LAUSR

With interest, we read the paper of Bayramoğlu et al. [1], which showed an association between vitamin D deficiency and clinical severity in children and adolescents with COVID19. Besides the investigated parameters, we would like to highlight the potential influence of vitamin D binding protein (DBP) polymorphism on the reported findings. Being one of the most abundant serum proteins, DBP transports 85–90% of vitamin D metabolites, whereas 10–15% is more loosely bound to albumin and <0.1% circulates in an unbound form. DBP is characterized by three major alleles, determined by two SNPs (rs7041 and rs4588): DBP1F (rs7041-T/rs4588-C), DBP1S (rs7041-G/rs4588-C), and DBP2 (rs7041-T/rs4588-A), yielding six allelic combinations and corresponding phenotypes: 3 homozygous (DBP1F/1F, DBP 1S/1S, DBP 2/2) and 3 heterozygous (DBP 1F/2, DBP 1F/1S, DBP1S/2) [2]. The DBP gene is one of the genes involved in the variation of 25-hydroxy vitamin D (25OHD) concentrations. In several studies with adults and children, minor alleles of rs7041 and rs4588, but also of other DBP SNPs (rs2282679 and rs1155563), have been linkedwith lower 25OHD concentrations [3]. 25OHD and DBP concentrations are highest in DBP1-1, intermediate in DBP1-2, and lowest in DBP2-2 individuals [2]. In infants, the DBP1S/1S, DBP1S/1F, and DBP1F/1F group showed higher serum 25OHD concentrations from birth onward and a significantly better response to 24-month high-dose supplementation of 30 μg/day vitamin D3 in comparison with the DBP1S/2, DBP 1F/ 2, and DBP 2/2 group [3].Moreover, the DBP1 allele frequency has been associated with a lower prevalence and mortality due to a SARS-CoV-2 infection, which could be partly explained by potential protective effects of vitamin D and DBP (actin scavenging, hemotaxis, influence on T cell response, ...) [4]. In conclusion, the DBP polymorphism could influence the reported vitamin D concentrations in children with COVID19 and should be taken into account in future studies.