Fibroblast growth factor 23 (FGF23) was identified at the turn of the century as the long-sought circulating phosphatonin in human pathology. Since then, several clinical and experimental studies have investigated the metabolism of FGF23 and revealed its relevant pathogenic role in various diseases. Most of these studies have been performed in adult individuals. However, the mineral metabolism of the child is, to a large extent, different from that of the adult because, in addition to bone remodeling, the child undergoes a specific process of endochondral ossification responsible for adequate mineralization of long bones’ metaphysis and growth in height. Vitamin D metabolism is known to be deeply involved in these processes. FGF23 might have an influence on bones’ growth as well as on the high and age-dependent serum phosphate concentrations found in infancy and childhood. However, the interaction between FGF23 and vitamin D in children is largely unknown. Thus, this review focuses on the following aspects of FGF23 metabolism in the pediatric age: circulating concentrations’ reference values, as well as those of other major variables involved in mineral homeostasis, and the relationship with vitamin D metabolism in the neonatal period, in vitamin D deficiency, in chronic kidney disease (CKD) and in hypophosphatemic disorders.

To assess if serum free 25-hydroxyvitamin D (25OHD) is a better indicator of vitamin D status than total 25OHD in healthy children. Cross-sectional prospective clinical study was designed. We measured serum free 25OHD concentrations and its correlation with calculated free 25OHD, total 25OHD, intact parathyroid hormone (PTH), and vitamin D binding protein (DBP) in children. The influence of age, sex, ethnicity, body mass index (BMI), season of the year, diet intake, vitamin supplements, time spent outdoors and albumin concentrations on free 25OHD was also analyzed. 241 children aged from 0 days to 14 years, and living in the northern Spain (latitude 43° N), were included. Mean (SD) free 25OHD concentrations were 2.48 (1.39), 5.46 (3.12), 4.12 (1,72), 3.82 (1.43) pg/ml in children aged 0 days, 1 month-2 years, 2–6 years and >6 years, respectively. Correlation between directly measured and calculated free 25OHD was high and significant (r = 0.66) as well as the correlation between serum free and total 25OHD concentrations (r = 0.61). No significant correlation was found between PTH and free 25OHD (r = -0.08). The total 25OHD and PTH concentrations’ correlation was inverse (r = -0.25) and significant. Neither free nor total 25OHD concentrations correlated with DBP concentrations. Among the analyzed variables, free 25OHD values were higher in spring/summer than in autumn/winter in children older than 6 years. : These findings do not support that free 25OHD is a better marker of vitamin D deficiency than total 25OHD in healthy pediatric population.

Enteroviruses (EVs) are a large group of genotypes that cause a variety of pathologies, some of them very serious. This study analyzed the last 10 years (2014–2023) of EVs diagnosis and classification. In 166,674 samples collected, EVs were found in 9,535 (5.7%) by rt-RT-PCR, and 332 (3.5%) were classified by Sanger methods. Symptoms were analyzed in 7623 cases. EVs were found in 5718/63,829 (8.9%) before, 1384/42,373 (3.3%) during and 2433/60,472 (4%) after the Covid pandemic (p < 0.0001), and in 7249/69,700 (10.4%) children under 6 years and in 2286/96,974 (2.35%) in oldest (p < 0.0001). The positive rate of EVs was high but decreased during the Covid period. In the youngest children EVs-A (associated with exantematohous disorders as well as respiratory manifestations and febrile syndromes) was most common, while EVs-B (frequent in neurological symptoms) was most common in children aged 6–15 years and EVs-D (associated to respiratory manifestations) in adults.