Fragile X syndrome is caused by a fragile site at the end of the long arm of X chromosome. Such a disorder is
Fragile X syndrome is caused by a fragile site at the end of the long arm of X chromosome. Such a disorder is
Select an option to attempt
Correct Answer: Option B
Explanation
Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability. Molecular basis: Expansion of a CGG trinucleotide repeat in the 5' UTR of the FMR1 gene on the X chromosome (Xq27.3). Normal: <55 repeats; Premutation: 55–200 repeats; Full mutation: >200 repeats → hypermethylation of FMR1 promoter → gene silencing → loss of FMRP (Fragile X Mental Retardation Protein), an RNA-binding protein regulating synaptic mRNA translation. FXS is X-linked (males hemizygous are more severely affected), caused by loss-of-function of FMR1, and considered dominant in expression (heterozygous females show partial phenotype). All three options in the question are aspects of FXS.