GLA Activity Research Articles

Plasma globotriaosylsphingosine as a biomarker of Fabry disease

Fabry disease is an X-linked genetic disorder caused by a deficiency of α-galactosidase A (GLA) activity. As enzyme replacement therapy (ERT) involving recombinant GLAs has been introduced for this disease, a useful biomarker for diagnosis and monitoring of therapy has been strongly required. We measured globotriaosylsphingosine (lyso-Gb3) and globotriaosylceramide (Gb3) in plasma samples from ten hemizygous males (six classic and four variant cases) and eight heterozygous females with Fabry disease, and investigated the responses of plasma lyso-Gb3 and Gb3 in a male Fabry patient who had undergone ERT for 4 years to determine whether plasma lyso-Gb3 and Gb3 could be biomarkers of Fabry disease. The results revealed that plasma lyso-Gb3 was apparently increased in male patients and was higher in cases of the classic form than those of the variant one. In Fabry females, plasma lyso-Gb3 was moderately increased in both symptomatic and asymptomatic cases, and there was a correlation between the increase in lyso-Gb3 and the decrease in GLA activity. As to plasma Gb3, the levels in the variant Fabry hemizygotes and Fabry heterozygotes could not be distinguished from those in the controls, although those in the classic Fabry hemizygotes were increased. The plasma lyso-Gb3 level in the Fabry patient who had received ERT was elevated at the baseline and fell more dramatically on ERT than that of Gb3. Plasma lyso-Gb3 could thus be a potential biomarker of Fabry disease.

Newborn screening for Fabry disease by measuring GLA activity using tandem mass spectrometry

Fabry disease (FD) is an X-linked lysosomal storage disorder caused by the deficiency of alpha-galactosidase A (GLA). We evaluated a tandem mass spectrometry method to measure GLA activity. One 3.2mm punch from a dried blood spot sample (DBS) was incubated with substrate and internal standard in the reaction buffer for 22 h. The resulting product was quantified against internal standard using MS/MS. The median GLA activity of male newborn DBS (N=5025) was 9.85 + or - 6.4 micromol/h/l (CI 95% is 9.67-10.02 micromol/h/l); The median GLA activity of female newborns (N=4677) was 10.2 + or - 6.3 micromol/h/l (CI 95% is 10.02-10.38 micromol/h/l). The difference between the two subgroups is within assay analytical variation. The GLA activities in the DBS samples from 9 juvenile and adult males with previously identified FD were below 1.64 micromol/h/l. The GLA activities from 32 juvenile and adult females with confirmed FD were below 4.73 micromol/h/l. In 5 (16%) females GLA activities were above the 0.5th percentile of lower limit of CI 95% at 3.18 micromol/h/l. The MS/MS method for Fabry disease newborn screening is robust and can be readily multiplexed with other lysosomal disorders such as Pompe, Gaucher, Niemann-Pick, and Krabbe diseases.

Normal hearing in α-galactosidase A-deficient mice, the mouse model for Fabry disease

Fabry disease (OMIM 301500) is a rare X-linked recessive disorder caused by mutations in the α-galactosidase gene ( Gla). Loss of Gla activity leads to the abnormal accumulation of glycosphingolipids in lysosomes of predominantly vascular endothelial cells. Clinically the disorder presents with angiokeratomas, clouding of the cornea, and renal, cardiac, and cerebrovascular complications. In addition, there is an increased incidence of sensorineural hearing loss in Fabry patients. In this study, we investigated the loss of α-galactosidase A activity on hearing function in Gla-deficient mice ( Gla tm1Kul ). Gla mRNA was readily detected in the cochlea of 2- and 12-month old C57BL/6J and C3HeB/FeJ mice. The targeted allele was introgressed to the normal hearing C3HeB/FeJ strain to eliminate confounding genetic background effects. Auditory brain stem responses (ABR) to click, 8-, 16-, and 32 kHz stimuli measured at regular intervals from animals at the N4 backcross generation and from N4F1 hybrids demonstrated normal hearing in hemizygous and homozygous mutant mice up to 76 weeks of age. By histological criteria, the cyto-architecture of the mutant cochlea showed a normal appearance. The data demonstrate that in the mouse the loss of α-galactosidase A activity is genetically or biochemically buffered and not sufficient per se to cause an appreciable degree of hearing impairment.