Growth hormone treatment improves final height in children with X-linked hypophosphatemia

X-linked hypophosphataemia

X-linked hypophosphataemia is a genetic disease caused by defects in the phosphate regulating endopeptidase homolog X-linked (PHEX) gene and is characterised by X-linked dominant inheritance. The main consequence of PHEX deficiency is increased production of the phosphaturic hormone fibroblast growth factor 23 (FGF23) in osteoblasts and osteocytes. Chronic exposure to circulating FGF23 is responsible for renal phosphate wasting and decreased synthesis of calcitriol, which decreases intestinal phosphate absorption. These mechanisms result in lifelong hypophosphataemia, impaired growth plate and bone matrix mineralisation, and diverse manifestations in affected children and adults, including some debilitating morbidities and possibly increased mortality. Important progress has been made in disease knowledge and management over the past decade; in particular, targeting FGF23 is a therapeutic approach that has substantially improved outcomes. However, patients affected by this complex disease need lifelong care and innovative treatment strategies, such as gene repair of PHEX, are necessary to further limit the disease burden.

Calcium, Phosphate, and Vitamin D in Children and Adolescents with Chronic Diseases: A Cross-Sectional Study

Chronic diseases may affect the nutritional status of children and adolescents. Calcium (Ca), phosphorus (P), and vitamin D (Vit-D) are crucial nutrients for their growth and development. Proper diagnosis and treatment are critical components of personalized and precision medicine. Hence, we conducted a cross-sectional and comparative study to evaluate Ca, P, and Vit-D levels in their non-skeletal functions and their association with health and nutritional biomarkers in children and adolescents with diverse chronic conditions. We performed anthropometric, body composition, clinical evaluation, biochemical analysis, and dietary survey methods. A total of 78 patients (1-19 years, 43 females, 42 children) took part in this study. Overall, 24, 30, and 24 participants were obese, undernourished, and eutrophic, respectively. Results found that 74% and 35% of individuals had deficient Vit-D and Ca intake, respectively. Most cases were normocalcemic. Results also found that 47% of the subjects had Vit-D deficiency (VDD), 37% were insufficient, and 37% had hypophosphatemia. Of the 46% and 31% of patients with VDD and insufficient levels, 19% and 11% were hypophosphatemic, respectively. Calcium, P, and Vit-D levels were associated with anthropometric parameters, body mass index, body composition, physical activity, diet, growth hormones, and the immune, liver, and kidney systems. These results show the coincident risk of altered Ca, P, and Vit-D metabolism in children and adolescents with chronic diseases.

Clinical, genetic profile and therapy evaluation of 11 Chinese pediatric patients with Fanconi-Bickel syndrome

BACKGROUND

Fanconi-Bickel syndrome (FBS) is a rare autosomal recessive disorder characterized by impaired glucose and galactose utilization as well as proximal renal tubular dysfunction.

METHODS

Clinical, biochemical, genetic, treatment, and follow-up data for 11 pediatric patients with FBS were retrospectively analysed.

RESULTS

Hepatomegaly (10/11), short stature (10/11) and hypophosphataemic rickets (7/11) were the most common initial symptoms. At diagnosis, all patients had decreased fasting blood glucose (FBG), plasma bicarbonate (HCO3-) and serum phosphorus, as well as elevated liver transaminases, alkaline phosphatase (AKP) and proximal renal tubular dysfunction. Two infant patients were misdiagnosed with transient neonatal diabetes mellitus. After therapy with uncooked cornstarch and conventional rickets treatment, remission of hepatomegaly was observed in all patients, with significant improvements in pre-prandial blood glucose, liver transaminases, triglyceride, plasma HCO3- and AKP (p < 0.05). At the last follow-up, 5/7 patients with elevated AKP had nephrocalcinosis. The mean height standard deviation score (Ht SDS) of eight patients with regular treatment increased from - 4.1 to -3.5 (p = 0.02). Recombinant human growth hormone (rhGH) was administered to 4/9 patients, but their Ht SDS did not improve significantly (p = 0.13). Fourteen variants of the SLC2A2 gene were identified, with six being novel, among which one was recurrent: c.1217T > G (p.L406R) (allele frequency: 4/22, 18%). Patients with biallelic missense variants showed milder metabolic acidosis than those with null variants. Two of five patients from nonconsanguineous families with rare homozygous variations showed 5.3 Mb and 36.6 Mb of homozygosity surrounding the variants, respectively; a region of homozygosity (ROH) involving the entire chromosome 3 covering the SLC2A2 gene, suggesting uniparental disomy 3, was detected in one patient.

CONCLUSIONS

Early diagnosis of FBS is difficult due to the heterogeneity of initial symptoms. Although short stature is a major issue of treatment for FBS, rhGH is not recommended in FBS patients who have normal GH stimulation tests. Patients with biallelic null variants may require alkali supplementation since urine bicarbonate loss is genetically related. ROH is a mechanism for rare homozygous variants of FBS in nonconsanguineous families.

Linear growth of children with X-linked hypophosphatemia treated with burosumab: a real-life observational study

To assess the long-term efficacy of burosumab for pediatric patients with X-linked hypophosphatemia, focusing on linear growth. This multi-center retrospective study included 35 pediatric patients who began treatment with burosumab between January 2018 and January 2021. We collected clinical data, anthropometric measurements, laboratory results, and Rickets Severity Score (RSS), from 2 years prior to treatment initiation and up to 4 years after. Burosumab was initiated at a mean age of 7.5 ± 4.4 years (range 0.6-15.9), with a mean initial dose of 0.8 ± 0.3 mg/kg, which was subsequently increased to 1.1 ± 0.4 mg/kg. The patients were followed for 2.9 ± 1.4 years (range 1-4) after initiating burosumab. Serum phosphorus levels increased from 2.7 ± 0.8 mg/dl at burosumab initiation to 3.4 ± 0.6 mg/dl after 3 months and remained stable (p < 0.001). Total reabsorption of phosphorus increased from 82.0 ± 6.8 to 90.1 ± 5.3% after 12 months of treatment (p = 0.041). The RSS improved from 1.7 ± 1.0 at burosumab initiation to 0.5 ± 0.6 and 0.3 ± 0.6 after 12 and 24 months, respectively (p < 0.001). Both height z-score and weight z-score improved from burosumab initiation to the end of the study: from - 2.07 ± 1.05 to - 1.72 ± 1.04 (p < 0.001) and from - 0.51 ± 1.12 to - 0.11 ± 1.29 (p < 0.001), respectively. Eight children received growth hormone combined with burosumab treatment. Height z-score improved among those who received growth hormone (from - 2.33 ± 1.12 to - 1.94 ± 1.24, p = 0.042) and among those who did not (from - 2.01 ± 1.01 to - 1.66 ± 1.01, p = 0.001).

CONCLUSION

 Burosumab treatment in a real-life setting improved phosphate homeostasis and rickets severity and enhanced linear growth.

WHAT IS KNOWN

• Compared to conventional therapy, burosumab treatment has been shown to increase serum phosphate levels and reduce the severity of rickets. • The effect of burosumab on growth is still being study.

WHAT IS NEW

• Height z-score improved between the start of burosumab treatment and the end of the study (-2.07 ± 1.05 vs. -1.72 ± 1.04, p < 0.001). • Eight children received burosumab combined with growth hormone treatment without side effects during the concomitant treatments.

Adult height improved over decades in patients with X-linked hypophosphatemia: a cohort study

OBJECTIVES

The aim of this study is to analyze height after cessation of growth (final height [FH]) and its evolution over the last decades in X-linked hypophosphatemia (XLH) patients in France, as the data on natural history of FH in XLH are lacking.

DESIGN

We performed a retrospective observational study in a large cohort of French XLH patients with available data on FH measurements.

MATERIALS AND METHODS

We divided patients into 3 groups according to their birth year: group 1 born between 1950 and 1974, group 2 born between 1975 and 2000, and group 3 born between 2001 and 2006, respectively, and compared their FHs.

RESULTS

A total of 398 patients were included. Mean FHs were the following: for group 1, -2.31 ± 1.11 standard deviation score (SDS) (n = 127), 156.3 ± 9.7 cm in men and 148.6 ± 6.5 cm in women; for group 2, -1.63 ± 1.13 SDS (n = 193), 161.6 ± 8.5 cm in men and 153.1 ± 7.2 cm in women; and for group 3, -1.34 ± 0.87 SDS (n = 78), 165.1 ± 5.5 cm in men and 154.7 ± 6 cm in women. We report a significant increase in mean FH SDS over 3 generations of patients, for both men and women (P < .001). Final height SDS in male (-2.08 ± 1.18) was lower than in female (-1.70 ± 1.12) (P = .002).

CONCLUSION

The FH of XLH patients in France increased significantly over the last decades. Even though men's FHs improved more than women's, men with XLH remain shorter reflecting a more severe disease phenotype. While the results are promising, most patients with XLH remain short leaving room for improvement.