Evaluation of segregation ratio in Wilson's disease

Two problems relating to segregation analysis for Wilson's disease are discussed and a practical solution is presented. A problem in the ascertainment of families with Wilson's disease is illustrated by comparing segregation ratios calculated by the single selection, complete truncate, and multiple incomplete selection methods. The effect on the segregation ratio of exclusion from the analysis of those sibs who had died of other diseases at a young age is also discussed and a method of adjustment of the number of the affected using the data on age at onset is proposed. The segregation ratio by multiple incomplete selection (Weinberg proband method) after adjustment for those sibs who had died of other diseases was 0.243, consistent with the theoretical value for autosomal recessive inheritance. The segregation ratio calculated by the single selection method tended to give a lower value, while that calculated by the complete truncate method was greater than the theoretical value. Recessive inheritance is, however, supported. The actual effect of exclusion of those sibs who had died of other diseases on gene frequency estimation is shown to be very small.