Refractory rickets in the tropics

Clinical characteristics and genetic profile of children with WDR72-associated distal renal tubular acidosis: a nationwide experience

BACKGROUND

Limited data, primarily from small case series, exist regarding the clinical profile, genetic variants, and outcomes of WDR72-associated distal renal tubular acidosis (WDR72-dRTA).

METHODS

Our study enrolled children diagnosed with WDR72-dRTA below 18 years of age from 9 Indian centers and analyzed their clinical characteristics, genetic profiles, and outcomes. Potential genotype-phenotype correlations were explored.

RESULTS

We report 22 patients (59% female) with WDR72-dRTA who were diagnosed at a median age of 5.3 (3, 8) years with polyuria (n = 17; 77.3%), poor growth (16; 72.7%), and rickets (9; 40.9%). Amelogenesis imperfecta was present in 21 (95.5%) cases. At presentation, all patients had normal anion gap metabolic acidosis; hypokalemia and nephrocalcinosis were seen in 17 (77.3%) patients each. Seven (31.8%) patients had concomitant proximal tubular dysfunction. Genetic analysis identified biallelic nonsense variants in 18 (81.8%) patients, including novel variants in 6 cases. A previously reported variant, c.88C > T, and a novel variant, c.655C > T, were the most frequent variants, accounting for 10 (45.5%) cases. Over a median follow-up of 1.3 (1, 8) years, the height velocity improved by 0.74 (0.2, 1.2) standard deviation scores, while 3 children (13.6%) progressed to chronic kidney disease (CKD) stage 2, with eGFR ranging from 67 to 76 mL/min/1.73 m2, respectively, after 11.3-16 years of follow-up. No specific genotype-phenotype correlation could be established.

CONCLUSIONS

WDR72-dRTA should be considered in children with typical features of amelogenesis imperfecta and dRTA. Biallelic nonsense variants are common in Asians. While most patients respond well to treatment with improved growth and preserved eGFR, on long-term follow-up, a decline in eGFR may occur.

Etiology, clinical characteristics, genetic profile, and outcomes of children with refractory rickets at a referral center in India: a cohort study

BACKGROUND

Limited research exists regarding the genetic profile, clinical characteristics, and outcomes of refractory rickets in children from India.

METHODS

Patients with refractory rickets aged ≤ 18 years were enrolled. Data regarding clinical features, etiology, genotype-phenotype correlation, and estimated glomerular filtration rate (eGFR) were recorded.

RESULTS

Seventy-two patients with refractory rickets (non-nutritional, with normal kidney function at presentation) from 65 families attending the pediatric nephrology clinic from 2005-2024 were included. Median (IQR) age at first presentation was 2 (1, 4) years. Clinical features included failure-to-thrive (49 [68.1%]), polyuria (37 [51.4%]), nephrocalcinosis (33 [45.8%]), fractures (10 [13.9%]), and hypokalemic paralysis (4 [5.6%]). Major etiologies included distal renal tubular acidosis (dRTA) [34(47.2%)], hereditary hypophosphatemic rickets (11 [15.3%]), cystinosis (9 [12.5%]), Lowe syndrome (3 [4.2%]), vitamin D-dependent rickets (4 [5.5%]), and Fanconi-Bickel syndrome (3 [4.2%]). Next-generation sequencing identified 61 variants among 71 children tested (85.9%), of which 56 variants (among 55 children) were pathogenic (P)/likely-pathogenic (LP) (77.5% diagnostic-yield). P/LP variants included SLC4A1 (n = 14), CTNS (n = 9), PHEX (n = 8), WDR72 (n = 5), OCRL (n = 2), SLC2A2 (n = 3), ATP6V0A4 (n = 4), VDR (n = 3), CLDN16 (n = 2), ATP6V1B1 (n = 1), SLC12A1 (n = 1), CLCN5 (n = 1), SLC34A3 (n = 1), ATP7B (n = 1), and KCNJ1 (n = 1). Fifteen novel P/LP variants and five novel variants-of-uncertain-significance (VUS) were identified. c.2573C > A in exon 19 among SLC4A1-dRTA (n = 14) was a recurrent mutation. Five patients with cystinosis, two patients with SLC4A1-dRTA, two with WDR72-dRTA, and two with Bartter syndrome showed progression to CKD stage 2 or greater during follow-up.

CONCLUSIONS

dRTA, X-linked hypophosphatemic rickets, and cystinosis were common causes of refractory rickets. The c.2573C > A variant in exon 19 was a recurrent mutation in SLC4A1-dRTA.

Etiology and Biochemical Profile of Rickets in Tertiary Care Centres in Eastern India: A Retrospective Cross-sectional Study

Introduction

We aimed to describe the clinical, biochemical and etiological profile of patients referred with a provisional diagnosis of rickets in tertiary care centres. In addition, we tried to propose a diagnostic algorithm for the evaluation of such patients.

Methods

This was a retrospective cross-sectional study conducted in two tertiary care centres of West Bengal. Data of patients were retrieved between 2014 and 2021.

Results

Out of 101 children, 22 had conditions simulating rickets. Renal tubular acidosis (RTA) was the most common (53.2%) etiology of rickets, followed by phosphopenic rickets (PR) (22.8%) and calcipenic rickets (CR) (17.7%). The prevalence of true nutritional rickets (NR) was only 8.9%. Children with RTA had a significantly higher prevalence of chronic ill health (69%) and polyuria (95.2%). Weight standard deviation score (SDS) and body mass index (BMI) SDS scores were significantly lower in the RTA group compared to others. Around 90.5% of children with RTA, and none in the other groups, had hypokalemia. Biochemically, hypophosphatemia and elevated alkaline phosphatase (ALP) were present in all patients with PR and CR. Compared to CR, median serum phosphate was significantly lower in the PR group. A significant difference in ALP values was noticed in patients with hypophosphatemia (815 ± 627 IU/L) compared to those without (279 ± 204 IU/L). Plasma parathyroid hormone (PTH) of 100 pg/ml seemed useful to differentiate CR from other forms.

Conclusion

NR is uncommon in tertiary care centres. Children with rickets should be approached systematically with the estimation of ALP, phosphorus, creatinine, calcium, PTH and 25-hydroxy vitamin D to reach an etiological diagnosis.

Importance of Dietary Phosphorus for Bone Metabolism and Healthy Aging

Inorganic phosphate (Pi) plays a critical function in many tissues of the body: for example, as part of the hydroxyapatite in the skeleton and as a substrate for ATP synthesis. Pi is the main source of dietary phosphorus. Reduced bioavailability of Pi or excessive losses in the urine causes rickets and osteomalacia. While critical for health in normal amounts, dietary phosphorus is plentiful in the Western diet and is often added to foods as a preservative. This abundance of phosphorus may reduce longevity due to metabolic changes and tissue calcifications. In this review, we examine how dietary phosphorus is absorbed in the gut, current knowledge about Pi sensing, and endocrine regulation of Pi levels. Moreover, we also examine the roles of Pi in different tissues, the consequences of low and high dietary phosphorus in these tissues, and the implications for healthy aging.

The Frequency of Clinical Manifestations of Hypophosphatemic Rickets in Patients with Therapeutic Strategies

The aim of this study was to evaluate the frequency of clinical manifestations of various types of rickets in patients could be effective in therapeutic strategies. A total of eleven child patients (7 females and 4 males) were included in the present study. The patients were admitted to the hospital with hypophosphatemic rickets. In our study, the age at the time of diagnosis ranged from 1 to15 years. Mean age of first presentations at final diagnosis was determined to be 5.5 an 2 years, respectively. Five patients out of 11 patients had showed significant history of vitamin D3 resistance. Family history of similar skeletal problems was reported to be positive in six patients. Furthermore, there were seven relative marriages in parents. Mean value of Gomez index has been revealed as 64%. Mean serum phosphate level was detected as 2.9 mg/dL, that this level in males (2.2 mg/dL) was significantly less than females (3.4 mg/dL) (P=0.5). Mean serum alkaline phosphatase activity was reached 913 IU/L. Alkaline phosphatase activity in women (1075 IU/L) was significantly lower than that of men (750 IU/L), (P=0.5). Definitive treatment with oral phosphate and vitamin D3 can prevent complications of the disease and the side effects of unconventional treatments.

Hypophosphatemic rickets

Hypophosphatemic rickets is a disorder of bone mineralization caused due to defects (inherited/acquired) in the renal handling of phosphorus. This group includes varied conditions, X-linked hypophosphatemic rickets being the most common inheritable form of rickets. The other common forms are autosomal dominant hypophosphatemic rickets and tumor-induced osteomalacia. Although these conditions exhibit different etiologies, increased phosphatonins form a common link among them. Fibroblast growth factor 23 (FGF23) is the most widely studied phosphatonin. Genetic studies tend to show that the phosphorus homeostasis depends on a complex osteo-renal axis, whose mechanisms have been poorly understood so far. Newer disorders are being added as the mechanisms in this axis get discovered. This review focuses on the clinical, biochemical, genetic features and management of hypophosphatemic disorders leading to defective mineralization.