Refractory rickets caused by mild distal renal tubular acidosis

Screening for an Underlying Tubulopathy in Children With Growth Failure, Simply Maths?

BACKGROUND

Involving pediatric nephrological input in the clinical diagnostic work-up of children with short stature, gave rise to the hypothesis that the presence of an underlying renal tubular disorder in children with short stature is possibly underestimated. This study focussed on the added value of calculated urinary fractional excretion (FE) in the early detection of tubular disorders in children with growth failure.

METHODS

This trial was designed as an observational study analyzing the medical files of children between 5 and 16 years who had been referred for short stature to the pediatric endocrinology outpatient clinic at the University Hospital Antwerp between 25/01/2015 and 01/03/2019. Based on the laboratory results of the simultaneously taken blood and urine sample, the fractional excretions of Sodium, Chloride, Potassium, Calcium, Phosphate, and Magnesium were calculated.

RESULTS

Of the 299 patients, 54 patients had at least one deviating fractional excretion value, requiring further investigation (control sample of blood and urine, kidney ultrasound or 24 h urine collection). Genetic screening for tubulopathies was performed in 19 patients. In 5 patients (1.7% of the total population) a tubulopathy was confirmed based on genetic analysis.

CONCLUSION

This study explored the possibility of using fractional excretions as a screening test to obtain an earlier diagnosis of tubular disorders in children with short stature. Of the 299 patients, 5 patients were diagnosed with a genetically confirmed tubulopathy. Based on these results, we propose a flowchart for an additional work-up in all children with a deviating fractional excretion.

Genetics of Refractory Rickets: Identification of Novel PHEX Mutations in Indian Patients and a Literature Update

Refractory rickets is a genetic disorder that cannot be treated by vitamin D supplementation and adequate dietary calcium and phosphorus. Hereditary hypophosphatemic rickets is one of the major forms of refractory rickets in Indian children and caused due to mutations in the PHEX , FGF23 , DMP1 , ENPP1 , and SLC34A3 genes. This is the first study in India on a large number of patients reporting on mutational screening of the PHEX gene. Direct sequencing in 37 patients with refractory rickets revealed eight mutations in 13 patients of which 1 was nonsense, 2 were deletions, 1 was a deletion-insertion, and 4 were missense mutations. Of these mutations, four (c.566_567 delAG, c.651_654delACAT, c.1337delinsAATAA, and c.2048T > A) were novel mutations. This article discusses the mutations in Indian patients, collates information on the genetic causes of refractory rickets, and emphasizes the significance of genetic testing for precise diagnosis, timely treatment, and management of the condition, especially in developing countries.