Sialidoses, new types of inborn diseases.

While mucolipidosis I and its variants are well defined as sialidosis, the basic defect in mucolipidosis II and III is still discussed. The neuraminidase defect in these disorders is generally considered as one of many lysosomal hydrolase deficiencies, accompanied by a high extracellular activity of these enzymes. Our hypothesis of a specific alpha-neuraminidase defect, in these cases, is based on the fact that it is common to numerous tissues and extracellular fluids, in opposite to other hydrolases activities. The choice of the substrate for the alpha-neuraminidase determination appears to be very important, in view of their peculiar specificities.