X-linked pattern of inheritance for serial measures of weight/stature.

The pattern of family resemblance for long-term serial measures of weight/stature (W/S ) in approximately 500 individuals from the Fels Longitudinal Growth Study suggests that X-linked genes may be contributing to the variability in this trait among children, particularly during the prepubertal age range of 2-9 years. In this data set, W/S was measured serially at the same ages in all family members. Thus, a parent-child correlation at a specific age can be determined even though the measurements were made on the child a generation later than on the parent. The pattern of family resemblance at each annual age up to 10 years and at ages 14-18 years is consistent with the presence of an X-linked genetic effect. Opposite-sex parent-child pairs are more similar than same-sex pairs, and sister-sister pairs are more similar than brother-brother or brother-sister pairs at these ages. Furthermore, when the distribution of W/S is examined separately in boys and girls, there is evidence of commingling in the distribution of boys from 5 to 8 years of age but not in girls. This is consistent with the existence of a major X-linked gene with a frequency of about 3%. This pattern of family resemblance and commingling suggestive of partial X-linkage for W/S has not been detected previously because cross-sectional family studies generally compare individuals at different stages of growth.