A PCR-based test suitable for screening for fragile X syndrome among mentally retarded males |
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Authors: | Luciana A Haddad Regina C Mingroni-Netto Angela M Vianna-Morgante Sérgio D J Pena |
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Institution: | 1. Departamento de Bioqufmica, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Caixa Postal 486, Belo Horizonte, Brazil, 31270-901 2. Departamento de Biologia, Universidade de S?o Paulo, 05422-970, S?o Paulo, Brazil 3. Núcleo de Genética Médica de Minas Gerais (GENE/MG), 30130-909, Belo Horizonte, Brazil
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Abstract: | Ever since the identification of the genetic cause of fragile X syndrome as the expansion of an unstable trinucleotide sequence,
several diagnostic strategies have evolved from molecular studies. However, we still lack a simple test suitable for population
screening. We have therefore developed a nonisotopic polymerase chain reaction (PCR)-based technique for the identification
of fragile X full mutations among men, with easy visualization of the PCR products on silver-stained polyacrylamide gels.
The technique consists of PCR amplification with primers that flank the trinucleotide repeats, with a product of 557 bp for
the (CGG)29 allele. Conditions were established such that full mutations failed to amplify and were thus identified with 98% sensitivity
compared with Southern blot analysis. To produce an indispensable internal control we added to the reaction a third primer,
internal to this fragment, allowing the multiplex amplification of a monomorphic band corresponding to a CG-rich stretch 147
bp upstream of the polymorphic region. In trials involving 41 patients and 74 controls, the PCR-based test here described
showed specificity of more than 98.6%, accuracy of 99% and a sensitivity of 98%. Thus, although not suitable for medical diagnosis,
it constitutes a useful tool for screening for the fragile X syndrome in populations of mentally retarded males.
Received: 31 May 1995 / Revised: 4 October 1995 |
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