Primary hyperoxaluria type 1 with a novel mutation

Case series and literature review of primary hyperoxaluria type 1 in Chinese patients

Based on the single-center case reports and all reported patients with primary hyperoxaluria type 1 (PH1) in China, this study discussed the clinical and genetic characteristics of this disease retrospectively. We reported and validated a novel genetic variation c.302 T > G: the clinical phenotypes of the two siblings were similar, in which both had onset in infancy, mainly manifested as renal insufficiency, and died within 6 months out of end-stage renal disease. The literature review is the first to summarize the Chinese patients with PH1 up to now. Forty-eight Chinese patients were included, containing 7 adults and 41 children. The median onset age was 51 months, and the ratio of male to female was 2.69:1. It showed a poor prognosis: 51.1% of Chinese primary hyperoxaluria type 1 patients suffered from end-stage renal disease, and 38.9% of patients died. Urolithiasis was the most common clinical manifestation both in adults and children, while infant-onset patients generally presented with renal insufficiency and had a higher mortality of 75.0%. One hundred and forty-nine AGXT mutant alleles are currently known in the Chinese population, c.33dupC and c.815_816insGA were the most common AGXT genes, accounting for 12.0% and 10.1% of allele frequencies, respectively. The exons 1, 2, 6, and 8 were the most common locations of gene variants, accounting for 78% of all variants, which will be promising targets of DNA sequencing for primary hyperoxaluria type 1.

Primary hyperoxaluria: a case series

BACKGROUND

Primary hyperoxaluria (PH) is a rare genetic disorder characterized by the excessive production and accumulation of oxalate. We present five cases of PH, each exhibiting varying manifestations of the disorder including a case presenting as postpartum kidney failure. Notably, three of these cases involve a previously unreported mutation.

CASE PRESENTATIONS

We evaluated five Indian patients who presented with varying manifestations of PH. The first case, a 30 year old woman, presented as post-partum kidney failure and was found to be having oxalate nephropathy precipitated by dietary oxalate overload in the setting of previously undiagnosed PH. Genetic analysis revealed a previously unreported mutation in the alanine-glyoxylate aminotransferase gene. The patient underwent simultaneous kidney liver transplant. The second and third cases, 26 and 28 year old women respectively, were asymptomatic siblings of the first patient, who were diagnosed through screening. The fourth case is a 12 year boy with PH type 1 presenting as nephrolithiasis and rapidly worsening kidney function requiring combined kidney liver kidney transplant. Case 5 is a 6 year old male child with type 2 PH presenting with nephrolithiasis, nephrocalcinosis and normal kidney function. All the patients were born to consanguineous parents.

CONCLUSIONS

Due to limited clinical suspicion and inadequate diagnostic resources in certain countries with limited resources, it is possible for PH to go undiagnosed. The manifestations of the disease can range from no noticeable symptoms to severe disease. Interestingly, in some individuals with primary hyperoxaluria, the disease may not exhibit any symptoms until it is triggered by a high intake of dietary oxalate.

Metabolism of Oxalate in Humans: A Potential Role Kynurenine Aminotransferase/Glutamine Transaminase/Cysteine Conjugate Beta-lyase Plays in Hyperoxaluria

Hyperoxaluria, excessive urinary oxalate excretion, is a significant health problem worldwide. Disrupted oxalate metabolism has been implicated in hyperoxaluria and accordingly, an enzymatic disturbance in oxalate biosynthesis can result in the primary hyperoxaluria. Alanine glyoxylate aminotransferase-1 and glyoxylate reductase, the enzymes involving glyoxylate (precursor for oxalate) metabolism, have been related to primary hyperoxalurias. Some studies suggest that other enzymes such as glycolate oxidase and alanine glyoxylate aminotransferase-2 might be associated with primary hyperoxaluria as well, but evidence of a definitive link is not strong between the clinical cases and gene mutations. There are still some idiopathic hyperoxalurias, which require a further study for the etiologies. Some aminotransferases, particularly kynurenine aminotransferases, can convert glyoxylate to glycine. Based on biochemical and structural characteristics, expression level, subcellular localization of some aminotransferases, a number of them appear able to catalyze the transamination of glyoxylate to glycine more efficiently than alanine glyoxylate aminotransferase-1. The aim of this minireview is to explore other undermining causes of primary hyperoxaluria and stimulate research toward achieving a comprehensive understanding of underlying mechanisms leading to the disease. Herein, we reviewed all aminotransferases in the liver for their functions in glyoxylate metabolism. Particularly, kynurenine aminotransferase-I and III were carefully discussed regarding their biochemical and structural characteristics, cellular localization, and enzyme inhibition. Kynurenine aminotransferase-III is, so far, the most efficient putative mitochondrial enzyme to transaminate glyoxylate to glycine in mammalian livers, might be an interesting enzyme to look over in hyperoxaluria etiology of primary hyperoxaluria and should be carefully investigated for its involvement in oxalate metabolism.

Primary Hyperoxaluria Type 1 with Homozygosity for a Double-mutated AGXT Allele in a 2-year-old Child

Primary hyperoxaluria (PH) Type 1 is a rare, genetic disorder caused by deficiency of the liver enzyme alanine-glyoxylate aminotransferase, which is encoded by AGXT gene. We report a 2-year-old South Indian Tamil child with nephrocalcinosis due to PH Type 1, in whom a homozygous genotype for two missense mutations in the AGXT gene was found: first, a C to G transversion (c. 32C>G) in exon 1 resulting in the amino acid substitution p.Pro11Arg; second, a T to A transversion (c. 167T>A) in exon 2 resulting in p.Ile56Asn. A therapy based on potassium citrate and pyridoxine was started. This is the first report of molecular testing-proven childhood onset-PH Type 1 from South India and is notable for the co-occurrence of two missense mutations in one AGXT allele, which might lead to different and more severe phenotype than each mutation alone. To the best of our knowledge, AGXT allele carrying two already known mutations has not been previously reported.

Common mutation underlying primary hyperoxaluria type1 in three Indian children

Primary hyperoxaluria is an autosomal recessive disorder caused by deficiency of alanine-glyoxylate aminotransferase, which is encoded by the AGXT gene. We report three Indian children with primary hyperoxaluria type1 having a common mutation in this gene. All patients had evidence of chronic kidney disease at the time of diagnosis, with subsequent progression to end-stage renal disease. The detection of an identical mutation in the AGXT gene suggests that specific genetic screening for this mutation may be useful when considering the diagnosis of primary hyperoxaluria type1.