Elisa Holmlund-Suila

Objectives: Benign transient hyperphosphatasemia (BTH) is characterized by markedly elevated serum alkaline phosphatase (ALP) in young children without clinical signs of hepatobiliary or metabolic bone disease. BTH is typically discovered incidentally, and its etiology and ALP isoform profile is largely unexplored. Methods: We identified 63 children with BTH at 1 or 2 years of age within the VIDI study, a randomized-controlled vitamin D supplementation trial, initially comprising 987 infants followed longitudinally to 6–8 years of age. Assessments included total ALP, bone ALP (BALP) and liver ALP isoforms by gel electrophoresis with lectin precipitation, BALP Ostase ^® immunoassays (Liaison ^® and IDS-iSYS analyzers), and BALP isoforms (B/I, B1 and B2) by HPLC. Results: In children with BTH, total ALP levels reached up to 11-fold above the upper reference interval limit, while BALP was increased 2- to 17-fold. Gel electrophoresis showed increased bone, liver 1 and liver 2 ALP levels, with pronounced anodal migration of liver ALP in BTH. In contrast, children with non-typical BTH, defined by the absence of pronounced anodal migration of liver ALP, had relatively higher bone ALP than liver ALP levels. HPLC profiling revealed that the BALP B2 isoform was increased in BTH. Conclusions: BTH was associated with concurrent elevation of bone and liver ALP isoforms and characteristic anodal migration, likely reflecting enhanced sialylation resulting in prolonged serum half-life. Increased expression of the BALP B2 isoform and specific liver ALP isoforms suggests differential glycosylation. Site-specific glycoproteomic analyses are warranted to define ALP glycoform signatures underlying BTH.

Vitamin D is suggested to impact neurodevelopment, yet the current evidence is conflicting. We tested if vitamin D ₃ supplementation during the first two years of life, maternal 25-hydroxy-vitamin D (25(OH)D) concentration during pregnancy, and child’s 25(OH)D concentrations at 12 and 24 months are associated with neurocognitive abilities in 6.6-8.9-year-old children. Participants were from a Finnish vitamin D double-blind randomized clinical trial and classified themselves white. Children received either vitamin D ₃ 400-IU ( n = 189) or 1200-IU ( n = 209) daily until 24 months of age. Serum 25(OH)D was analyzed from mothers at mean of 11.2 weeks of gestation, and from children at 12.0 and 23.9 months (25(OH)D, mean (SD) = 83.8 (21.7), 102.3 (30.1), 105.5 (28.6) nmol/L, respectively). Total Intelligence quotient (IQ) score was assessed with Wechsler Intelligence Scale for Children (WISC-IV) and executive functioning with A Developmental Neuropsychological Assessment (NEPSY-II) and parent-rated Behavior Rating Inventory of Executive Function (BRIEF) questionnaire. Neurocognitive abilities at age 6–8 years did not differ between the supplementation groups or according to 25(OH)D concentration at 12 or 24 months (total IQ: β = 1.14, 95% CI -1.69;3.97, p = 0.43, executive functioning, NEPSY-II: β =-0.07, 95% CI -0.14;0.28, p = 0.49, executive functioning, BRIEF: β =-0.42, 95% CI -5.13;4.28, p = 0.86). Maternal 25(OH)D was not associated with executive functioning. However, both lower and higher maternal 25(OH)D concentrations during pregnancy were associated with child’s lower total IQ scores (vertex at 76.6 nmol/L, quadratic estimate p < 0.001) supporting the hypothesis of the role of vitamin D during fetal development. The study is registered with ClinicalTrials.gov (NCT01723852, 2012-11-07 and NCT04302987, 2020-03-06).

Context Childhood hyperphosphatasemia is usually transient and may associate with infections. It remains less well known how hyperphosphatasemia is related to growth and bone mineralization. Objectives We explored alkaline phosphatase (ALP) concentrations and prevalence of hyperphosphatasemia, and their association with vitamin D, growth, infections, and bone parameters in healthy children. Design and Methods The study was a secondary analysis of a vitamin D intervention trial. Participants received vitamin D₃ 10 or 30 µg daily from age 2 weeks to 2 years. Children with data on ALP at 12 and/or 24 months (N = 813, girls 51.9%) were included. Anthropometrics and bone parameters were measured at 12 and 24 months. Infections were recorded prospectively by the parents. Results Boys had higher ALP than girls at 12 months (median [IQR] 287 [241 to 345] U/L vs. 266 [218 to 341] U/L; p = 0.02). At 24 months concentrations were lower than at 12 months (240 [202 to 284]; p < 0.001) but without sex difference. The prevalence of hyperphosphatasemia (ALP >1000 U/L) at 12 months was 5.3% (female: male ratio 2:1, p = 0.062) and at 24 months 0.6%. Body size, growth rate and bone mineral content associated positively with ALP, while vitamin D intervention had no effect. Infants with hyperphosphatasemia were smaller and had lower bone mineral content. Hyperphosphatasemia did not associate with previous infections. Conclusions Approximately 5% of infants had hyperphosphatasemia at 12 months, but <1% at 24 months. ALP concentrations and hyperphosphatasemia associated with sex, anthropometry, and bone mineralization. Infections did not contribute to hyperphosphatasemia.

Context Phosphate homeostasis and its modifiers in early childhood are inadequately characterized. Objective To determine physiological plasma phosphate concentration and modifying factors in healthy infants at 12 to 24 months of age. Design This study included 525 healthy infants (53% girls), who participated in a randomized vitamin D intervention trial and received daily vitamin D₃ supplementation of either 10 or 30 μg from age 2 weeks to 24 months. Biochemical parameters were measured at 12 and 24 months. Dietary phosphate intake was determined at 12 months. Main Outcome Measures Plasma phosphate concentrations at 12 and 24 months of age. Results Mean (SD) phosphate concentration decreased from 12 months (1.9 ± 0.15 mmol/L) to 24 months (1.6 ± 0.17 mmol/L) of age (P < 0.001 for repeated measurements). When adjusted by covariates, such as body size, creatinine, serum 25-hydroxyvitamin D, intact and C-terminal fibroblast growth factor 23, mean plasma phosphate was higher in boys than girls during follow-up (P = 0.019). Phosphate concentrations were similar in the vitamin D intervention groups (P > 0.472 for all). Plasma iron was associated positively with plasma phosphate at both time points (B, 0.006 and 0.005; 95% CI, 0.004-0.009 and 0.002-0.008; P < 0.001 at both time points, respectively). At 24 months of age, the main modifier of phosphate concentration was plasma creatinine (B, 0.007; 95% CI 0.003-0.011, P < 0.001). Conclusion Plasma phosphate concentration decreased from age 12 to 24 months. In infants and toddlers, the strongest plasma phosphate modifiers were sex, iron, and creatinine, whereas vitamin D supplementation did not modify phosphate concentrations.

Context The relationship between maternal and infant vitamin D and early childhood growth remains inadequately understood. Objective To investigate how maternal and child 25-hydroxyvitamin D [25(OH)D] and vitamin D supplementation impact growth during the first 2 years of life. Design A randomized, double-blinded intervention study. Setting A single-center study from pregnancy until offspring age 2 years. Participants Altogether 812 term-born children with complete data, recruited at Maternity Hospital. Intervention Children received daily vitamin D₃ supplementation 10 μg (Group-10) or 30 μg (Group-30) from age 2 weeks to 2 years. Main outcome measures Anthropometry and growth rate at age 1 and 2 years. Results Toddlers born to mothers with Pregnancy 25(OH)D >125 nmol/L were at 2 years lighter and thinner than the reference group with 25(OH)D 50-74.9 nmol/L (P<0.010). Mean 2-year 25(OH)D concentrations were 87 nmol/L in Group-10 and 118 nmol/L in Group-30 (P0.053), but Group-30 had slower growth in length and head circumference between 6 months and 1 year (P<0.047), and more rapid growth in weight and length-adjusted weight between 1 and 2 years (P121 nmol/L) were shorter (mean difference 0.2 SD score (SDS), P=0.021), lighter (mean difference 0.4 SDS, P=0.001) and thinner (in length-adjusted weight) (mean difference 0.4 SDS, P=0.003) compared with the lowest quartile (<81.2 nmol/L). Conclusion Vitamin D and early childhood growth may have an inverse U-shaped relationship.

Maternal vitamin D deficiency remains a substantial health problem in many areas. In addition to nutritional factors and the use of vitamin D supplements, other factors, such as genetic determinants and the current Western indoor lifestyle, affect not only vitamin D status but also bone strength and mineral accrual. Many health authorities recommend maternal vitamin D supplementation to prevent vitamin D deficiency and associated adverse pregnancy and offspring outcomes.¹ Commonly, daily supplementation of 400 to 600 IU of vitamin D is recommended for pregnant women. Identify all potential conflicts of interest that might be relevant to your comment. Conflicts of interest comprise financial interests, activities, and relationships within the past 3 years including but not limited to employment, affiliation, grants or funding, consultancies, honoraria or payment, speaker's bureaus, stock ownership or options, expert testimony, royalties, donation of medical equipment, or patents planned, pending, or issued. Err on the side of full disclosure. If you have no conflicts of interest, check "No potential conflicts of interest" in the box below. The information will be posted with your response. Not all submitted comments are published. Please see our commenting policy for details.

Vitamin D is important for normal skeletal homeostasis, especially in growing children. There are no previous genome-wide association (GWA) studies exploring genetic factors that influence vitamin D metabolism in early childhood. We performed a GWA study on serum 25-hydroxyvitamin D (25(OH)D) and response to supplementation in 761 healthy term-born Finnish 24-month-old children, who participated in a randomized clinical trial comparing effects of 10 μg and 30 μg of daily vitamin D supplementation from age 2 weeks to 24 months. Using the Illumina Infinium Global Screening Array, which has been optimized for imputation, a total of 686085 markers were genotyped across the genome. Serum 25(OH)D was measured at the end of the intervention at 24 months of age. Skeletal parameters reflecting bone strength were determined at the distal tibia at 24 months using peripheral quantitative computed tomography (pQCT) (data available for 648 children). For 25(OH)D, two strong GWA signals were identified, localizing to GC (Vitamin D binding protein) and CYP2R1 (Vitamin D 25-hydroxylase) genes. The GWA locus comprising the GC gene also associated with response to supplementation. Further evidence for the importance of these two genes was obtained by comparing association signals to gene expression data from the Genotype-Tissue Expression project and performing colocalization analyses. Through the identification of haplotypes associated with low or high 25(OH)D concentrations we used a Mendelian randomization approach to show that haplotypes associating with low 25(OH)D were also associated with low pQCT parameters in the 24-month-old children. In this first GWA study on 25(OH)D in this age group we show that already at the age of 24 months genetic variation influences 25(OH)D concentrations and determines response to supplementation, with genome-wide significant associations with GC and CYP2R1. Also, the dual association between haplotypes, 25(OH)D and pQCT parameters gives support for vertical pleiotropy mediated by 25(OH)D. The effect of vitamin D continues to be highly debated in various health outcomes, including bone health. In this study first study of children this young we searched for genes that modify vitamin D metabolism in early childhood using a genome-wide analysis of almost 700,000 genetic variants in a cohort of 761 healthy children participating in a vitamin D intervention study. We show that genetic variation in the genes coding for Vitamin D binding protein (GC) and Vitamin D 25-hydroxylase (CYP2R1) are important determinants for serum 25-hydroxyvitamin D concentration in 2-year-old children. Genetic variants within the GC gene also affect how the child responds to vitamin D supplementation. Moreover, our findings suggest that in 2-year-old children vitamin D concentration, even when within the normal range, influences bone strength as children with genetic constellations associating with lower vitamin D concentration and poorer response to vitamin D supplementation also have weaker bones.

Context: Single nucleotide polymorphisms (SNPs) of the vitamin D binding protein encoding the GC (group component) gene affect 25-hydroxyvitamin D (25OHD) concentrations, but their influence on vitamin D status and response to vitamin D supplementation in infants is unknown.Objective: To study GC genotype–related differences in 25OHD concentrations and the response to supplementation during a vitamin D intervention study in infants.Design: In this randomized controlled trial, healthy term infants received vitamin D3 (10 or 30 μg/d) from 2 weeks to 24 months of age. GC SNPs rs2282679, rs4588, rs7041, and rs1155563 were genotyped. rs4588/7041 diplotype and haplotypes of rs2282679, rs4588, and rs7041 (Haplo3SNP) and of all four SNPs (Haplo4SNP) were determined.Main Outcome Measures: 25OHD measured in cord blood at birth and at 12 and 24 months during intervention.Results: A total of 913 infants were included. Minor allele homozygosity of all studied GC SNPs, their combined haplotypes, and rs4588/rs7041 diplotype 2/2 were associated with lower 25OHD concentrations at all time points in one or both intervention groups [analysis of covariance (ANCOVA) P < 0.043], with the exception of rs7041, which did not affect 25OHD at birth. In the high-dose supplementation group receiving 30 μg/d vitamin D3, but not in those receiving 10 µg/d, genotype of rs2282679, rs4588, and rs7041; diplotype; and Haplo3SNP significantly affected intervention response (repeated measurement ANCOVA Pinteraction < 0.019). Minor allele homozygotes had lower 25OHD concentrations and smaller increases in 25OHD throughout the intervention.Conclusions: In infants, vitamin D binding protein genotype affects 25OHD concentration and efficiency of high-dose vitamin D3 supplementation.