Kidney stones are common and can arise from many etiologies including genetic and environmental. Biallelic pathogenic variants in the solute carrier family 34-member 3 (SLC34A3) gene cause Hereditary Hypophosphatemic Rickets with Hypercalciuria (HHRH), while both monallaelic and biallelic pathogenic variants in SLC3A1 cause cystinuria. Here, we report the clinical phenotype of a patient with concomitant biallelic and monoallelic pathogenic variants in SLC34A3 and SLC3A1 respectively.

Renal phosphate transporters NaPi-IIa (SLC34A1) and NaPi-IIc (SLC34A3) play a crucial role in phosphate reabsorption in the proximal tubule. Biallelic loss-of-function variants in SLC34A1 and SLC34A3 cause two rare phosphate-wasting tubulopathies: idiopathic infantile hypercalcemia (IIH) and hereditary hypophosphatemic rickets with hypercalciuria, respectively. The phenotypes associated with these diseases are highly variable and sometimes overlap. Here, we report a rare case of a six-month-old girl of consanguineous parents with symptoms related to these diseases, including failure to thrive, nephrocalcinosis, hypercalcemia, hypophosphatemia with low TRP, elevated levels of 1,25-(OH)2D3, and suppressed PTH. An exome sequencing analysis was carried out to determine the genetic variants associated with her disease. Bioinformatics tools were used to assess variant pathogenicity. We identify a novel homozygous mutation in the SLC34A1 gene, c.1361C>T; p.(T454M), and a previously described heterozygous SLC34A3 101 bp deletion. Mutation p.(T454M) affects transmembrane domain 5 of the NaPi-IIa protein, which is involved in substrate binding, probably impairing phosphate transport. Our results suggest the diagnosis of IIH type 2 in our patient and highlight the importance of exome analysis in diagnosing these tubulopathies. We suggest that the coexistent heterozygous SLC34A3 deletion could increase the risk of renal calcifications and the severity of other symptoms.

Hereditaryhypophosphatemic rickets with hypercalciuria ( HHRH) is a rare genetic condition with Autosomal recessive inheritance with a prevalence of 1 in 250000. It is due to mutation in SLC4A3 gene. Correct diagnosis of this condition is important as treatment with active vitamin D metabolites are contraindicated. Evolution of the disease despite initial completely normal bio chemistry has ben observed causing diagnostic confusion. First child presented at the age of 5.5 year with features of rickets. He had abnormal bone profile with normal vitamin D levels. urinary phosphate studies were compatible with HHRH. He was treated with phosphate supplementation and Potassium citrate. He has well responded to the treatment. Second child initially presented at 1.5 years of age with bowing and family history of hypercalciuria. All investigation findings including urinary phosphate studies were within normal limits. At the age of 2.5 year, he again presented with worsening of bowing. Bio chemical and urinary investigations were repeated. Laboratory findings were compatible with HHRH. It highlights the importance of repeated investigations despite initial normal parameters if the initial clinical suspicion is strong and clinical and investigation based diagnosis of this rare genetic disease in resource limited setting.

Hereditary hypophosphatemic rickets with hypercalciuria (HHRH), caused by SLC34A3 gene mutations, is characterized by hypophosphatemia, hypercalciuria, and low PTH levels. While rickets and skeletal deformities are common, HHRH also poses a significant risk for chronic kidney disease (CKD) due to nephrocalcinosis and recurrent kidney stones. Here, we describe a patient with mild skeletal deformities, who was diagnosed with HHRH during adolescence after undergoing whole genome sequencing (WGS) for suspected myopathy. Despite hypophosphatemia and low PTH, the patient had normal calcium levels and no nephrocalcinosis or kidney stones. X-rays showed mild metaphyseal changes consistent with rickets. While muscle weakness and pain are noted in X-linked hypophosphatemic rickets, neurological symptoms in HHRH tend to be milder. We present a patient with an unexpected homozygous likely pathogenic variant in the SLC34A3 gene. This case underscores the importance of distinguishing between skeletal, nephrological, and neurological conditions for accurate diagnosis, effective treatment, and genetic counseling.

Hereditary hypophosphatemic rickets with hypercalciuria (HHRH) is a rare fibroblast growth factor-23-independent disorder caused by biallelic variants in the SLC34A3 gene. The disease severity varies, and patients have an increased risk of developing renal complications. Phosphate supplementation is the standard of care and active vitamin D analogs are not indicated as they could worsen the hypercalciuria. We report a Brazilian girl with HHRH who presented with knee pain and progressive genu valgum deformity that became apparent from the age of eight years onwards. Nephrocalcinosis was also identified at age 13 years. Targeted next-generation sequencing for hereditary forms of rickets detected compound heterozygous pathogenic variants in SLC34A3, including a novel missense variant c.1217G>T (p.Gly406Val). Compliance to oral phosphorus therapy was suboptimal and adjunctive chlorthalidone therapy improved hypercalciuria. This report highlights the phenotypic variability and also expands the list of SLC34A3 variants associated with HHRH. An accurate diagnosis is key for optimal treatment. Of note, thiazide diuretics may be useful as adjunctive therapy for controlling hypercalciuria.