In patient SK-1 nephrolithiasis was likely to be due to multiple risk factors including renal wasting of urate, episodes of cyclic vomiting leading to concentrated urine and hypocitraturia. In patient SK-4, who also had a molecular genetic diagnosis of Alport syndrome, attacks of gross hematuria were confusing due to presence of colicky pain and eumorphic red blood cells, which are not usual features of Alport syndrome. In this patient, we found the mutation p.R347S. Cheong et al. reported a similar case to this, where a 14 year old girl who presented with acute post-streptococcal glomerulonephritis. Although her nephritis had a favorable course, the microhematuria persisted more than one year. On reevaluation this girl was found to have low serum uric acid with increased Kinase Inhibitor Library molecular weight FEurate in favor of idiopathic hypouricaemia. Mutational analysis in this patient revealed heterozygous W258X mutation in SLC22A12. Patient SK-2 has hypertension and moderate proteinuria due to reflux nephropathy, presumably as a coincidental finding to the functionally significant p.R434H variant. As hypertension in the context of renal disease is often treated with ACE inhibitors or angiotensin receptor antagonists, some caution is advisable. Both losartan and irbesartan have an inhibitory action on URAT1. Thus treatment with these agents has potential to have a marked uricosuric effect in patients with homozygous URAT1 mutations. Patient SK-3 had a complex phenotype of distal renal tubular acidosis and renal hypouricaemia, associated with the p.R434C mutation within URAT1. It is well known that hypouricaemia may be associated with distal renal tubular acidosis at diagnosis as a part of transitory proximal tubular dysfunction. In additional, pharmacological agents may also disrupt proximal tubular handing of urate. In our case, hypouricaemia persisted for more than 2 years despite a normalization of other proximal tubular functions. Definitively, mutational analysis of SLC22A12 with a functionally significant change explained the persistent hypouricaemia in this patient. Patient NC-1 was a recurrent calcium stone former, with a past medical history of type 1 diabetes. Here, serum urate levels were only borderline low and the FEurate was also only transiently raised at 16%. The missense mutation p.V388M was associated with negative functional data, with no significant change in urate transport in HEK293 cell experiments. Inclusion of this case is helpful as the negative functional data and the transient hypouricaemia are consistent with this variant being benign. The dataset derived from the V388M variant allow a comparison to be made between it and the more functionally significant variants, acting as another negative control. Given the hypouricaemia was transient in this case, we do not assume that this sequence variant is causative. From our sequence variants of URAT1, mutations with an impact upon uric acid handling are associated with a persistent hypouricaemia. Patient NC-2 was also a recurrent stone former, with persistently low serum uric acid. The heterozygous missense mutation, p.I75T was confirmed to be functionally significant in HEK293 urate uptake studies. In previously reported Japanese and Korean cases of idiopathic renal hypouricaemia secondary to SLC22A12 mutations.