Heritability of the somatotype components in Biscay families

The anthropometric somatotype is a quantitative description of body shape and composition. Familial studies indicate the existence of a familial resemblance for this phenotype and they suggest a substantial action by genetic factors on this aggregation.The aim of this study is to examine the degree of familial resemblance of the somatotype components and of a factor of shape, in a sample of Biscay nuclear families (Basque Country, Spain).One thousand three hundred and thirty nuclear families were analysed. The anthropometric somatotype components [Carter, J.E.L., Heath, B.H., 1990. Somatotyping. Development and applications. Cambridge University Press, Cambridge, p. 503] were computed. Each component was fitted for the other two through a stepwise multiple regression, and also fitted through the LMS method [Cole, T., 1988. Fitting smoothed centile curves to reference data. J. Roy. Stat. Soc. 151, 385–418] in order to eliminate the age, sex and generation effects. The three raw components were introduced in a PCA from which a shape factor (PC1) was extracted for each generation. The correlations analysis was performed with the SEGPATH package [Province, M.A., Rao, D.C., 1995. General purpose model and computer programme for combined segregation and path analysis (SEGPATH): automatically creating computer from symbolic language model specifications. Genet. Epidemiol. 12, 203–219]. A general model of transmission and nine reduced models were tested. Maximal heritability was estimated with the formula of [Rice, T., Warwick, D.E., Gagnon, J., Bouchard, C., Leon, A.S., Skinner, J.S., Wilmore, J.H., Rao, D.C., 1997. Familial resemblance for body composition measures: the HERITAGE family study. Obes. Res. 5, 557–562].The correlations were higher between offspring than in parents and offspring and a significant resemblance between mating partners existed. Maximum heritabilities were 55%, 52% and 46% for endomorphy, mesomorphy and ectomorphy, respectively, and 52% for PC1.In conclusion, the somatotype presents a moderate degree of familial aggregation. For the somatotype components, as well as for PC1, the degree of familial resemblance depends on age. The sex only has a significant effect on ectomorphy.

ResumenEl somatotipo antropométrico consiste en una descripción cuantitativa de la forma del cuerpo y de su composición. Los estudios familiares indican la existencia de un parecido familiar para este fenotipo y sugieren la acción de los factores genéticos en esta agregación.El objetivo de este estudio es examinar el grado de semejanza familiar de las componentes del somatotipo en una muestra de familias nucleares de Vizcaya (País Vasco).Se analizaron 1.330 familias nucleares. Se calcularon las componentes del somatotipo antropométrico (Cartery Heath, 1990). Cada componente se ajustó para los efectos de las otras dos mediante una regresión múltiple “stepwise” y para eliminar los efectos de la edad, sexo y generación, se ajustaron mediante el método LMS (Cole, 1988). Las componentes sin ajustar se introdujeron en un ACP del que se obtuvo un factor de forma (PC1) en cada generación. Las correlaciones se estimaron con el programa SEGPATH (Provincey Rao, 1995). Se probaron un modelo general de transmisión y nueve modelos reducidos. La heredabilidad máxima se estimó mediante la formula de Rice et al. (1997).Las correlaciones fueron más elevadas entre los descendientes que con sus progenitores, y se detectó un parecido significativo entre los esposos. Las heredabilidades máximas fueron 55%, 52% y 46% para la endomorfia, mesomorfia y ectomorfia, respectivamente, y 52% para el PC1.En conclusión, el somatotipo presenta un grado moderado de agregación familiar. La semejanza familiar de las componentes y del PC1 depende de la edad. El sexo tiene un efecto significativo sobre la ectomorfia.