Commingling and segregation analysis of blood pressure in consanguineous and nonconsanguineous families from Andhra Pradesh, India

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Abstract
The hypothesis of a major gene effect for systolic blood pressure (SBP) and diastolic blood pressure (DBP) was examined in families from Andhra Pradesh, India, where consanguinity and marriage within caste are commonly practiced. The data were examined separately by noninbred versus complete (inbred + noninbred) families, both before and after correction for residual skewness. For SBP in the noninbred sample prior to skewness transformation, evidence consistent with a relatively common major recessive gene (q = 0.31) accounted for approximately 30% of the variance. In the combined sample, although Mendelian τs were rejected, the major gene estimates were similar to those in the noninbred data, and failure to account for inbreeding in the likelihood function may have influenced the results. After transformation of the data for residual skewness only a multifactorial component resulted, which accounted for about 80% (complete sample) and 100% (noninbred sample) of the offspring variance, and less than 10% of the parental variance. Even though the major gene effect disappeared after skewness transformation, the putative recessive major gene found for SBP prior to the transformation may be genuine since the tests on the transmission probabilities supported Mendelian transmission while the equal τs hypothesis was rejected. For DBP, both a major nontransmissible effect accounting for about 20% of the variance and a multifactorial component accounting for about 55% (offspring) and about 15% (parents) was found. For the noninbred DBP data, transformation for residual skewness removed the major non‐Mendelian effect altogether. These data suggest inbreeding effects for SBP, with a pattern of smaller variances due to multifactorial sources (i.e., polygenic and/or cultural) in the sample which included consanguineous families. Adding inbred families reduced the evidence for Mendelian transmission of the major effect.