This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
Single gene defect ca using multiple unrelated problems - 
Select and explain. 
A. Pleiotropism, B. Pseudodominance, C. Penetrance, D. Anticipation
A: Pleiotropism
Answer: A: Pleiotropism 
Explanation: Ans. is 'a' i.e. Pleiotropy o Pleiotropy occurs when a mutation in a single gene produces effects on more than one characteristic, that is causes multiple mutant phenotypes. o In humans this phenomenon is most obvious when mutations in single genes causes diseases with seemingly unrelated symptoms. Some examles of this phenomenon are : Transcription factor TBx5 mutations that cause the cardiac and limb defects of Holt-Oram syndrome. Glycosylation enzyme MPI mutations that produce the severe mental retardation and blood coagulation abnormalities of type Ib congenital disorders of glycosylation. o DNA damage repair protein NBSI mutations that lead to microcephaly, immunodeficiency and cancer predisposition in Nijmegen breakage syndrome.