Severe child form of primary hyperoxaluria type 2 - a case report revealing consequence of GRHPR deficiency on metabolism

Abstract

BackgroundPrimary hyperoxaluria type 2 is a rare monogenic disorder inherited in an autosomal recessive pattern. It results from the absence of the enzyme glyoxylate reductase/hydroxypyruvate reductase (GRHPR). As a consequence of deficient enzyme activity, excessive amounts of oxalate and L-glycerate are excreted in the urine, and are a source for the formation of calcium oxalate stones that result in recurrent nephrolithiasis and less frequently nephrocalcinosis.Case presentationWe report a case of a 10-month-old patient diagnosed with urolithiasis. Screening of inborn errors of metabolism, including the performance of GC/MS urine organic acid profiling and HPLC amino acid profiling, showed abnormalities, which suggested deficiency of GRHPR enzyme. Additional metabolic disturbances observed in the patient led us to seek other genetic determinants and the elucidation of these findings. Besides the elevated excretion of 3-OH-butyrate, adipic acid, which are typical marks of ketosis, other metabolites such as 3-aminoisobutyric acid, 3-hydroxyisobutyric acid, 3-hydroxypropionic acid and 2-ethyl-3-hydroxypropionic acids were observed in increased amounts in the urine. Direct sequencing of the GRHPR gene revealed novel mutation, described for the first time in this article c.454dup (p.Thr152Asnfs*39) in homozygous form. The frequent nucleotide variants were found in AGXT2 gene.ConclusionsThe study presents metabolomic and molecular-genetic findings in a patient with PH2. Mutation analysis broadens the allelic spectrum of the GRHPR gene to include a novel c.454dup mutation that causes the truncation of the GRHPR protein and loss of its two functional domains. We also evaluated whether nucleotide variants in the AGXT2 gene could influence the biochemical profile in PH2 and the overproduction of metabolites, especially in ketosis. We suppose that some metabolomic changes might be explained by the inhibition of the MMSADH enzyme by metabolites that increase as a consequence of GRHPR and AGXT2 enzyme deficiency. Several facts support an assumption that catabolic conditions in our patient could worsen the degree of hyperoxaluria and glyceric aciduria as a consequence of the elevated production of free amino acids and their intermediary products.

Intermittent fasting and probiotic yogurt consumption are associated with reduction of serum alpha-N-acetylgalactosaminidase and increased urinary excretion of lipophilic toxicants

“…Interpretation of initial elevated level of 2HIB is more complex. Thus, 2HIB is formed endogenously as a product of branched-chain amino acid degradation in patients with ketoacidosis [11]. However, 2HIB is also a metabolite of gasoline additives [12], and elevated levels of 2HIB can indicate exposure to environmental pollution, exposure that could be associated with activities such as running in urban environments.…”

Case report: intermittent fasting and probiotic yogurt consumption are associated with reduction of serum alpha-N-acetylgalactosaminidase and increased urinary excretion of lipophilic toxicants

“…Thus, 2HIB is formed endogenously as a product of branched-chain amino acid degradation in patients with ketoacidosis. (11) However, 2HIB is also a metabolite of gasoline additives (12) , and elevated levels of 2HIB can indicate exposure to environmental pollution, exposure that could be associated with activities such as running in urban environments. Since Dr. JB had no clinical or laboratory signs of ketoacidosis, we interpret the elevated levels of 2HIB as consequence of environmental exposure.…”

3‐Hydroxyisobutyrate dehydrogenase (HIBADH) deficiency—A novel disorder of valine metabolism

“…3HiBuria caused by homozygous missense mutations in the ALDH6A1 gene was described by Chambliss et al and Sass et al 3,10 Secondary inhibition of MMSDH due to an increase of certain metabolites was described in glyoxylate reductase/hydroxypyruvate reductase and AGXT2 enzyme deficiency. 11 HIBADH can be inhibited because of defects in the respiratory chain and thus cause 3HiBuria. If the respiratory chain is defective, a disturbed oxidation of NADH leads to an increased NADH/NAD + -ratio.…”