Summary

Galactosialidosis is a rare lysosomal storage disorder. There are three clinical phenotypes. The congenital or early infantile form is marked by edema, ascites, hepatosplenomegaly (it may appear as fetal hydrops), neurological disorders, kidney failure, facial dysmorphism, and skeletal and opthalmologic disorders (cherry-red spots and early blindness). The late infantile form is characterized by a normal or mildly affected mental state. The juvenile and adult forms (found mainly in Japan) are characterized by a slowly progressing neurological disorder, facial dysmorphism, dysostosis mutiplex, ophthamologic disorders (cherry-red spots and corneal opacities) and angiokeratomas. Galactosialidosis is caused by neuraminidase and beta-galactosidase deficiencies resulting from a primary deficiency in a third lysosomal protein: the bifunctional protein Protective Protein/Cathepsin A (PPCA). PPCA binds with beta-galactosidase and neuraminidase, forming a multienzymatic complex, and ensures their activity and stability within the lysosome. Transmission is autosomal recessive. The gene has been located on 20q13; it has been cloned and several mutations have been identified (one mutation accounts for the majority of the Japanese cases). Biological diagnosis is made by finding a characteristic chromatographic profile of urinary oligosaccharides. Results are confirmed by measuring the enzymatic activity of the alpha-D-neuraminidase and beta-galactosidase or carboxypeptidase A in fibroblasts, amniocytes, or the trophoblast. The only treatment is symptomatic.

Expert reviewer(s)

• Dr Roseline FROISSART
• Dr Irène MAIRE