Practice questions › Davidson's Principles of Medicine › Davidson's Medicine - Part 1: Fundamentals of Medicine
03 Clinical genetics MCQs
Davidson's Medicine - Part 1: Fundamentals of Medicine · Davidson's Principles of Medicine · 13 practice questions
- Inheritance
- Imprinting
- Gene expression
- Array CGH
- Classes of variant
- Pharmacogenomics
- Chromosomal disorders
- Cancer predisposition
1. A newborn has a cleft palate, a cardiac outflow tract defect and hypocalcaemia with absent thymic tissue on imaging. Array CGH shows a 22q11.2 microdeletion. Which gene is the major contributor to the cardiac and palatal defects, and what is the mechanism of the deletion?
- AUBE3A, with deletion arising from non-homologous end-joining
- BTBX1, with deletion arising from non-allelic homologous recombination between repeats
- CRAI1, with deletion arising from meiotic non-disjunction
- DElastin, with deletion arising from a triplet repeat expansion
Show answer
B. TBX1, with deletion arising from non-allelic homologous recombination between repeats DiGeorge syndrome features outflow defects, thymic hypoplasia, cleft palate and hypocalcaemia with TBX1 the major gene; most microdeletion syndromes result from non-allelic homologous recombination between similar repeats.
2. A phenotypic male with small testes and gynaecomastia is infertile with high gonadotrophins; a girl has webbed neck, coarctation and primary amenorrhoea. Which karyotypes fit in order?
- A46,XX and 46,XY
- B45,X and 47,XXY
- C47,XYY and 47,XXX
- D47,XXY and 45,X
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D. 47,XXY and 45,X Klinefelter is 47,XXY with hypergonadotropic hypogonadism; Turner is monosomy X affecting about 1 in 2500 live births.
3. Two carriers of the PiM/PiZ alpha-1-antitrypsin phenotype have a child with PiZZ liver disease. In their next pregnancy, and in a pregnancy where one parent has an autosomal dominant condition, which risks apply?
- A1 in 4 and 1 in 4
- B1 in 4 and 1 in 2
- C1 in 2 and 1 in 2
- D1 in 2 and 1 in 4
Show answer
B. 1 in 4 and 1 in 2 Two carrier parents give a 1 in 4 recurrence for an autosomal recessive condition; an affected parent with a dominant condition has a 1 in 2 risk.
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