Erythrocyte galactokinase assay with high performance liquid chromatography

Ultra fast and sensitive liquid chromatography tandem mass spectrometry based assay for galactose-1-phosphate uridylyltransferase and galactokinase deficiencies

The diagnosis of transferase and galactokinase deficiency galactosemia usually involves the measurement of erythrocyte galactose-1-phosphate uridylyltransferase (GALT) and galactokinase (GALK) enzyme activity, respectively. The current gold standard assays for these enzymes are radioactive assays, which are laborious and/or incapable of measuring low enzyme activities. To further our knowledge of genotype-phenotype relationships, we had developed an assay for GALT activity alone using LC-MS/MS. In this study we generated a robust and sensitive LC-MS/MS based GALT and GALK assay using a novel normal phase chromatographic condition. We improved upon our earlier assay by drastically reducing the instrument run time and eliminating the use of an ion pairing reagent. Stable isotope labeled substrates were utilized in the GALT and GALK assays. The enzymatic products ([(13)C(6)]-uridine diphosphate galactose in GALT assay and [(13)C(6)]-galactose-1-phosphate in GALK assay) were quantified in a 3 min LC-MS/MS run. The assays were sensitive enough to allow for the quantification of enzyme activities as low as 0.2% and 0.3% of normal control values in the GALT and GALK assays, respectively. Thirty-three samples from non-galactosemic patients were assayed to have erythrocyte GALT activity of 23.4±4.2 and GALK activity of 1.8±0.47 (mean±SD) μmol⋅(g Hgb)(-1) h(-1). Erythrocyte GALT activities in a cohort of 16 patients with classic or severe galactosemia were measured: 4 patients had GALT activity less than 1% of normal control values and the remaining 12 had no detectable GALT activity. No GALK activity was detected in a GALK deficient sample we analyzed. Lastly, we tested the feasibility of adapting this LC-MS/MS based GALT/GALK assay as a newborn screening (NBS) test.

Improvement of galactose uptake in Saccharomyces cerevisiae through overexpression of phosphoglucomutase: example of transcript analysis as a tool in inverse metabolic engineering

Through genome-wide transcript analysis of a reference strain and two recombinant Saccharomyces cerevisiae strains with different rates of galactose uptake, we obtained information about the global transcriptional response to metabolic engineering of the GAL gene regulatory network. One of the recombinant strains overexpressed the gene encoding the transcriptional activator Gal4, and in the other strain the genes encoding Gal80, Gal6, and Mig1, which are negative regulators of the GAL system, were deleted. Even though the galactose uptake rates were significantly different in the three strains, we surprisingly did not find any significant changes in the expression of the genes encoding the enzymes catalyzing the first steps of the pathway (i.e., the genes encoding Gal2, Gal1, Gal7, and Gal10). We did, however, find that PGM2, encoding the major isoenzyme of phosphoglucomutase, was slightly up-regulated in the two recombinant strains with higher galactose uptake rates. This indicated that PGM2 is a target for overexpression in terms of increasing the flux through the Leloir pathway, and through overexpression of PGM2 the galactose uptake rate could be increased by 70% compared to that of the reference strain. Based on our findings, we concluded that phosphoglucomutase plays a key role in controlling the flux through the Leloir pathway, probably due to increased conversion of glucose-1-phosphate to glucose-6-phosphate. This conclusion was supported by measurements of sugar phosphates, which showed that there were increased concentrations of glucose-6-phosphate, galactose-6-phosphate, and fructose-6-phosphate in the strain construct overexpressing PGM2.

Differential diagnosis of neonatal mild hypergalactosaemia detected by mass screening: clinical significance of portal vein imaging

The aetiology of hypergalactosaemia in 100 neonates detected by screening using the Paigen method is discussed. Hypergalactosaemia was transient in 94 cases and persistent in 6. The aetiology among transient cases was unknown in 55, delayed closure of the ductus venosus in 19, heterozygous UDP-galactose 4-epimerase (GALE) deficiency in 16, and heterozygous galactose-1-phosphate uridyltransferase (GALT) deficiency in 6. The aetiology among persistent cases was hepatic haemangioendothelioma with portovenous shunting in 2, and patent ductus venosus with hypoplasia of the intrahepatic portal vein, citrin deficiency, homozygous GALE deficiency, and heterozygous GALE deficiency in one patient each. The abnormalities of the portal system were identified ultrasonographically at the initial consultation and measurements of the total bile acid and alpha-fetoprotein concentrations were helpful in resolving the differential diagnosis. The causes of hypergalactosaemia varied, but a major cause was portosystemic shunt. Evaluation of patients with hypergalactosaemia should not be limited to enzymatic analysis, but should also include hepatic imaging, especially ultrasonography. Additionally, determination of total bile acids and alpha-fetoprotein is helpful in identifying the aetiology of hypergalactosaemia in infants.

Congenital porto-left renal venous shunt as a cause of galactosaemia

Congenital porto left renal venous (PRV) shunt was found to be the cause of galactosaemia in four galactosaemic neonates detected by mass screening (Paigen method). The patients did not have hereditary galactosaemias and were diagnosed as having galactosaemia of unknown cause, because porto-systemic venous (PS) shunts had not been recognized. At the time of diagnosis, hypergalactosaemia was not severe (0.44-0.55 mmol/L; 8-10 mg/dl) and plasma concentration of total bile acids (TBA) did not suggest a PS shunt (46-50 micromol/L). However, slightly but consistently increased concentrations of galactose and TBA strongly suggested the presence of a PS shunt, and careful ultrasonographic investigation revealed PRV shunt. We conclude that PRV shunt should be suspected in patients with hypergalactosaemia of unknown cause.

Delay of liver maturation as a cause of transient neonatal galactosemia

BACKGROUND

Because a large amount of serum alpha-fetoprotein (alpha-FP) is synthesized in the liver of the fetus or premature newborn, high concentrations or delayed degradation of serum alpha-FP during the neonatal period may reflect hepatic immaturity.

METHODS

In order to evaluate the relationship between transient neonatal galactosemia and delay of liver maturation, the concentration and half-life of serum alpha-FP during the neonatal period were measured in patients with transient galactosemia and in normal neonates.

RESULTS

No significant differences were observed in the serum concentration of alpha-FP between normal and galactosemic patients less than 1 month of age. However, the half-life of serum alpha-FP was significantly longer in galactosemic patients between 15 and 60 days of age compared with age-matched normal neonates.

CONCLUSION

Based on these results, we hypothesize that delay of liver maturation during the neonatal period, especially during the first 2 months after birth, can be a cause of transient neonatal galactosemia.