Bernardo Beiguelman

Medical genetic services in Latin America: report of a meeting of experts

During the Ninth International Congress of Human Genetics which was held in Rio de Janeiro, Brazil, from 16 to 18 August 1996, a group of experts under the coordination of the authors discussed at length the state of medical genetics in Latin America. The facts and ideas presented at the meeting, which was sponsored by the Human Genetics Program of the World Health Organization (WHO) and the Maternal and Child Health Program of the Pan American Health Organization, are examined in this document under three broad headings. The first verses on the history and current status of medical genetics in selected Latin American countries. This is followed by a discussion of the general features of medical genetics in the Region and by a final section of recommendations for promoting medical genetics in Latin America.

TASTE SENSITIVITY TO PHENYLTHIOUREA AMONG PATIENTS AFFECTED WITH BOTH TUBERCULOSIS AND LEPROSY.

Taste thresholds for phenylthiourea were measured among 58 Caucasoid subjects affected with both tuberculosis and leprosy. The frequency of non-tasters among them (12.1%) is significantly lower than that found among healthy controls (24.7%) but not different from the frequency of non-tasters among tuberculous patients (14.1%) or leprous patients (19.6%). These results suggest a correlation between taste ability to phenylthiourea and the constitutional susceptibility to tuberculosis and leprosy.

Birth weight of twins: 1. The fetal growth patterns of twins and singletons

As distribuicoes dos pesos de recem-nascidos de partos gemelares e unicos em tres maternidades do sudeste brasileiro foram comparadas, depois do ajustamento desses pesos a idade gestacional, seus termos quadratico e cubico, sexo e tipo de gestacao e as interacoes dessas variaveis. O padrao da taxa de crescimento fetal dos gemeos em comparacao ao dos recem-nascidos de parto unico e retardado, independentemente do nivel socio-economico da populacao examinada, mas a idade gestacional em que comeca esse atraso parece estar correlacionada ao nivel economico das maes. Em todos os casos, depois de 28 semanas de gestacao, o crescimento dos fetos femininos mostrou-se levemente, mas consistentemente, inferior ao dos fetos masculinos.

Birth weight of twins: 2. Fetal genetic effect on birth weight

Os coeficientes de correlacao intraclasse foram calculados para o peso de gemeos nascidos em tres maternidades do sudeste brasileiro, depois de ajustar os logaritmos naturais desses pesos para a idade gestacional, seus termos quadratico e cubico, sexo e interacoes dessas variaveis. Os dados obtidos indicaram que o efeito genetico fetal sobre o peso ao nascer teria a oportunidade de ser demonstrado por recem-nascidos de maes subnutridas. A subnutricao, atuando como forca seletiva, realcaria a existencia de genotipos que determinam menor necessidade nutricional para o desenvolvimento normal.

Maternal age and Down syndrome in Southeastern Brazil

The proportion of maternal-age-independent patients estimated among 200 Brazilian Down syndrome children (59.6%) was significantly larger than that of maternal-age-dependent cases (40.4%). The latter proportion is the smallest observed in pertinent literature and due basically to the low mean maternal age of the population analyzed. Based on the remarkable correlation (r = 0.95) between the proportion of maternal-age-dependent patients and the mean maternal age of the general population, a simple predictive equation to estimate the proportion of maternal-age-dependent Down syndrome patients based on the mean maternal age of the general population is suggested in situations where reliable data on the incidence of this syndrome according to maternal age is not available.

TWINNING RATE IN A SOUTHEASTERN BRAZILIAN POPULATION

The twinning incidence from 1984 to 1993 was investigated in Campinas, State of São Paulo, Brazil and the analyzed data were combined with previous series from the same population. This study has shown that the mean annual incidences and the standard deviations for DZ, MZ and DZ plus MZ twins for the period of 1984 to 1993 are estimated respectively as 4.7 +/- 0.92, 4.1 +/- 1.11, and 8.8 +/- 0.87 per 1,000. In the same period the mean annual incidence of triplets was 0.15 +/- 0.16. It was also shown that the incidence of DZ twins is steadily decreasing since 1925, while the incidence of MZ pairs, after a period of decline is increasing since the sixties, due perhaps to the widespread use of oral contraceptives. Concerning the twinning rate as a whole, it has been shown that its declining trend has disappeared over the last few years.

TASTE SENSITIVITY TO PHENYLTHIOUREA AND MENSTRUATION.

Taste thresholds for phenylthiourea were measured among 100 females, during the menstruation and in non-menstrual period. The results cannot support any influence of menstruation on taste threshold for phenylthiourea.

INVESTIGATION ON SEASONALITY OF TWIN BIRTHS IN BRAZIL

The hypothesis of seasonality of twin births was investigated in two important maternity hospitals in the State of São Paulo, Brazil. The study included 1,386 twin births that occurred among 154,699 deliveries from 1984 to 1993. No evidence of seasonality has been detected either for the twin birth rate considered as a whole or for dizygotic twinning rate. The distributions of these rates fitted well sinusoidal regression curves but the cyclic trend did not correspond to any specific season.

Twin Pair Analysis of Some Palm Indexes

The heritability of two main line indexes (DLI and TLI), a palm crease index (API), and an ulnarity index (UI) were investigated by using twin pair methodology for quantitative traits. The analyses of the data allow to conclude that both DLI and API, which have been used to evaluate the obliquity of the main lines and the distal crease of the palm, should not be considered as depending upon an important genetic component. Otherwise, data on TLI and UI, while showing inconsistencies with the theoretical expectations, may be considered as genetic traits.