Genomic Imprinting Disorders

Multiple Choice Questions in Neurology:

Somatic cells form by two copies of alleles during the fertilization, one copy inherited from each parent. However, if gene expression occurs from only one allele i.e. one parent, is called genomic imprinting. Which of the following is/are associated with genomic imprinting disorders?
  1. Fragile X Syndrome
  2. Angelman Syndrome
  3. Myotonic Dystrophy
  4. Prader Willi Syndrome
  5. Huntington's Disorder

Genomic Imprinting Disorders

Normally, somatic cells form by two copies of alleles during the fertilization, one copy inherited from each parent. However, if gene expression occurs from only one allele i.e. one parent, is called genomic imprinting. Epigenetic phenomena do not involve alterations in the DNA sequence. It usually affects functional activity and expression of genes. Genomic imprinting is an epigenetic phenomena. Imprinted alleles/genes of the parent are silent. Only non-imprinted alleles/genes of parents are expressed in children. Imprinted alleles/genes may be paternal (father) or maternal (mother). Genomic imprinting does not follow Mendelian Inheritance Law.

Diseases Related to Imprinting

  • Prader-Willi syndrome (Long arm of chromosome 15q11-13) => Paternal Inheritance
  • Angelman syndrome (Long arm of chromosome 15q11-13) => Maternal Inheritance
  • Beckwith-Wiedemann syndrome (Chromosome 11p15.5)
  • Silver-Russell syndrome (Chromosome 11p15.5)
Note:
  • Prader-Willi syndrome : Paternal Inheritance (P:P)
  • Angelman syndrome : Angel => Female : Maternal Inheritance
  • Both Prader-Willi syndrome and Angelman syndrome are associated with mutation in the long arm of chromosome 15q11-13.

References:

  • Ferguson-Smith, Anne C. "Genomic imprinting: the emergence of an epigenetic paradigm." Nature Reviews Genetics 12.8 (2011): 565-575.
  • Marques, Cristina Joana, et al. "Genomic imprinting in disruptive spermatogenesis." The lancet 363.9422 (2004): 1700-1702.
  • Hall, Judith G. "Genomic imprinting: review and relevance to human diseases." American journal of human genetics 46.5 (1990): 857.
  • Brannan, Camilynn I., and Marisa S. Bartolomei. "Mechanisms of genomic imprinting." Current opinion in genetics & development 9.2 (1999): 164-170.
[Answers are B. Angelman Syndrome, D. Prader Willi Syndrome]

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