaly.
INVESTIGATIONS
Genetic testing reveals 15q11-12 deletion.
Temple syndrome
SIGNS / SYMPTOMS
Signs and symptoms are similar to Prader-Willi syndrome (i.e., patients will have hypotonia, feeding problems in infancy, developmental delay, and short stature), but there will also be relative macrocephaly at birth and body asymmetry.[43]
INVESTIGATIONS
Testing for methylation status reveals hypomethylation at the imprinting control region IG-DMR (intergenic differentially methylated region).
Schaaf-Yang syndrome (MAGEL2-related Prader-Willi-like syndrome)
SIGNS / SYMPTOMS
Signs and symptoms are similar to Prader-Willi syndrome (i.e., poor feeding and hypotonia in infancy) but patients also have joint contractures, and many have severe respiratory insufficiency in infancy, with approximately 20% requiring tracheostomy.
INVESTIGATIONS
MAGEL2 mutation analysis identifies a heterozygous pathogenic variant in the paternally derived MAGEL2 allele.
Myotonic dystrophy
SIGNS / SYMPTOMS
Signs and symptoms are similar to Prader-Willi syndrome (i.e., patients with myotonic dystrophy will also have hypotonia and poor feeding), but patients do not have endocrinopathies.
INVESTIGATIONS
Serum creatinine kinase may be between 50-100 normal levels in Duchenne muscular dystrophy (DMD).
Xp21 mutation may be present in DMD and Becker muscular dystrophy.
Fragile X syndrome
SIGNS / SYMPTOMS
Clinical features may be similar to Prader-Willi syndrome (i.e., behavioral, social, emotional, intellectual challenges, problems with speech and language). However, people with fragile X syndrome may also have a narrow face, large head, large ears, flexible joints, flat feet, and a prominent forehead once they go through puberty, and sensory issues.
INVESTIGATIONS
Genetic testing reveals fragile site on Xp27.3 (FRM1 gene position).
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