The C677T variant in the MTHFR gene is considered to be an associated risk factor for neural tube defects. However, the association has not been found in some ethnic groups. In order to assess the association between neural tube defects and the C677T variant, we determined the frequency of this variant in the MTHFR gene in the State of Yucatan, Mexico, where neural tube defects are highly prevalent. The study was performed on 65 subjects with spine bifida, 60 of their mothers and 110 control subjects. The presence of the C677T variant was determined by amplification and digestion with HinF1 of each subject's DNA. Genotypic and allelic frequencies were calculated for all groups. We did not observe any statistically significant difference in the genotypic or allelic frequencies between cases and controls for any of the groups studied (p > 0.05), suggesting that the thermolabile variant C677T is not an associated risk factor neither for the development of neural tube defects nor for mothers to have affected offspring in the population from Yucatan. Interestingly, the frequency of the C677T variant (54%) obtained in the Yucatan population is one of the highest reported (p < 0.01) and confirmed the high frequency of this allele throughout Mexico.

Most cases of KTW syndrome are sporadic. However, in a few, other family members have some clinical manifestations of the syndrome, and an autosomal dominant mode of inheritance has been suggested. In this paper we present a family with an affected child who has large skin hemangiomata, overgrowth of the right leg, and severe heart defects. Her mother has a large capillary hemangioma on the left side of back and has developed severe varicosities in both lower extremities. The maternal grandmother developed severe varicosities in her legs at a young age. The clinical signs found in the mother represent a milder phenotype and might be explained as variable expressivity of the syndrome. The family tree supports autosomal dominant inheritance. © 1996 Wiley‐Liss, Inc.

The polymorphism A1298C-MTHFR is not associated with NTDs, except for mothers, suggesting only a maternal association with having NTD-affected offspring in the Yucatan population. The frequency of allele C in the control population was 10%, which is significantly lower than in other reported control populations worldwide (p < .01).

We describe an abnormal premature male infant with mosaic monosomy of chromosome 22. He had a unique facial appearance, similar to those with DiGeorge syndrome, and hypertonicity, limitation of extension at major joints, and flexion contractures of all fingers. This rare chromosomal aberration has been reported previously in 6 cases, three of them being nonmosaic and three mosaic patients. There was a great variability of expression among the anomalies of these patients. However, the most common anomalies were in the face and joints. A correlation between the severity of expression and percent of monosomic cells was not clear.

Los avances en el conocimiento de los mecanismos de producción de las enfermedades hereditarias, y la aplicación de los principios de genética en diferentes disciplinas no tratadas de manera común por los genetistas, han ampliado la utilidad del asesoramiento genético. Por estas razones, en la actualidad es mayor el número de familias que buscan asesoría genética por defectos al nacimiento, enfermedades genéticas, así como por causas tan diversas como cáncer, trastornos psiquiátricos, neurodegenerativos, cardiacos, abortos, óbitos, embarazo en edad avanzada, exposición a teratógenos y otros factores de riesgo. El asesoramiento genético es un proceso de comunicación acerca de los problemas humanos asociados con la ocurrencia, o riesgo de ocurrencia y repetición, de un desorden genético familiar. Debe ser proporcionado con imparcialidad, para alcanzar la finalidad de ayudar al individuo, o la familia, para afrontar su situación relacionada con la enfermedad, por medio de información clara para comprender los as pectos médicos, modo de herencia y riesgos de repetición que les permita tomar decisiones razonadas acerca del motivo de su consulta. En esta revisión se abordan los fundamentos en los que se basa el asesoramiento genético, las características de los diferentes modos de herencia tradicionales (herencia mendeliana, cromosómica y multifactorial), novedosos (inestabilidad del genoma, herencia mitocondrial, cambios epigenéticos), y teratogénicos, los principios éticos elementales relacionados con este tema, y se hacen consideraciones acerca de la necesidad de formación de profesionales en salud entrenados para proporcionar consejo genético bajo la supervisión de genetistas clínicos.