Which of the following is true of Fragile X syndrome?

Question

Quizplus · Accepted Answer

Fragile X syndrome is almost always caused by a trinucleotide expansion (CGG) in the 5' untranslated region of the FMR1 gene on the X chromosome. This expansion leads to methylation and decreased expression of the FMR1 gene, resulting in the clinical features of Fragile X syndrome.

Answer: A
 Testicular atrophy is a common feature of Fragile X syndrome in males, and typically begins during puberty. However, not all males with Fragile X syndrome will have testicular atrophy.

Answer: B
 Accurate prenatal diagnosis of full-mutation females with Fragile X syndrome is available through chorionic villus sampling or amniocentesis. However, accurate prenatal diagnosis for males with Fragile X syndrome is not currently available.

Answer: D
 Expansion of premutation CGG repeats in FMR1 occurs primarily during oogenesis in women. In males, expansion of CGG repeats can occur during both spermatogenesis and post-zygotic mitotic amplification. Premutation carriers may also show phenotypic effects, such as Fragile X-associated tremor/ataxia syndrome (FXTAS) in older individuals.

Which of the Following Is True of Fragile X Syndrome