Brain function in classic galactosemia, a galactosemia network (GalNet) members review

Classic galactosemia (CG, OMIM #230400, ORPHA: 79,239) is a hereditary disorder of galactose metabolism that, despite treatment with galactose restriction, affects brain function in 85% of the patients. Problems with cognitive function, neuropsychological/social emotional difficulties, neurological symptoms, and abnormalities in neuroimaging and electrophysiological assessments are frequently reported in this group of patients, with an enormous individual variability. In this review, we describe the role of impaired galactose metabolism on brain dysfunction based on state of the art knowledge. Several proposed disease mechanisms are discussed, as well as the time of damage and potential treatment options. Furthermore, we combine data from longitudinal, cross-sectional and retrospective studies with the observations of specialist teams treating this disease to depict the brain disease course over time. Based on current data and insights, the majority of patients do not exhibit cognitive decline. A subset of patients, often with early onset cerebral and cerebellar volume loss, can nevertheless experience neurological worsening. While a large number of patients with CG suffer from anxiety and depression, the increased complaints about memory loss, anxiety and depression at an older age are likely multifactorial in origin.

Dihydrolipoamide dehydrogenase, pyruvate oxidation, and acetylation-dependent mechanisms intersecting drug iatrogenesis

In human metabolism, pyruvate dehydrogenase complex (PDC) is one of the most intricate and large multimeric protein systems representing a central hub for cellular homeostasis. The worldwide used antiepileptic drug valproic acid (VPA) may potentially induce teratogenicity or a mild to severe hepatic toxicity, where the underlying mechanisms are not completely understood. This work aims to clarify the mechanisms that intersect VPA-related iatrogenic effects to PDC-associated dihydrolipoamide dehydrogenase (DLD; E3) activity. DLD is also a key enzyme of α-ketoglutarate dehydrogenase, branched-chain α-keto acid dehydrogenase, α-ketoadipate dehydrogenase, and the glycine decarboxylase complexes. The molecular effects of VPA will be reviewed underlining the data that sustain a potential interaction with DLD. The drug-associated effects on lipoic acid-related complexes activity may induce alterations on the flux of metabolites through tricarboxylic acid cycle, branched-chain amino acid oxidation, glycine metabolism and other cellular acetyl-CoA-connected reactions. The biotransformation of VPA involves its complete β-oxidation in mitochondria causing an imbalance on energy homeostasis. The drug consequences as histone deacetylase inhibitor and thus gene expression modulator have also been recognized. The mitochondrial localization of PDC is unequivocal, but its presence and function in the nucleus were also demonstrated, generating acetyl-CoA, crucial for histone acetylation. Bridging metabolism and epigenetics, this review gathers the evidence of VPA-induced interference with DLD or PDC functions, mainly in animal and cellular models, and highlights the uncharted in human. The consequences of this interaction may have significant impact either in mitochondrial or in nuclear acetyl-CoA-dependent processes.

Galactokinase deficiency: lessons from the GalNet registry

PURPOSE

Galactokinase (GALK1) deficiency is a rare hereditary galactose metabolism disorder. Beyond cataract, the phenotypic spectrum is questionable. Data from affected patients included in the Galactosemias Network registry were collected to better characterize the phenotype.

METHODS

Observational study collecting medical data of 53 not previously reported GALK1 deficient patients from 17 centers in 11 countries from December 2014 to April 2020.

RESULTS

Neonatal or childhood cataract was reported in 15 and 4 patients respectively. The occurrence of neonatal hypoglycemia and infection were comparable with the general population, whereas bleeding diathesis (8.1% versus 2.17-5.9%) and encephalopathy (3.9% versus 0.3%) were reported more often. Elevated transaminases were seen in 25.5%. Cognitive delay was reported in 5 patients. Urinary galactitol was elevated in all patients at diagnosis; five showed unexpected Gal-1-P increase. Most patients showed enzyme activities ≤1%. Eleven different genotypes were described, including six unpublished variants. The majority was homozygous for NM_000154.1:c.82C>A (p.Pro28Thr). Thirty-five patients were diagnosed following newborn screening, which was clearly beneficial.

CONCLUSION

The phenotype of GALK1 deficiency may include neonatal elevation of transaminases, bleeding diathesis, and encephalopathy in addition to cataract. Potential complications beyond the neonatal period are not systematically surveyed and a better delineation is needed.

The natural history of classic galactosemia: lessons from the GalNet registry

BACKGROUND

Classic galactosemia is a rare inborn error of carbohydrate metabolism, caused by a severe deficiency of the enzyme galactose-1-phosphate uridylyltransferase (GALT). A galactose-restricted diet has proven to be very effective to treat the neonatal life-threatening manifestations and has been the cornerstone of treatment for this severe disease. However, burdensome complications occur despite a lifelong diet. For rare diseases, a patient disease specific registry is fundamental to monitor the lifespan pathology and to evaluate the safety and efficacy of potential therapies. In 2014, the international Galactosemias Network (GalNet) developed a web-based patient registry for this disease, the GalNet Registry. The aim was to delineate the natural history of classic galactosemia based on a large dataset of patients.

METHODS

Observational data derived from 15 countries and 32 centers including 509 patients were acquired between December 2014 and July 2018.

RESULTS

Most affected patients experienced neonatal manifestations (79.8%) and despite following a diet developed brain impairments (85.0%), primary ovarian insufficiency (79.7%) and a diminished bone mineral density (26.5%). Newborn screening, age at onset of dietary treatment, strictness of the galactose-restricted diet, p.Gln188Arg mutation and GALT enzyme activity influenced the clinical picture. Detection by newborn screening and commencement of diet in the first week of life were associated with a more favorable outcome. A homozygous p.Gln188Arg mutation, GALT enzyme activity of ≤ 1% and strict galactose restriction were associated with a less favorable outcome.

CONCLUSION

This study describes the natural history of classic galactosemia based on the hitherto largest data set.