Ultrastructural studies as a method of prenatal diagnosis of neuronal ceroid-lipofuscinosis.

Ultrastructural studies of uncultured amniotic fluid cells obtained by genetic amniocentesis at 16 wk of gestation demonstrated 3 major cell types. Membrane bound curvilinear cytosomes were observed in about 30% of a subpopulation of dark, elongated cells. These are considered typical of the inclusions of the late infantile variant of neuronal ceroid-lipofuscinosis. This technique was used to monitor 6 at-risk pregnancies of which 2 were identified as affected. We have followed 6 of the 7 fetuses through to delivery with confirmation of our findings by skin biopsy in 4 and with clinical observations of a fifth child. There are major problems involved in the use of uncultured amniotic fluid cells for prenatal diagnosis. In addition to a great deal of heterogeneity of cell type, there is a considerable amount of tissue debris and a very high proportion of nonviable cells. We have examined chorionic villus tissues of 3 fetuses known to have inborn errors of lysosomal metabolism without finding any evidence of storage material. This is taken as an indication that the mutant gene(s) is not expressed in these tissues at this early stage of pregnancy. Notwithstanding these limitations, the usefulness of this technique in monitoring at-risk pregnancies has to be determined.