Which genetic abnormality accounts for the largest proportion of familial frontotemporal dementia with coexisting amyotrophic lateral sclerosis?

• A Expansion of CGG repeats in the FMR1 gene
• B Trinucleotide CAG expansion in the HTT gene
• C Point mutation in the presenilin-1 gene
• D Hexanucleotide GGGGCC repeat expansion in the C9orf72 gene ✓

Explanation

D hexanucleotide (GGGGCC) repeat expansion in the non-coding region of C9orf72 on chromosome 9 is the most common known mutation in familial frontotemporal dementia and also the leading cause of familial ALS, explaining the frequent overlap of both disorders within families. HTT CAG expansion causes Huntington disease, presenilin mutations cause early-onset Alzheimer disease, and FMR1 CGG expansions cause fragile X syndrome.

Reference: Kaplan and Sadock's Synopsis of Psychiatry, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.