We report three patients with bilateral choanal atresia in children prenatally exposed to methimazole (MMI) in order to define a MMI embryopathy clinical pattern. The combination of choanal atresia and other specific malformations strongly resembles previously reported patients exposed to MMI in utero. At present, propylthiouracil is considered the best treatment in pregnancies. However in Argentina and some other countries MMI is the only antithyroid drug, possibly posing a significant risk to the unborn fetus.

Our patient shows a pattern of anomalies resembling that observed in isotretinoin- and etretinate-exposed children. After ingestion, acitretin is partially converted into etretinate, and etretinate is partially metabolized into acitretin. A similar phenotype would therefore be expected after prenatal exposure to either drug. Moreover, in the present case, teratogenic effects were observed even though the dose was lower than in the previously reported acitretin embryopathy cases. Therefore, we propose that different retinoids, acitretin included, produce only one malformation pattern with variable phenotypic expression.

The isonymy structure of Buenos Aires was studied based on its surname frequency. Information on 2,552,359 voters of the 28 Buenos Aires districts was used to estimate Lasker's coefficient of relationship by isonymy (R(i)), surname diversity according to Fisher's alpha, the coefficient of consanguinity resulting from random isonymy (F), and Nei's, Lasker's and the Euclidean isonymy distances. These distances were correlated with geographic distances, which were calculated by assigning an arbitrary point to each district and measuring distances on a map of the city. The R(i) x 10(5) and F x 10(4) averages of the districts located south of Rivadavia Avenue were higher (R(i) = 66.08; F = 3.4) than those situated north of that avenue (R(i) = 46.60; F = 2.4) (p < 0.001). Fisher's alpha showed the opposite behavior (north, alpha = 1,055.5; south, alpha = 757.2). There was a significant correlation (p < 0.001) between geographic distance and Nei's and the Euclidean distances (0.496 and 0.503, respectively), but the correlation was not significant for Lasker's distance (0.051). These results indicate isolation by distance in the city of Buenos Aires and reveal subdivision of the metropolitan population, with greater consanguinity and a lesser variety of surnames in the districts located in the southern section of the city. This structure agrees with the fragmentation and social, cultural, and economic differences observed among the districts of this Latin American metropolis.

The IMRCM was not significantly associated with the country's marked socioeconomic heterogeneity; the highest %DCM values, on the other hand, were observed in the populations of the central and southern areas of the country. Given the relationship between the %DCM and socioeconomic development of the population, use of this indicator as a proxy of well-being and quality of life is suggested.

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