RESUMO
BACKGROUND AND PURPOSE: The presence of cell-free fetal DNA in maternal plasma could allow performing a non-invasive prenatal diagnosis of Huntington disease (HD). The great advantage of this diagnosis is the absence of risk of fetal loss that it entails. METHODS: Maternal plasma from four pregnant women in their first trimester of gestation with a fetus at-risk was studied. In all the four cases, the father was affected. RESULTS: The diagnosis was performed both by a direct study of the mutation and an indirect haplotype study. By the direct analysis, three out of the four fetuses could be correctly diagnosed whilst the indirect analysis was only conclusive in one case. CONCLUSIONS: Non-invasive prenatal diagnosis of HD is possible by the analysis of fetal DNA in maternal plasma. Direct analysis of the mutation has shown higher accuracy than the haplotype analysis except for long expansions. Haplotype analysis would need to be improved for the study of Juvenile-onset HD. This diagnostic method would be limited to those couples with an affected male however this situation represents 80-90% of the pregnancies at-risk of HD. Moreover, it could be used as a confirmation test of healthy embryos transferred on pre-implantation genetic studies of HD.
Assuntos
DNA/sangue , Doença de Huntington/diagnóstico , Diagnóstico Pré-Natal/métodos , Análise Mutacional de DNA/métodos , Feminino , Frequência do Gene , Predisposição Genética para Doença , Haplótipos , Humanos , Proteína Huntingtina , Doença de Huntington/genética , Padrões de Herança , Masculino , Repetições de Microssatélites , Mutação , Proteínas do Tecido Nervoso/genética , Proteínas Nucleares/genética , Linhagem , Valor Preditivo dos Testes , Gravidez , Primeiro Trimestre da Gravidez/sangue , Prognóstico , Repetições de TrinucleotídeosRESUMO
PURPOSE: Stargardt disease (STGD) is the most common juvenile macular dystrophy, characterized by central visual impairment. All recessively inherited cases are thought to be due to mutations in the ABCA4 gene, mapped to 1p21-p13. METHODS: To describe a form of non-mendelian inheritance in a patient with STGD identified through the course of a conventional mutational screening performed on 77 STGD families. DNA from the patient and relatives was analyzed for variants in all 50 exons of the ABCA4 gene by screening on the ABCR400 microarray; results were confirmed by direct sequencing. Haplotype analyses, standard and high-resolution (HR) karyotypes, and multiplex ligation-dependent probe amplification (MLPA) were also performed. RESULTS: A patient with STGD caused by the homozygous p.Arg1129Leu mutation in the ABCA4 gene was found to be the daughter of a noncarrier mother and a father who was heterozygous for this change. Haplotype analysis suggested that no maternal ABCA4 allele was transmitted to the patient. Microsatellite markers spanning the entire chromosome 1 identified a homozygous region of at least 4.4 Mb, involving the ABCA4 gene. The cytogenetic study revealed normal female karyotype. Further evaluation with MLPA showed the patient had a normal dosage for both copies of the ABCA4 gene, thus suggesting partial paternal isodisomy but not a maternal microdeletion. CONCLUSIONS: We report that recessive STGD can rarely be inherited from only one unaffected carrier parent in a non-mendelian manner. This study also demonstrates that genomic alterations contribute to only a small fraction of disease-associated alleles for ABCA4.