Back to leedsth.nhs.ukLeeds Fetal Medicine Unit Website
Autosomal Recessive:
Autosomal recessive conditions are only manifest as the full phenotype when the individual is homozygous for the mutant allele. Individuals who are heterozygous for the condition often show no features and are completely healthy (carriers), for example, 1 in 25 of the white UK population carries a mutation in one their two cystic fibrosis genes. In some conditions, however, the carrier can show milder features of the disease with carriers of thalassaemia having anaemia. Being heterozygote can be beneficial in some cases, for example, being a carrier for sickle cell disease confers protection against malaria. Autosomal recessive conditions usually arise in a sibling pair rather than in earlier generations of the family.
If parents are related i.e. consanguinous this increases the risk of autosomal recessive conditions as there is more chance of a mutated allele combining with a mutated allele from another family member to result in a homozygous state.
If each parent carries a mutant allele there are three possible outcomes for any offspring. There is a 1 in 4 chance that both mutated alleles will be passed on, resulting in a homozygous and therefore affected individual. There is a 1 in 4 chance that both parents will pass on their normal alleles resulting in an unaffected individual. The final possibility is that one of the mutant alleles would be passed on and the other parent would pass on the normal allele. This could occur from either the maternal or paternal side resulting in a 1 in 2 chance of the resulting offspring being a carrier similar to each of the parents.
Table below shows possible genotypes and phenotypes in two parents who carry an autosomal recessive condition – Image 3
Autosomal Recessive Conditions:
Alkaptonuria |
Ataxia telangiectasia |
β-Thalassaemia |
Congenital adrenal hyperplasia |
Cystic fibrosis |
Dubin-Johnson syndrome |
Fanconi anaemia |
Galactosaemia |
Glucose-6-phosphatase deficiency |
Glycogen storage diseases |
Homocystinuria |
Haemochromatosis |
Oculocutaneous albinism |
Phenylketonuria |
Sickle cell anaemia |
Spinal muscular atrophy |
Tay Sachs disease |
Wilson’s disease |
Autosomal Recessive Family tree
It is not possible to trace this condition through the family tree in contrast to the family tree of autosomal dominant conditions. Only two siblings are affected. These conditions also affect males and females in equal proportions.
If you have techinical problems with this website please contact webmaster@leedsth.nhs.uk.