premutation


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premutation

(pre?mu-ta'shun)
A sequence of multiply repeated nucleotides that may produce a disease in one's offspring but may not produce clinically apparent disease in the carrier. A common premutation occurs in the Fragile X syndrome, in which ancestors of affected children may have 50 — 200 copies of the trinucleotide sequence CGG. These individuals do not have the full phenotypic expression of the Fragile X syndrome but as adults may suffer Parkinson-like movement disorders such as ataxia and tremors.
Synonym: intermediate allele

Premutation

A change in a gene that precedes a mutation; this change does not alter the function of the gene.
Mentioned in: Fragile X Syndrome
References in periodicals archive ?
Also, we would like to emphasize the importance of identifying and diagnosing affected individuals with a premutation and a full mutation without phenotype for genetic counseling and education on associated pathologies.
The carriers of the premutation alleles can exhibit 3 clinical forms, i.
In every pooling variant and PCR triplicate we were able to correctly determine the diagnostic classification (normal, intermediate, premutation, full mutation) and in each case determine the major expansion size, defined as the largest peak when assayed individually (Table 1).
Expanded CGG triplets in the premutation range (55-200 CGG) in the FMRI gene are responsible for this syndrome (2,3,4,5).
Many laboratories incorrectly identified samples with 42 repeats as gray-zone or premutation.
Using a newly available and cost-effective screening test, the study offered voluntary NBS for both the fragile X full mutation and premutation.
Diagnostic testing revealed heterozygosity for a Fragile X syndrome premutation (CGG repeat length 31 for the normal allele; 72 for the premutation allele).
Like those with the full mutation, premutation carriers have an abnormal number of repeats, yet fewer than are typically required to cause fragile-X syndrome.
A review of fragile X premutation disorders: expanding the psychiatric perspective.
The frequency of this pattern determines if an individual has a premutation or a full mutation.