Holoprosencephaly in the west of Scotland 1975-1994.

Cases of holoprosencephaly which occurred in the west of Scotland over the past 20 years were ascertained from genetics, paediatric, and pathology department records. Fifty cases were identified of which 17 had an underlying cytogenetic abnormality. Of the remaining 33 cases, 26 were delivered after 28 weeks' gestation giving a birth prevalence of 1 in 26730. Twenty-one babies were liveborn and nine children are currently alive. All survivors are profoundly mentally retarded and most have seizures. Twenty-eight patients with non-chromosomal holoprosencephaly had a total of 23 sibs and three families were identified where there was either recurrence of holoprosencephaly (one family), a related cerebral malformation (one family), or mental handicap (one family) giving an overall recurrence risk for serious neurological disability of 12% (standard error 7%). We conclude that holoprosencephaly does not necessarily breed true and this observation should be taken into account when giving genetic counselling and attempting ultrasound prenatal diagnosis after the birth of an affected child.