General and dietary oxalate restriction advice reduces urinary oxalate in the stone clinic setting.

BACKGROUND: Idiopathic hyperoxaluria is a risk factor for developing calcium oxalate nephrolithiasis. Dietary oxalate's effect on urinary oxalate is not well studied. The aim of this study is to assess the effect of advice focused on reducing dietary oxalate in a cohort of idiopathic hyperoxaluric patients. METHODS: Patients referred to the Groote Schuur Hospital Stone Clinic from 2015 to 2017 were considered eligible, if they were an idiopathic hyperoxaluric stone former, excreting > 40 mg/d of urinary oxalate on a pre-intervention 24-hour stone study urinalysis. Patients were asked to adhere to a diet sheet which included general stone prevention advice (low salt diet, increased fluid intake and moderate protein intake) and specific low oxalate diet advice. A post-intervention 24-hour urinalysis was performed at six weeks. RESULTS: Nineteen patients had hyperoxaluria (eight men and 11 women) with a mean age of 49 years (range 25-76 years). The mean BMI of the group was 28.4 kg/m2 (17.4-50). All patients had mean number of 1.9 range prior stone episodes (range 1-6 stone episodes). Fourteen (14/19) patients completed the study. The mean pre-dietary advice urinary oxalate was 53.2 mg/24 hours (n = 14), SD while the post-intervention was 29.6 mg/24 hours SD (p = 0.0002). Only 3/14 patients who completed the assessment failed to normalise their urinary oxalate on the diet. CONCLUSION: In the stone clinic setting, general advice of low salt diet, increased water intake, moderate protein intake and specific oxalate restriction can significantly reduce oxalate excretion in hyperoxaluric stone formers. Sustained reduction of oxalate excretion and longitudinal clinical benefit are worthy of study in larger cohorts.

Primary hyperoxaluria type 1, a too often missed diagnosis and potentially treatable cause of end-stage renal disease in adults: results of the Dutch cohort.

BACKGROUND: Primary hyperoxaluria Type 1, an inherited disorder with increased endogenous oxalate production, leads to the development of urolithiasis, nephrocalcinosis and end-stage renal disease (ESRD). Contrary to the general belief that patients diagnosed during adulthood experience a relatively mild course of disease, we were confronted with several cases of ESRD caused by previously undiagnosed primary hyperoxaluria. METHODS: To study renal and patient survival in relation with genotype, age at onset of disease and therapeutic delay, we performed a nationwide search among all Dutch nephrologists and paediatric nephrologists. RESULTS: Of the 79 included patients, 38% was diagnosed at an adult age. ESRD was present at the time of diagnosis in 26% of paediatric diagnosed patients versus 52% of adult-diagnosed patients (P = 0.021). Homozygosity for the pyridoxine-responsive p.Gly170Arg or p.Phe152Ile genotype was found in 26% of paediatric diagnosed patients versus 68% of adult-diagnosed patients (P < 0.001). Of homozygous p.Gly170Arg or p.Phe152Ile patients, 48% developed ESRD at a median age of 37 years, compared with 48% in those with other mutations at a median age of 0.5 years (P < 0.001). Of the 16 patients found through family screening, 81% had a preserved renal function. CONCLUSIONS: The high prevalence of pyridoxine-responsive genotypes and favourably prognosis of timely treatment warrant early diagnostic screening for primary hyperoxaluria Type 1 in patients with recurrent urolithiasis. This will preserve kidney function and prevent diagnosis of adult diagnosed patients in ESRD.

[From gene to disease; primary hyperoxaluria type I caused by mutations in the AGXT gene]. / Van gen naar ziekte; primaire hyperoxalurie type I door mutaties in het AGXT-gen.

Primary hyperoxaluria type I (PH1) is a congenital defect in glyoxylate metabolism caused by a deficiency in the liver-specific peroxisomal enzyme known as alanine glyoxylate aminotransferase (AGT). The deficiency is due to mutations in the AGXT gene, located on chromosome 2q37.3, and results in the conversion of glyoxylate to oxalate. The crystallisation of oxalate with calcium results in symptoms varying from a solitary kidney stone to end-stage renal disease with systemic oxalosis. The diagnosis is based on increased oxalate and glycolate excretion in the urine, reduced AGT activity in liver tissue, and confirmed mutations in the AGXT gene. Over 50 disease-causing mutations have been identified in PH1, which are associated with a wide range of effects on the AGT enzyme. Homozygous Gly170Arg or Phei52Ile mutations are associated with a reduction in urinary oxalate excretion upon pyridoxine administration and long-term preservation of renal function when treatment is initiated in a timely manner. Homozygous 33insC and Gly82Arg mutations result in a much poorer prognosis. Mutational analysis of the AGXT gene in PH1 patients can be a useful tool for establishing the diagnosis and choosing an appropriate therapeutic strategy.

The 625G>A SCAD gene variant is common but not associated with increased C4-carnitine in newborn blood spots.

The 625G>A variant of the short-chain acyl-CoA dehydrogenase (SCAD) gene is considered to confer susceptibility for developing 'clinical SCAD deficiency' and appears to be common in the general population. To determine the frequency of the 625G>A variant in The Netherlands, we analysed 1036 screening cards of 5- to 8-day-old newborns and found 5.5% homozygous and 31.3% heterozygous for the 625G>A variant. An increased blood/plasma C4-carnitine concentration is considered to be one of the biochemical characteristics of SCAD deficiency. To explore the correlation of C4-carnitine levels with the 625G>A variant, we determined the C4-carnitine concentration, as well as the ratio of C4- to free carnitine, in blood spots from newborns, who were detected as homozygous, heterozygous or noncarriers for the gene variant. No significant differences were found between these groups. Our study demonstrates a high frequency of the 625G>A SCAD gene variant in the Dutch population, but no correlation to significantly increased C4-carnitine levels in blood spots taken between the 5th and 8th days of life. This latter observation might be the result of the relatively late timing of neonatal screening in our country, implying that fatty acid oxidation disorders may be missed at that stage. If the 625G>A variant is associated with clinical SCAD deficiency, the high frequency of the variant suggests a possible involvement of SCAD deficiency in the pathogenesis of common disorders, probably in relation to other genetic and/or environmental factors. However, homozygosity for the 625G>A variant might be only a biochemical phenomenon, representing a 'nondisease'.