Risk for reading disability as a function of parental history in three family studies

Inverse Bayesian analyses were applied to data from three large family studies of reading disability to estimate the posterior probability that an offspring will be affected, given that a parent reported a history of learning problems. Prior analyses presented elsewhere (Pennington et al., 1990), suggest that family transmission in these three studies is consistent with major gene or polygene influence. Posterior probability rates are presented in this paper for male to female sex ratios of 3.5:1 and 1:1, with population incidences estimated at 0.05 and 0.10. Results indicate that offspring risk rates are significantly elevated if a parent reports a history of RD. Specifically, an offspring's risk was increased 2 to 80 times over population expectancies when there was an affected parent. While the posterior probabilities and relative risk rates were fairly similar across studies, there was also some variation, which may reflect the different genetic mechanisms operating in these families. This study concludes that both absolute and relative risks are sufficiently increased in families with RD parents to warrant use of family history as a component in clinical evaluation. It is also evident from these results that consideration of the apparent mode of genetic transmission in families may provide even better information as to offspring risk, when family history is obtained.