Title: Fragile (X) X-linked mental retardation. II. Frequency and replication pattern of fragile (X)(q28) in heterozygotes.
Abstract: The frequency of cytologic expression and the replication pattern of the fragile (X) [fra(X)] were investigated in 28 fra(X) heterozygotes, of which 25 agreed to psychological assessment. One-third of the heterozygotes in this study are mentally retarded. The intellectually impaired carriers had a higher frequency of fra(X) and a higher proportion of early-replicating fra(X) than the normally intelligent carriers. The early-replicating fra(X) accounted for 39% of the variability in IQ and the late-replicating fra(X) for 12%. Age had a minimal inverse effect on fra(X) expression and replication pattern. Thus, it appears that mental retardation in females heterozygous for the fra(X) may largely be a function of the proportion of cells with an early-replicating, active X chromosome possessing the fragile site.
Publication Year: 1984
Publication Date: 1984-05-01
Language: en
Type: article
Indexed In: ['pubmed']
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Cited By Count: 33
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