The characteristics of the
sialidase (N-acetyl-alpha-
neuraminidase) of human leukocytes, fibroblasts and amniotic fluid cell cultures were determined with a radioactive assay method utilizing neuramin-[3H]
lactitol as the
enzyme substrate. Fibroblast cultures from patients with the inherited
sialidase deficiency diseases including
mucolipidosis I,
sialidosis I and
sialidosis II, juvenile type have less than 10% of normal
sialidase activity using either this substrate, 2-(3'-methoxyphenyl)-N-acetyl-alpha-neuraminic
acid, or 2'-(4-methylumbelliferyl)-N-acetyl-alpha-neuraminic
acid. The total
sialic acid content of fibroblasts and leukocytes from
mucolipidosis I and
sialidosis I patients is greatly elevated; this parameter is useful in establishing a diagnosis of
sialidase deficiency. The
sialic acid content of
sialidosis II, juvenile type, with coexistent
sialidase and
beta-galactosidase deficiencies, is only slightly elevated above normal levels. A patient with
mucolipidosis I has 16% of normal neuramin-[3H]
lactitol sialidase activity in his peripheral leukocytes. His parents were clearly distinguished from the normal range using leukocyte
enzyme levels and a maternal aunt was identified as a possible carrier. The presence of this
enzyme in amniotic fluid cell cultures, both fibroblastic and mixed cell type, makes possible the prenatal detection of these diseases. A pregnancy from a family at risk for having a child with
mucolipidosis I was monitored by amniocentesis and subsequent
sialidase measurement of the amniotic fluid cell cultures.