autosomal recessive inheritance
Autosomal recessive inheritance is characterised by a disease trait only appearing in the homozygote carrier. Both parents are usually heterozygote carriers for the mutant allele: they are not affected by the disease.
There should be a small risk of offspring acquiring a trait: normal alleleic segregation would predict only 1 in 4 being affected. However, clinically this may not be evident as only families with an affected individual come to attention. Also, these families tend to be ones with large numbers of offspring.
Autosomal recessive diseases affect each sex to equal extents, and when acquired they always present in a stereotyped manner with little variability of expression.
Parental consanguinity may be an important clue to the child carrying an autosomal recessive trait.
A minority of autosomal recessive traits are due to inborn errors of metabolism with defective enzymes. It remains to be confirmed whether this is true for the majority of disorders.
Some autosomal recessive diseases are associated with certain ethnic groups. For example, beta-thalassaemia is associated with Cypriots, Greeks and Italians; Sickle cell disease is associated with African blacks and West Indians; Cystic fibrosis is associated with Caucasians.
Around 1400 autosomal recessive traits are known, the most common ones being: disorder frequency/1000 births
- cystic fibrosis 0.5
- recessive mental retardation 0.5
- congenital deafness 0.2
- phenylketonuria 0.1
- spinal muscular atrophy 0.1
Last reviewed 01/2018