The nurse explains to the parents of a child with Prader-Willi syndrome that this disease is caused by:
A) genetic imprinting.
B) mosaicism.
C) single-nucleotide polymorphism (SNP).
D) missense mutation.
A) genetic imprinting.
Explanation: A) In genetic imprinting, some genes have differential expression based on the parent from whom the genes are inherited. For example, a deletion of a portion of chromosome 15 leads to a disorder called Prader-Willi syndrome when inherited from the father, but the same gene deletion leads to a different condition called Angelman syndrome when inherited from the mother.
B) Nondisjunction can occur during meiosis (creation of sperm and egg cells). This can also occur shortly after conception, causing the presence of more than one genetic cell line in a person, a condition called mosaicism. The clinical effects of the mosaicism often depend on how many abnormal cells are present, but this is not the cause of Prader-Willi syndrome.
C) Not all genetic changes among individuals are pathogenic. When present in at least 1% of the population, a change is referred to as a single-nucleotide polymorphism (SNP). Some polymorphisms may just result in human variation with no clinical impact at all; others may contribute to disease, but this is not the cause of Prader-Willi syndrome.
D) A missense mutation causes a change in the amino acid sequence, but this is not the cause of Prader-Willi syndrome.
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