Do familial neural tube defects breed true?

The tendency for sibs affected by non-syndromal neural tube defect (NTD) to have the same type of lesion was assessed retrospectively in a series of 66 affected sibships from the west of Scotland. Different schemes were used to classify the lesions: in the simplest classification into either anencephaly (including anencephaly-spina bifida) or spina bifida there was a tendency for spina bifida to breed true. More detailed description of the NTD in 48 sibships permitted classification according to location on the neuraxis; in this scheme sibs had dissimilar lesions. In 48 sets of affected sibs the lesions were separable into high NTD, which had involvement above vertebral level T12, and low NTD, which did not extend above T12. Low lesions comprised a minority of the total and each one occurred in a sibship with a high lesion. These results do not support the idea that NTDs occurring above and below vertebral level T12 have a different genetic basis.