The correct answer is C. Telomerase complex
Correct Answer Explanation
The correct answer is the telomerase complex (Choice 3), as this case represents dyskeratosis congenita. Dyskeratosis congenita occurs due to mutations in TERT (AD/AR), TERC (AD), DKC1 (XLR), or TINF2 (AD) genes which encode for proteins involved in telomere maintenance. Affected patients manifest reduced telomerase activity and abnormally shortened telomeres leading to chromosomal instability and cellular replication dysfunction. Clinical features include bone marrow failure and the triad of abnormal reticulated hyperpigmentation on the face/neck/upper trunk, oral leukoplakia (premalignant), and onychodystrophy (pterygium, anonychia, longitudinal ridging/splitting).
Incorrect Answer Explanation
Multiple endocrine neoplasia (MEN) type 2 is due to a mutation in the RET proto-oncogene, which encodes for a tyrosine kinase receptor (Choice A). Noonan syndrome is due to a mutation in PTPN11, which encodes a protein tyrosine-protein phosphatase (Choice B). Rothmund-Thompson Syndrome is due to a mutation in RecQL4, which encodes a DNA helicase (Choice D). Progeria is due to a mutation in Lamin A, which encodes a nuclear envelope protein (Choice E).
Bolognia, Jean., Jorizzo, Joseph L.Schaffer, Julie V. (Eds.) (2012) Dermatology /[Philadelphia]: Elsevier Saunders; Savage, S. and Alter, B. (2019). Dyskeratosis Congenita. [online] Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2702847/