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Down syndrome (DS) is a complex genetic and metabolic disorder attributed to the presence of three copies of chromosome 21. The extra chromosome derives from the mother in 93% of cases and is due to abnormal chromosome segregation during meiosis (nondisjunction). Except for advanced age at conception, maternal risk factors for meiotic nondisjunction are not well established. A recent preliminary study suggested that abnormal folate metabolism and the 677 (C-->T) mutation in the methylene-tetrahydrofolate reductase (MTHFR) gene may be maternal risk factors for DS. Frequency of the MTHFR 677 (C-->T) and 1298 (A-->C) mutations was evaluated in 36 mothers of children with DS and in 200 controls. The results are consistent with the observation that the MTHFR 677 (C-->T) and 1298 (A-->C) mutations are more prevalent among mothers of children with DS than controls. In addition, the most prevalent genotype was the combination of both mutations. The results suggest that mutations in the MTHFR gene are associated with maternal risk for DS

We report on a 5-year-old girl with a male karyotype (46,XY), severe psychomotor and physical retardation, minor anomalies, and female external genitalia with a blindly ending vagina. She has normal adrenal function, prepubertal serum gonadotropin and testosterone levels, which did not rise after hCG stimulation. On abdominal exploration no gonads were found, and only mesonephric and Müllerian remnants. She was HY positive, and no deletion was detected in the Y chromosome using 5 different probes. Although a genetic defect is not excluded, pregnancy complications suggest an environmental insult to the developing testes.

Cystic fibrosis is an autosomal recessive disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator gene. This disorder produces a variable phenotype including lung disease, pancreatic insufficiency, and meconium ileus plus bilateral agenesis of the vas deferens causing obstructive azoospermia and male infertility. Preimplantation genetic diagnosis is an alternative that allows identification of embryos affected by this or other genetic diseases. We report a case of couple with cystic fibrosis; the woman had the I148 T mutation and the man had the Delta F508 gene mutation. The couple underwent in vitro fertilization, associated with preimplantation genetic diagnosis, and with subsequent selection of healthy embryos for uterine transfer. The result was an uneventful pregnancy and delivery of a healthy male baby.