Megalencephaly familial
Incidence
Inheritance: Male-limited autosomal dominant The usual genetic basis for nonsyndromic macrocephaly is multifactorial with a polymorphic genetic basis, rather than autosomal dominant.
Clinical Characteristics
Arbour et al. (1996) addressed the question of the proper interpretation of nonsyndromic macrocephaly with psychomotor impairment. The problem is particularly difficult if a parent also has macrocephaly without psychomotor impairment. Possible interpretations include that the associations are coincidental, that the macrocephaly results from a genetically determined abnormality of the cerebral architecture that might also lead to psychomotor delay, or that the macrocephaly had a genetic basis and the delay was a secondary result of the birth process on the big head. Head size was measured in the parents and sibs of 23 patients with a head circumference more than 2 SD above the mean and with no evidence of hydrocephalus or syndromic associations. In 12 of the 23, some degree of psychomotor impairment was present. It was found that head circumference of parents and sibs 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. Arbour et al. (1996) concluded that the usual genetic basis for nonsyndromic macrocephaly is multifactorial with a polymorphic genetic basis, rather than autosomal dominant. A risk of recurrence appeared to be much more lower than 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. The following signs are seen very frequently: broad nose, short neck, macrocephaly, pointed chin, frontal bossing, truncal obesity, delayed bone age, large fontanelle, prominent occiput, dolicho/scaphocephaly, deepset eyes/enophthalmos, autosomal dominant inheritance, mental retardation(degree not assessed). These signs are frequenly seen: genu valgum, macropenis/large penis, auricular septal defect, macroorchidism/macrotestes.
Precipitants
none
Provocation Tests
none
Diagnostic Procedures
It is a clinical diagnosis