What is the incidence of holoprosencephaly?

The incidence of holoprosencephaly with normal chromosomes has been estimated at between 1 in 16 000 and 1 in 53 394 live births. It has been found that during a 3-year period in the Bristol and Weston Health District there were six cases of holoprosencephaly, two of which were familial, and these cases are described. This represents an incidence of 1 in 5200 and during the preceding 3-year period the incidence in the same area was 1 in 14 520 births.