A premutation is a situation in which there are an excess number of
repeats in a
gene
In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
that is at risk of increasing in length during
reproduction
Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. There are two forms of reproduction: Asexual reproduction, asexual and Sexual ...
but which does not cause disease in the person with the excess number of repeats.
Fragile X syndrome
Fragile X syndrome (FXS) is a genetic neurodevelopmental disorder. The average IQ in males with FXS is under 55, while affected females tend to be in the borderline to normal range, typically around 70–85. Physical features may include a lo ...
, a
trinucleotide repeat disorder
In genetics, trinucleotide repeat disorders, a subset of microsatellite expansion diseases (also known as repeat expansion disorders), are a set of over 30 genetic disorders caused by trinucleotide repeat expansion, a kind of mutation in which ...
, is a condition in which premutations may be present in the parents of affected people.
Huntington's disease
Huntington's disease (HD), also known as Huntington's chorea, is an incurable neurodegenerative disease that is mostly Genetic disorder#Autosomal dominant, inherited. It typically presents as a triad of progressive psychiatric, cognitive, and ...
is another example of a trinucleotide repeat disorder in which individuals with a certain excess of repeats (27–39) of the CAG
codon
Genetic code is a set of rules used by living cells to translate information encoded within genetic material (DNA or RNA sequences of nucleotide triplets or codons) into proteins. Translation is accomplished by the ribosome, which links prote ...
in the
Huntingtin
Huntingtin (Htt) is the protein coded for in humans by the ''HTT'' gene, also known as the ''IT15'' ("interesting transcript 15") gene. Mutation, Mutated ''HTT'' is the cause of Huntington's disease (HD), and has been investigated for this role an ...
gene may not have the disease but are more likely to have a child with enough repeats (40+) to cause the disease.
[{{cite journal, vauthors=Walker FO, date=January 2007, title=Huntington's disease, journal=Lancet, volume=369, issue=9557, pages=218–28, doi=10.1016/S0140-6736(07)60111-1, pmid=17240289, s2cid=46151626]
References
Mutation