[3 recent cases of Noonan's syndrome].

In the present state of our knowledge of cytogenetics, it seems logical to distinguish Noonan's syndrome from Turner's syndrome, thanks to the following arguments: Althought there are minor differences in the morphotype, the small size and the mental retardation are the same in both cases. However there are two lines of evidence: The first, inconstant, concerns the lesser intensity of the gonad changes, especially in the female sex, explaining the relative frequency of the familial forms of the syndrome, of Noonan, which are then trasmitted as autosomic dominants with variable penetrance. The second, constant and formal until now, concern the chromosome abnormalities. Present in Turner's syndrome, which they help to define in both sexes, they are always absent in Noonan's syndrome, in boys as in girls.