Cystic Fibrosis: Setting the Scene

Dr. Antoniou puts on the whiteboard a pedigree chart focusing on an autosomal recessive disorder, cystic fibrosis (CF).

Dr. Antoniou: ‘We are shifting from chromosomal abnormalities to a single-gene condition. Let’s discuss this autosomal recessive condition.’

You: ’Can you please remind us what autosomal recessive disease means?’

Ana: ‘If I remember correctly, an autosomal recessive disease is one that manifests clinically when an individual inherits two copies of a mutated allele, one from each parent, on a non-sex chromosome. Heterozygotes, people carrying only one copy of the mutation are typically asymptomatic carriers, while those that are homozygous and have two copies often display the disease phenotype.’

Dr Antoniou: ‘Correct Ana! Before moving on try to identify the phenotype of each individual in the pedigree.’

Dr Antoniou: ‘As an autosomal recessive condition, CF appears when a person inherits one defective CFTR allele from each parent. Let’s look at the second-generation parents 4 and 5.’

What is the next step in this analysis?