USE OF ROBUST STATISTICAL-METHODS TO DETERMINE THE EFFECT OF FRAGILE-X ON MEANS AND VARIANCE-COMPONENTS OF A QUANTITATIVE TRAIT

Owing to the presence of outliers, an estimated 3.5% in the ridge brea dth data and 1.7% in the height data, the effect of fragile X on heigh t and ridge breadth was examined using robust statistical techniques f or data collected from 54 families afflicted with this disorder. It is shown that fragile X affects ridge breadth and height in a different manner. Fragile X women had a greater mean ridge breadth than normal w omen, whereas there was a similar trend, but no significant difference , between normal and fragile X men. Fragile X men were shorter than no rmal men, but no significant difference between the mean height of nor mal and fragile X women was observed. However, fragile X girls were sh own to grow more quickly and to stop growing earlier than normal girls . An examination of the covariance between relatives classified accord ing to fragile X status showed that for both traits the effect of frag ile X was to reduce the covariance between parents and offspring, whic h produced the effect of departure from an additive polygenic model of inheritance. (C) 1995 Wiley-Liss, Inc.