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Zorluk: OrtaGenetic and Molecular Mechanisms

Match each clinical presentation described below with its primary underlying genetic or molecular pathophysiologic mechanism.

  • A 9-year-old girl with severe facial freckling and multiple basal cell carcinomas on sun-exposed skin areas.Inability to remove bulky DNA adducts and pyrimidine dimers via nucleotide excision repair.
  • A 42-year-old man with progressive choreiform movements, behavioral changes, and caudate nucleus atrophy.Trinucleotide repeat expansion resulting in a toxic gain-of-function protein with abnormal folding.
  • A 7-year-old boy with progressive cerebellar ataxia, recurrent sinopulmonary infections, and conjunctival vascular lesions.Failure to recognize and repair DNA double-strand breaks via nonhomologous end joining.
  • A 24-year-old man with tall stature, ectopia lentis, and echocardiographic evidence of aortic root dilation.Production of a mutant glycoprotein that disrupts microfibril assembly and causes excessive TGF-beta signaling.

Cevap

The presentations map to their respective molecular defects: Xeroderma pigmentosum corresponds to defective nucleotide excision repair; Huntington disease to toxic gain-of-function from trinucleotide expansion; Ataxia-telangiectasia to impaired nonhomologous end joining; and Marfan syndrome to mutant glycoprotein causing excessive TGF-beta signaling.
Each clinical vignette maps directly to a unique molecular pathway defect. Xeroderma pigmentosum results from a failure to repair UV-induced pyrimidine dimers via nucleotide excision repair. Huntington disease is caused by CAG trinucleotide repeat expansion, leading to a toxic gain-of-function huntingtin protein. Ataxia-telangiectasia is due to ATM gene mutations, disrupting the nonhomologous end joining repair of double-strand DNA breaks. Marfan syndrome is caused by FBN1 mutations, producing abnormal fibrillin-1 that fails to regulate TGF-beta signaling appropriately.

Adım Adım Çözüm

1
Identify the clinical syndrome described in each vignette on the left.
The vignettes represent Xeroderma pigmentosum, Huntington disease, Ataxia-telangiectasia, and Marfan syndrome, respectively.
Accurate clinical diagnosis is the required first step before mapping the phenotype to a molecular defect.
2
Determine the specific genetic or molecular abnormality underlying each identified condition.
Xeroderma pigmentosum involves nucleotide excision repair; Huntington disease involves a polyglutamine tract causing protein misfolding; Ataxia-telangiectasia involves the ATM gene and nonhomologous end joining; Marfan syndrome involves fibrillin-1 and TGF-beta dysregulation.
Matching the clinical syndrome to its fundamental pathophysiology tests the core genetic mechanisms.

Anahtar Kavram

Understanding the precise molecular and genetic mechanisms underlying distinct clinical phenotypes is essential for accurate diagnosis and management of inherited disorders.
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Konular

Genetic and Molecular Mechanisms

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