β-Galactosidase deficiency in a Korat cat: a new form of feline G_M1-gangliosidosis

Abstract

A 7-month-old Korat cat was referred for a slowly progressive neurological disease. Circulating monocytes and lymphocytes showed the presence of single or multiple empty vacuoles and blood leukocytes enzyme assay revealed a very low β-galactosidase activity level (4.7 nmol/mg per h) as compared to unaffected parents and relatives. Histologically, the cat, euthanized at the owner request at 21 months of age, presented diffuse vacuolization and enlargement of neurons throughout the brain, spinal cord and peripheral ganglia, severe cerebellar neuronal cell loss, and moderate astrocytosis. Stored material was stained with periodic acid-Schiff on frozen sections and with the lectins Ricinus communis agglutinin-I, concanavalin A and wheat germ agglutinin on paraffin-embedded sections. Ultrastructurally, neuronal vacuoles were filled with concentrically whorled lamellae and small membrane-bound vesicles. In the affected cat, β-galactosidase activity was markedly reduced in brain (18.9%) and liver (33.25%), while total β-hexosaminidase activity showed a remarkable increase. Quantitation of total gangliosides revealed a 3-fold increase in brain and 1.7-fold in liver of affected cat. High-performance thin layer chromatography (HPTLC) detected a striking increase of G_M1-ganglioside. On densitometric analysis of HPTLC bands, the absorption of G_M1-ganglioside band was 98.52% of all stained bands (G_D1a ,G_D1b, G_T1b). Based on clinical onset, morphological and histochemical features, and biochemical findings, the Korat cat G_M1-gangliosidosis is comparable with the human type II (juvenile) form. However, clinical progression, survival time and level of β-galactosidase deficiency do not completely fit with those of human type II G_M1-gangliosidosis. The disease in the Korat cat is also different from other reported forms of feline G_M1-gangliosidosis.