Aspartylglucosaminuria

An autosomal recessive lysosomal storage disease belonging to the oligosaccharidosis group (also called glycoproteinosis).

Epidemiology

Aspartylglucosaminuria (AGU) is only exceptionally found outside of Finland.

Clinical description

Clinical signs of AGU include slowly developping mental retardation, beginning with clumsiness, late speech, and hyperkinesia, mild facial dysmorphism, and slight kyphoscoliosis. Hepatosplenomegaly is rare and has only been reported in non-Finnish cases.

Etiology

AGU is caused by mutations in gene AGU located on 4q34.3. In Finland, two major mutations have been evidenced (AGUfin major and AGUfin minor) that account for 98% of diseased alleles, and systematic screening for heterozygous individuals has thus been made possible. Elsewhere, mutations are very heterogenous. Mutations lead to deficiency in N-aspartylglycosaminidase, an enzyme that cleaves N-acetylglycosamine-asparagine bond found into many glycopeptides and N-glycosyled proteins, and causes excess accumulation of glycoasparagine in the body tissues and its increased excretion in urine.

Diagnostic methods

Biochemically it is characterized by increased urinary excretion of aspartylglycosamine on an aminoacid or oligosaccharide chromatography. Results are confirmed by the low activity of aspartylglycosaminidase measured in lymphocytes, fibroblasts, amniocytes or the trophoblast.

Genetic counseling

Transmission is autosomal recessive

Management and treatment

The only attempt of curative treatment to this day is allogenic bone marrow grafting, but the results in 5 Finnish patients were limited.