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Student Education

Picture Quiz: The genetics of cystic fibrosis

BMJ 2003; 327 doi: https://doi.org/10.1136/sbmj.0311405 (Published 01 November 2003) Cite this as: BMJ 2003;327:0311405
  1. Bruno Rushforth, final year medical student1,
  2. Usha Kini, specialist registrar in clinical genetics2
  1. 1University of Manchester
  2. 2St Mary's Hospital, Manchester

Case history

Mr and Mrs A attend your paediatric clinic with their 18 month old daughter. She has a history of repeated chest infections, failure to thrive, and steatorrhoea (fatty stools). As part of the consultation you take a family history and draw the pedigree (family tree) (fig 1).

Fig 1

Family tree

Questions

  1. What does the double line between Mr and Mrs A represent?

  2. You suspect an inherited disorder. Examining the pedigree, what is the most likely pattern of inheritance--sex linked, autosomal dominant, or autosomal recessive?

  3. What is the most likely diagnosis?

  4. Given that Mr and Mrs A's first child--an 8 year old boy--is fit and well, what is the probability that he is a carrier of the inherited disorder?

  5. While at clinic, Mrs A tells you that she is pregnant and is worried that the child could also be affected by the same condition. Who would you refer her to and why?

Answers

  1. Consanguinity, which means “of the same blood.” Mr and Mrs A are genetically related as they share a common set of grandparents--they are first …

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