MO048PATHOGENIC VARIANTS IN CHLORIDE VOLTAGE-GATED CHANNEL 5 (CLCN5), ASSOCIATED WITH DENT DISEASE TYPE 1, SHOULD BE CONSIDERED IN END-STAGE KIDNEY DISEASE OF UNKNOWN AETIOLOGY
Authors: Leggatt Gary , Gast Christine , Gilbert Rodney , Veighey Kristin , Rahman Tahmina , Ennis Sarah 
Published: May 2021

Abstract

Background and Aims
Hemizygous variants in chloride voltage-gated channel 5 (CLCN5) on chromosome Xp11.22 cause Dent disease type 1, characterised by low-molecular-weight proteinuria, hypercalciuria, nephrocalcinosis, nephrolithiasis, and progressive renal failure. We describe a truncating pathogenic variant in two brothers presenting with end-stage kidney disease (ESKD) and no evidence of nephrolithiasis or nephrocalcinosis.

Method
Two white British brothers presented to a different regional centre over 20 years ago with ESKD of unknown aetiology. The UK 100,000 Genomes Project provided a unique opportunity to make a molecular diagnosis using whole-genome sequencing linked to clinical records.

Results
The older brother presented with ESKD aged 23 with bilateral small kidneys and no evidence of nephrolithiasis or nephrocalcinosis on ultrasound. He had various musculoskeletal pains, 'cutaneous ectopic calcification' and secondary hyperparathyroidism, all of which improved post parathyroidectomy. Investigation of his 17-year-old brother for consideration of kidney transplant donation revealed progressive chronic kidney disease (CKD), microscopic haematuria, proteinuria (3g/24hours) and hypokalaemia. There was no nephrocalcinosis or renal calculi on ultrasound or cystoscopy. Renal biopsy showed tubulointerstitial changes with patchy fibrosis and marked chronic inflammatory cell infiltrates. He had a history of enuresis, polydipsia, delayed bone age and general developmental delay. ESKD by the age of 22 was complicated by hypertension and hyperparathyroidism requiring parathyroidectomy. Right knee pain with 'unusual osteochondral abnormality' on MRI resulted in a supracondylar femoral osteotomy. Early serum and urine biochemistry results were not available. A hemizygous nonsense variant p.Arg417Ter in CLCN5 was identified by whole-genome sequencing via the 100,000 Genomes Project. Sanger sequencing at the Wessex Regional Genetics Laboratory confirmed this. This variant was predicted to be protein-truncating, was absent in the genome aggregation database (gnomAD) and equivalent to a variant associated with Dent disease in other patients therefore classified as a class 5 pathogenic variant according to ACMG guidelines. Three male children with Dent disease have previously been reported with the pathogenic variant p.Arg347Ter. A seven and a twelve year old from two different families in Japan had microscopic haematuria, proteinuria, elevated β2-microglobulin and normal renal function. The twelve-year-old had mild hypercalciuria, but neither had a history of nephrolithiasis or nephrocalcinosis. A four-year-old Turkish boy manifested hypophosphataemia, nephrolithiasis and nephrocalcinosis. Unusually for Dent disease, he also had hypokalaemic hypochloraemic metabolic alkalosis and hyper-reninaemic hyperaldosteronism more characteristic of Bartter syndrome, but with elevated β2-microglobulin more typical of Dent disease. None of these cases had CKD but were all reported at a very young age.

Conclusion
Approximately 15% of patients with ESKD in Europe have an unknown aetiology. Dent disease has a variable phenotype and screening of patients for low molecular weight proteinuria such as β2-microglobulin is not routinely performed. Dent disease type 1 should be considered in patients presenting with unexplained renal failure even without typical clinical features.