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What is the function of the affected gene in Cowden syndrome?

A. Gap junction protein

B. Tumor suppressor gene

C. Transcription factor

D. Growth factor receptor

B. Cowden syndrome is associated with mutations in PTEN, a tumor suppressor gene. Mutations in gap junction proteins are associated with hidrotic ectodermal dysplasia, erythrokeratoderma variabilis, and Vohwinkel syndrome.

Which of the following displays an autosomal recessive pattern of inheritance?

A. Bullous ichthyosiform erythroderma

B. Weber-Cockayne syndrome

C. White sponge nevus

D. Epidermolysis bullosa, junctional

D. Junctional epidermolysis bullosa results from mutations in laminin 5 or α6β4 integrin and displays and autosomal recessive pattern of inheritance. Bullous ichthyosiform erythroderma (epidermolytic hyperkeratosis), Weber-Cockayne syndrome (epidermolysis bullosa simplex), and white sponge nevus are due to mutations in keratins and are thus inherited in an autosomal dominant manner.

Which of the following involves a defective enzyme located in mitochondria?

A. Porphyria cutanea tarda (PCT)

B. Porphyria, acute intermittent (AIP)

C. Porphyria, erythropoietic protoporphyria (EPP)

D. Hepatoerythropoietic porphyria (HEP)

C. EPP is due to mutations in ferrochelatase, an enzyme present in mitochondria. Variegate porphyria is due to mutations in protoporphyrinogen oxidase, also present in mitochondria. The other porphyrias listed are due to mutations affecting cytoplasmic enzymes.

Which of the following diseases is NOT due to a defective DNA helicase?

A. Rothmund-Thomson (poikiloderma congenitale)

B. Trichothiodystrophy

C. Ataxia-telangiectasia (Louis-Bar syndrome)

D. Bloom syndrome

C. Ataxia-telangiectasia (Louis-Bar syndrome) is an autosomal recessive disease due to mutations in the ATM gene. Bloom syndrome, Cockayne syndrome, Rothmund-Thomson syndrome, Werner syndrome, and Trichothiodystrophy/PIBIDS are due to mutations in DNA helicases.

What is the function of the defective gene product in Dyskeratosis congenita?

A. Ribosomal RNA synthesis

B. Telomerase

C. Mismatch repair

D. Both A and B

D. DKC1 and TERC are genes involved in ...

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