Disorders of galactose, pentose, and pyruvate metabolism

Inborn errors of galactose metabolism—galactose is principally found as free lactose in dairy products. Three inborn errors of galactose metabolism are recognized: (1) galactokinase deficiency (‘galactose diabetes’)—a very rare condition which impairs the assimilation of dietary galactose such that the free sugar and its metabolites appear in plasma and urine; (2) classical galactosaemia (galactose-1-phosphate uridylyltransferase deficiency)—the commonest (1/47 000 births) and most important disorder. High concentrations of galactose in the plasma and tissues lead to aberrant glycosylation of glycoproteins and other glycoconjugates, including lipids. The principal manifestations are a bactericidal defect associated with neonatal Escherichia coli sepsis; failure to thrive; and—in older patients—growth retardation, mental retardation, renal Fanconi’s syndrome, jaundice, and hepatosplenomegaly: without exclusion of lactose and galactose, death with cirrhosis is the rule. (3) Uridine diphosphate galactose-4´-epimerase deficiency—a rare but often harmless disorder which may be identified by neonatal screening. Rarely, cataract, sensorineural deafness and impaired psychomotor development with hepatorenal features of classical galactosaemia occur, with favourable responses to the galactose exclusion diet. Pentosuria—essential pentosuria is an asymptomatic, autosomal recessive trait affecting glucuronate metabolism, principally found in Ashkenazi Jews. Disorders of pyruvate metabolism—deficiency of the pyruvate dehydrogenase complex is the most common inherited disorder with lactic acidaemia, most often due to deficiency of the E1α‎ subunit inherited as a dominant X-linked character. Presentation is with overwhelming neonatal acidosis; moderate lactic acidosis with progressive neurological features; or—in male children and young adults—an indolent neurological course without overt acidosis but with episodes of cerebellar ataxia induced by carbohydrate administration. Pyruvate carboxylase deficiency causes lactate/pyruvate acidosis with a necrotizing encephalopathy resembling Wernicke’s encephalopathy. Hypoglycaemia may complicate intercurrent infections and starvation.

Insights into the Pathophysiology of Infertility in Females with Classical Galactosaemia

Classical galactosaemia (CG) (OMIM 230400) is a rare inborn error of galactose metabolism caused by the deficiency of the enzyme galactose-1-phosphate uridylyltransferase (GALT, EC 2.7.7.12). Primary ovarian insufficiency (POI) is the most common long-term complication experienced by females with CG, presenting with hypergonadotrophic hypoestrogenic infertility affecting at least 80% of females despite new-born screening and lifelong galactose dietary restriction. In this review, we describe the hypothesized pathophysiology of POI from CG, implications of timing of the ovarian dysfunction, and the new horizons and future prospects for treatments and fertility preservation.

Including Classical Galactosaemia in the Expanded Newborn Screening Panel Using Tandem Mass Spectrometry for Galactose-1-Phosphate

Galactosaemia has been included in various newborn screening programs since 1963. Several methods are used for screening; however, the predominant methods used today are based on the determination of either galactose-1-phosphate uridyltransferase (GALT) activity or the concentration of total galactose. These methods cannot be multiplexed and therefore require one full punch per sample. Since the introduction of mass spectrometry in newborn screening, many diseases have been included in newborn screening programs. Here, we present a method for including classical galactosaemia in an expanded newborn screening panel based on the specific determination of galactose-1-phosphate by tandem mass spectrometry. The existing workflow only needs minor adjustments, and it can be run on the tandem mass spectrometers in routine use. Furthermore, compared to the currently used methods, this novel method has a superior screening performance, producing significantly fewer false positive results. We present data from 5500 routine newborn screening samples from the Danish Neonatal Screening Biobank. The cohort was enriched by including 14 confirmed galactosaemia positive samples and 10 samples positive for other metabolic disorders diagnosed through the Danish newborn screening program. All galactosaemia positive samples were identified by the method with no false positives. Furthermore, the screening performance for other metabolic disorders was unaffected.

Validation of an automated ultraperformance liquid chromatography IgG N-glycan analytical method applicable to classical galactosaemia

Background Classical galactosaemia (OMIM #230400) is a rare disorder of carbohydrate metabolism caused by deficiency of the galactose-1-phosphate uridyltransferase enzyme. The pathophysiology of the long-term complications, mainly cognitive, neurological and female fertility problems, remains poorly understood. Current clinical methods of biochemical monitoring lack precision and individualization with an identified need for improved biomarkers for this condition. Methods We report the development and detailed validation of an automated ultraperformance liquid chromatography N-glycan analytical method of high peak resolution applied to galactose incorporation into human serum IgG. Samples are prepared on 96-well plates and the workflow features rapid glycoprotein denaturation, enzymatic glycan release, glycan purification on solid-supported hydrazide, fluorescent labelling and post-labelling clean-up with solid-phase extraction. Results This method is shown to be accurate and precise with repeatability (cumulative coefficients of variation) of 2.0 and 8.5%, respectively, for G0/G1 and G0/G2 ratios. Both serum and processed N-glycan samples were found to be stable at room temperature and in freeze–thaw experiments. Conclusions This high-throughput method of IgG galactose incorporation is robust, affordable and simple. This method is validated with the potential to apply as a biomarker for treatment outcomes for galactosaemia.