ABD Genodermatoses and Nevi 2 — Questions and Answers
Question 1: Neurofibromatosis type 1 is caused by a mutation in which gene?
- NF1 (neurofibromin) (Correct answer)
- NF2 (merlin)
- TSC1 (hamartin)
- PTEN
Correct answer: NF1 (neurofibromin)
NF1 results from loss-of-function mutations in the NF1 gene encoding neurofibromin, a RAS-GTPase-activating protein.
Question 2: Which diagnostic criterion requires at least six lesions greater than 5 mm (prepubertal) in neurofibromatosis type 1?
- Café-au-lait macules (Correct answer)
- Lisch nodules
- Optic gliomas
- Axillary freckling
Correct answer: Café-au-lait macules
Six or more café-au-lait macules >5 mm prepubertal (>15 mm postpubertal) is a hallmark NIH diagnostic criterion for NF1.
Question 3: Ash-leaf macules (hypopigmented spots best seen with Wood lamp) are an early sign of which genodermatosis?
- Tuberous sclerosis complex (Correct answer)
- Neurofibromatosis type 1
- Incontinentia pigmenti
- Xeroderma pigmentosum
Correct answer: Tuberous sclerosis complex
Ash-leaf (lance-ovate) hypopigmented macules are one of the earliest cutaneous findings in tuberous sclerosis complex.
Question 4: The facial angiofibromas of tuberous sclerosis were historically misnamed as what?
- Adenoma sebaceum (Correct answer)
- Acne rosacea
- Trichoepitheliomas
- Syringomas
Correct answer: Adenoma sebaceum
The angiofibromas of tuberous sclerosis were long called 'adenoma sebaceum,' a misnomer since they are not of sebaceous origin.
Question 5: A collagenous connective tissue nevus presenting as a leathery plaque over the lumbosacral area in tuberous sclerosis is called a:
- Shagreen patch (Correct answer)
- Peau d'orange
- Café-au-lait macule
- Nevus anemicus
Correct answer: Shagreen patch
The shagreen patch is a connective tissue nevus (collagenoma) classically located on the lower back in tuberous sclerosis.
Question 6: Periungual fibromas (Koenen tumors) around the nails are a diagnostic feature of which condition?
- Tuberous sclerosis complex (Correct answer)
- Neurofibromatosis type 2
- Gardner syndrome
- Cowden syndrome
Correct answer: Tuberous sclerosis complex
Koenen tumors are periungual/subungual fibromas that typically appear in adolescence in tuberous sclerosis.
Question 7: Bilateral vestibular schwannomas are the hallmark of which neurocutaneous disorder?
- Neurofibromatosis type 2 (Correct answer)
- Neurofibromatosis type 1
- Sturge-Weber syndrome
- von Hippel-Lindau disease
Correct answer: Neurofibromatosis type 2
Bilateral acoustic (vestibular) schwannomas define neurofibromatosis type 2, caused by NF2/merlin mutations.
ABD Genodermatoses and Nevi 2
Neurofibromatosis type 1 is caused by a mutation in which gene?