Which two disorders are classic examples of imprinting disorders on chromosome 15?

Which two disorders are classic examples of imprinting disorders on chromosome 15?

• A. Prader-Willi syndrome and Angelman syndrome
• B. Angelman syndrome and Down syndrome
• C. Cri-du-chat syndrome and Patau syndrome
• D. Williams syndrome and Prader-Willi syndrome

Answer: (B)

Imprinting on chromosome 15 means certain genes are expressed only from one parent’s chromosome. In the 15q11-q13 region, two disorders show the opposite parent-of-origin expression: Prader-Willi syndrome results when paternal gene expression is missing, while Angelman syndrome results when maternal gene expression is missing. The underlying mechanisms include deletions or uniparental disomy that disrupt the appropriate parent-specific expression. Clinically, this pair is classic because they arise from the same chromosomal region but from opposite parental imprints. Down syndrome, by contrast, is due to trisomy 21 and is not an imprinting disorder, so it isn’t the example here.

Imprinting on chromosome 15 means certain genes are expressed only from one parent’s chromosome. In the 15q11-q13 region, two disorders show the opposite parent-of-origin expression: Prader-Willi syndrome results when paternal gene expression is missing, while Angelman syndrome results when maternal gene expression is missing. The underlying mechanisms include deletions or uniparental disomy that disrupt the appropriate parent-specific expression. Clinically, this pair is classic because they arise from the same chromosomal region but from opposite parental imprints. Down syndrome, by contrast, is due to trisomy 21 and is not an imprinting disorder, so it isn’t the example here.