The parents of a 3-year-old boy with cystic fibrosis ask for advice. They are considering having more children.
What is the chance that their next child will be a carrier of the cystic fibrosis gene?
Correct Answer A: As cystic fibrosis is an autosomal recessive condition there is a 50% chance that their next child will be a carrier of cystic fibrosis (i.e. be heterozygous for the genetic defect) and a 25% chance that the child will actually have the disease (be homozygous).
Cystic fibrosis: Cystic fibrosis (CF) is an autosomal recessive disorder causing increased viscosity of secretions (e.g. lungs and pancreas). It is due to a defect in the cystic fibrosis transmembrane conductance regulator gene (CFTR), which codes a cAMP-regulated chloride channel In the UK 80% of CF cases are due to delta F508 on the long arm of chromosome 7. Cystic fibrosis affects 1 per 2500 births, and the carrier rate is c. 1 in 25.
Organisms which may colonize CF patients:
*previously known as Pseudomonas cepacia
What does troponin T bind to?
Correct Answer A: Tropomyosin is a protein which regulates actin. It associates with actin in muscle fibres and regulates muscle contraction by regulating the binding of myosin.
Cardiac enzymes and protein markers: Interpretation of the various cardiac enzymes has now largely been superceded by the introduction of troponin T and I. Questions still however commonly appear in the MRCP Key points for the exam:
Acute intermittent porphyria is due to a defect in:
Correct Answer E: AIP - porphobilinogen deAminase; PCT - uroporphyrinogen deCarboxylase.
Porphyrias: Overview:
1- Acute intermittent porphyria (AIP):
2- Porphyria cutanea tarda (PCT):
3- Variegate porphyria:
Which one of the following pathophysiological changes is most responsible for emphysema?
Correct Answer B: Proteinases such as elastase cause irreversible damage to the supporting connective tissue of the alveolar septa. Smoking accelerates this process.
COPD: causes:
A 17-year-old man is investigated for recurrent infections and easy bruising. In the past year he has had four episodes of pneumonia. Other than the bruising he is noted to have severe eczema on his trunk and arms. A full blood count is ordered and reported as follows:
Further bloods show low immunoglobulin M levels.
What is the most likely diagnosis?
Correct Answer B:
Wiskott-Aldrich syndrome:
Wiskott-Aldrich syndrome: Wiskott-Aldrich syndrome causes primary immunodeficiency due to a combined B- and T-cell dysfunction. It is inherited in a X-linked recessive fashion and is thought to be caused by mutation in the WASP gene.
Features:
Click to expand