Autosomal Recessive Genetic Disorders ✅

Question 1

What are autosomal recessive disorders caused by?

Answer 1

‘Biallelic’ mutations affecting both copies (alleles) of a gene on an autosomal dominant chromosome

Question 2

What is meant by homozygous with respect to autosomal recessive disorders?

Answer 2

Both alleles have the same mutation

Question 3

What is meant by compound heterozygous with respect to autosomal recessive disorders?

Answer 3

The two alleles have different mutations

Question 4

Give 6 examples of autosomal recessive conditions

Answer 4

• Sickle cell disease
• Thalassaemia’s
• Spinal muscular atrophy
• Phenylketonuria
• MCAD deficiency
• Many inborn errors of metabolism

Question 5

When are autosomal dominant conditions more common?

Answer 5

When parents are related

Question 6

What is the incidence of cystic fibrosis?

Answer 6

1 in 2500

Question 7

What causes cystic fibrosis?

Answer 7

Biallelic mutations in the CFTR gene

Question 8

What is the carrier frequency of CFTR mutations in Western Europeans?

Answer 8

1 in 25

Question 9

What accounts for the vast majority of CFTR mutations in Western Europeans?

Answer 9

A number of ‘founder’ mutations

Question 10

What % of CFTR mutations are detected by targeted testing for the 9 most common mutations?

Answer 10

95%

Question 11

When is targeted mutation testing less effective for cystic fibrosis?

Answer 11

In other populations

Question 12

What is sometimes required to detect the CFTR mutation in cystic fibrosis?

Answer 12

Extended mutation testing and/or sequencing of the whole gene

Question 13

What are families in which a case or carrier of cystic fibrosis is identified offered?

Answer 13

‘Cascade’ carrier testing

Question 14

What happens in ‘cascade’ carrier testing?

Answer 14

Partners of carriers are offered carrier testing to identify couples at risk of having an affected child