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Question 579

Genetics → General

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Classification

Speciality
Obstetrics and Gynaecology
Group
Basic
Title
Genetics
Topic
General
Subtopic 1
Deoxyribonucleic Acid
Subtopic 2
Trinucleotide repeat abnormalities
Subtopic 3
Associated disorder group
Question Type
SBA

Question

SSBA
Question Header
Which group of disorders most directly fits the molecular abnormality being investigated?
Question Stem
A molecular genetics investigation focuses on abnormalities in repeated DNA units, each consisting of three nucleotides. The investigators want a group of disorders sharing this association, rather than a group selected only for neurological or muscular manifestations.

Options

A Huntington's disease, fragile X syndrome and myotonic dystrophy
B Kearns–Sayre syndrome, Leber's hereditary optic neuropathy and cytochrome c oxidase deficiency
C Cystic fibrosis, Wilson's disease and Gaucher's disease
D Huntington's disease, Kearns–Sayre syndrome and myotonic dystrophy
E Fragile X syndrome, Leber's hereditary optic neuropathy and myotonic dystrophy

Explanation

The repeated three-nucleotide units are trinucleotide repeats. Abnormalities of these repeat sequences are associated with Huntington's disease, fragile X syndrome and myotonic dystrophy. A shared neurological or muscular presentation does not establish this mechanism: mitochondrial DNA disorders form a separate molecular group.

Option Validity

B) These are mitochondrial DNA-associated conditions, rather than the trinucleotide-repeat disorder group required by the investigation.

C) These disorders share autosomal recessive inheritance; that category does not establish the specified trinucleotide-repeat mechanism.

D) Huntington's disease and myotonic dystrophy fit, but Kearns–Sayre syndrome belongs to the mitochondrial group.

E) Fragile X syndrome and myotonic dystrophy fit, but Leber's hereditary optic neuropathy belongs to the mitochondrial group.

Further Reading

Saxena R. Textbook for MRCOG-1: Basic Sciences in Obstetrics and Gynaecology. 1st ed. Jaypee Brothers Medical Publishers; 2016. Chapter 8: Genetics — Deoxyribonucleic Acid; Mitochondrial DNA; Table 8.1. Printed pages 254–256 and 258.

Source & metrics

Authored Difficulty
4.00
Evaluation Score
—
Destination
eBook
Source
Saxena - MRCOG-1 Basic Sciences - Genetics
Source Section
Chapter 8 — Genetics — Deoxyribonucleic Acid; Mitochondrial DNA
Source Locator
Printed pages 254–256 and 258
Updated
2026-10-06 01:57:35
Difficulty Factor
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