RESUMO
BACKGROUND: Fragile X syndrome is the most frequent cause of inherited mental retardation; it is caused by expansion of CGG repeats in the first exon of the FMR1 gene. Number of CGG repeats varies between 6 and 50 triplets in normal individuals and the most common alleles have 29 or 30 repeats. Allelic patterns in the global population are similar; however, some reports show statistical differences among several populations. Distribution of allelic frequencies for FMR1 locus has not been reported in Mexican population. METHODS: Determination of the CGG repeat number was achieved by polymerase chain reaction (PCR) on modified DNA from 129 unrelated Mexican mestizos (46 FRAXA-negative males with mental retardation and 83 healthy individuals). DNA modification by sodium bisulfite achieves conversion of unmethylated cytosine residues to uracil, which allows efficient amplification by single PCR. Methylation status of FMR1 region for each individual was also established. DNA sequencing of a number of amplified samples was realized to validate the procedure. RESULTS: Molecular analysis of the FMR1 gene showed 23 different alleles. Statistical comparison of allelic length between healthy and affected individuals does not show significant differences. Trinucleotide repeat number varied from 16-40, with modal number of 32 (27.58%), second peak at 30 (25.28%), and minor peak at 34 (10.34%). Together, allelic distribution in the Mexican sample differs significantly from those reported for Caucasian, Chinese, African, Indonesian, Brazilian, Chilean, and Mixtec populations. An excess of large alleles (> or =34 repeats) was evident. CONCLUSIONS: Allele distribution in FMR1 gene from Mexican mestizos is different from that of other reported populations around the world. This unusual modal pattern probably is related to the particular ethnic background of the Mexican population. On the other hand, PCR on modified DNA is a valuable and efficient method for determination of CGG repetitive sequences in FMR1 gene.
Assuntos
Variação Genética , Proteínas do Tecido Nervoso/genética , Proteínas de Ligação a RNA/genética , Alelos , Estudos de Casos e Controles , Ilhas de CpG , Citosina/química , DNA/química , Metilação de DNA , Proteína do X Frágil da Deficiência Intelectual , Síndrome do Cromossomo X Frágil/genética , Frequência do Gene , Humanos , Deficiência Intelectual/genética , Masculino , México , Mutagênese Sítio-Dirigida , Reação em Cadeia da Polimerase , Análise de Sequência de DNA , Sulfitos/farmacologiaRESUMO
Screening for mutations at the G-6-PD gene by PCR-SSCP combined with restriction enzyme analysis and DNA sequencing was performed in nine G-6-PD deficient individuals with negative results for the presence of the most frequent G-6-PD mutations previously observed in Mexican population. The variants G-6-PD Valladolid(406T), G-6-PD Durham(713G), and G-6-PD Viangchan(871A) and four new G-6-PD mutant alleles were identified. The new mutations are located at cDNA nt 376 A --> T (126 Asn --> Tyr), nt 770 G --> T (257 Arg --> Leu), nt 1094 G --> A (365 Arg --> His), and nt 1285 A --> G (429 Lys --> Glu) and they were named G-6-PD San Luis Potosi, G-6-PD Zacatecas, G-6-PD Veracruz, and G-6-PD Yucatán, respectively. To date, a total of 18 different G-6-PD variants have been observed in Mexico and several of them are common in Africa, South Europe, and Southeast Asia.
Assuntos
Testes Genéticos , Glucosefosfato Desidrogenase/genética , Mutação Puntual , Sequência de Bases , Análise Mutacional de DNA , Variação Genética , Humanos , MéxicoRESUMO
Se presentan los resultados del tamizaje para eritroenzimopatías hereditarias en 707 recién nacidos a término con hiperbilirrubinemia (305 niñas y 402 varones), cuyo objetivo fue determinar su frecuencia relativa. Se tamizó por métodos fluorescentes para las eritroenzimopatías más frecuentes a saber: deficiencias de glucosa-6-fosfato deshidrogenasa (G-6-PD), piruvato cinasa (PC) y glucosa fosfatoisomerasa (GPI): estos son tres de los 14 errores congénitos del metabolismo del eritrocito claramente asociados con hemólisis. Se identificaron cuatro varones con deficiencia de G-6-PD y no se encontraron individuos con deficiencia de PC o GPI. Los resultados globales de éste y de estudios previos de nuestro grupo en una población de 2218 individuos sugieren que la frecuencia de la deficiencia de G-6-PD en varones recién nacidos con ictericia y/o hiperbilirrubinemia es de 1.08%. Se concluye que la deficiencia de G-6-PD como causa de hiperbilirrubinemia no es un problema de salud pública en la población estudiada; sin embargo, ya que 1% de los varones con ictericia y/o hiperbilirrubinemia neonatal tienen deficiencia de G-6-PD, se recomienda tomar en consideración este diagnóstico al evaluar a un neonato que presente anemia y/o hiperbilirrubinemia
