OBJECTIVE: To reevaluate previous claims that non-syndromic macrocephaly is usually inherited as an autosomal dominant trait. DESIGN: Head size was measured in the parents and sibs of children with non-syndromic macrocephaly. OUTCOME MEASURES: If autosomal dominant inheritance is involved, the frequency distribution should be bimodal. RESULTS: Head circumference of parents and sibs of the macrocephalic probands had a mean significantly greater than the population norm, and a unimodal distribution. Probands with psychomotor impairment had bigger heads, and more had a history of birth difficulty, than did unimpaired probands. CONCLUSIONS: The usual genetic basis for non-syndromic macrocephaly is multifactorial with a polygenic genetic basis, rather than autosomal dominant. Risk of recurrence appears to be much lower than if it would be on the assumption of autosomal dominant inheritance. Macrocephaly in a parent or sib of an unborn child may present a risk for birth injury to that child. A larger series of patients will be necessary to resolve this question.
OBJECTIVE: To reevaluate previous claims that non-syndromic macrocephaly is usually inherited as an autosomal dominant trait. DESIGN: Head size was measured in the parents and sibs of children with non-syndromic macrocephaly. OUTCOME MEASURES: If autosomal dominant inheritance is involved, the frequency distribution should be bimodal. RESULTS: Head circumference of parents and sibs of the macrocephalic probands had a mean significantly greater than the population norm, and a unimodal distribution. Probands with psychomotor impairment had bigger heads, and more had a history of birth difficulty, than did unimpaired probands. CONCLUSIONS: The usual genetic basis for non-syndromic macrocephaly is multifactorial with a polygenic genetic basis, rather than autosomal dominant. Risk of recurrence appears to be much lower than if it would be on the assumption of autosomal dominant inheritance. Macrocephaly in a parent or sib of an unborn child may present a risk for birth injury to that child. A larger series of patients will be necessary to resolve this question.