Early-childhood body mass index and its association with the COVID-19 pandemic, containment measures and islet autoimmunity in children with increased risk for type 1 diabetes

Aims/hypothesis The aim of this study was to determine whether BMI in early childhood was affected by the COVID-19 pandemic and containment measures, and whether it was associated with the risk for islet autoimmunity. Methods Between February 2018 and May 2023, data on BMI and islet autoimmunity were collected from 1050 children enrolled in the Primary Oral Insulin Trial, aged from 4.0 months to 5.5 years of age. The start of the COVID-19 pandemic was defined as 18 March 2020, and a stringency index was used to assess the stringency of containment measures. Islet autoimmunity was defined as either the development of persistent confirmed multiple islet autoantibodies, or the development of one or more islet autoantibodies and type 1 diabetes. Multivariate linear mixed-effect, linear and logistic regression methods were applied to assess the effect of the COVID-19 pandemic and the stringency index on early-childhood BMI measurements (BMI as a time-varying variable, BMI at 9 months of age and overweight risk at 9 months of age), and Cox proportional hazard models were used to assess the effect of BMI measurements on islet autoimmunity risk. Results The COVID-19 pandemic was associated with increased time-varying BMI (β = 0.39; 95% CI 0.30, 0.47) and overweight risk at 9 months (β = 0.44; 95% CI 0.03, 0.84). During the COVID-19 pandemic, a higher stringency index was positively associated with time-varying BMI (β = 0.02; 95% CI 0.00, 0.04 per 10 units increase), BMI at 9 months (β = 0.13; 95% CI 0.01, 0.25) and overweight risk at 9 months (β = 0.23; 95% CI 0.03, 0.43). A higher age-corrected BMI and overweight risk at 9 months were associated with increased risk for developing islet autoimmunity up to 5.5 years of age (HR 1.16; 95% CI 1.01, 1.32 and HR 1.68, 95% CI 1.00, 2.82, respectively). Conclusions/interpretation Early-childhood BMI increased during the COVID-19 pandemic, and was influenced by the level of restrictions during the pandemic. Controlling for the COVID-19 pandemic, elevated BMI during early childhood was associated with increased risk for childhood islet autoimmunity in children with genetic susceptibility to type 1 diabetes. Graphical Abstract Supplementary Information The online version of this article (10.1007/s00125-023-06079-z) contains peer-reviewed but unedited supplementary material.

SNP data were generated as previously described ( 14) using the Infinium Global Screening Array (version 3.0, Illumina Inc.) performed on DNA extracted from dried blood spots of children for whom consent to store and use dried blood spots for additional research was provided.Samples were excluded if the genotype call rate was less than 95%, if there was a mismatch between genotyped sex and reported sex, or if there was an outlying heterozygosity rate (>3 SD at a minor-allele frequency [MAF] of <1% or MAF of ≥1%).Variants were filtered if the call rate was less than 98% or if the MAF was greater than 1%.Imputation of additional variants was performed using the Sanger Imputation Service (https://imputation.sanger.ac.uk/) and the Haplotype Reference Consortium reference panel (http://www.haplotype-reference-consortium.org/)HRC r1.1 2016 (GRCh3/hg19).

ESM Methods 2. Definition of islet autoimmunity outcome
Islet autoantibodies were measured centrally at 2 independent GPPAD Core laboratories, located at the Institute of Diabetes Research, Helmholtz Munich, Germany, and at the University of Bristol Medical School, Diabetes and Metabolism, Learning and Research, Southmead Hospital, Bristol, United Kingdom (for confirmation of results).Serum samples from each visit were measured for autoantibodies against insulin (IAA), glutamate decarboxylase-65 (GADA), insulinoma-associated antigen-2 (IA-2A), and zinc transporter-8 (ZnT8A) at the German laboratory.IAA were detected using a competitive radiobinding assay (RBA) with protein A/G immunoprecipitation and 125I-labeled recombinant human insulin.GADA and IA-2A were measured based on the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) harmonized assay protocol using 35Smethionine-labeled antigens produced by in vitro transcription and translation of N-terminally truncated GAD65 (amino acids 96-585) or IA-2ic (amino acids 606-979), encoded in the pTNT plasmid vector (Promega), as previously described.For GADA, ELISA (RSR Ltd.) was used as the second test if the RBA result was positive.ZnT8A was tested in separate assays to detect autoantibodies to the arginine 325R and tryptophan 325W human ZnT8 variants (ZnT8RA and transcribed/translated recombinant ZnT8 (amino acids 268-369), as previously described.Children were classified as ZnT8A positive if they were positive for ZnT8RA and/or ZnT8WA or as ZnT8A negative if the tests were negative for both antibody specificities.These RBAs had sensitivities and specificities of 54% and 99% for IAA, 66% and 99% for GADA, 76% and 100% for IA-2A, 56% and 99% for ZnT8RA, and 50% and 99% for ZnT8WA according to the Islet Autoantibody Standardization Program (IASP) 2016 Workshop.Samples that tested positive for islet autoantibodies at the Munich laboratory were sent to the second central autoantibody laboratory in Bristol for confirmatory testing.Here, IAA were assayed using a competition RBA with 125I-labeled human insulin, as previously described.GADA and IA-2A were assayed using the NIDDK harmonized assay protocol using 35S-methionine-labeled in vitro transcribed/translated recombinant full-length GAD65 or IA-2ic.ZnT8RA and ZnT8WA were tested in separate RBAs based on the NIDDK harmonized assay protocol.These RBAs had sensitivities and specificities of 54% and 99% for IAA, 74% and 97% for GADA, 70% and 100% for IA-2A, 60% and 100% for ZnT8RA, and 46% and 100% for ZnT8WA according to the IASP 2015 Workshop.If a sample tested positive for a specific autoantibody by tests at both laboratories, a subsequent sample was tested by both laboratories to confirm persistence of the islet autoantibody-positive status for the detected autoantibody.The risk score was calculated by multiplying the number of risk alleles (i.e. 0, 1 or 2 for each single SNP) with the weight assigned to each SNP and then summing up the weighted contributions of all SNPs.As an example, the risk score for a child, homozygous for the risk allele of rs13038017 (weight 0.054), heterozygous for the risk allele of rs148252705 (weight 0.157), homozygous for the non-risk allele of rs1830890 (weight 0. 067) and for all other SNPs in the BMI GRS is calculated as follows:

Table 2 .
SNPs used to calculate the BMI genetic risk score according to their association with early childhood BMI(1)

Table 4 .
Multivariate analysis on the effect of COVID-19 pandemic and on the effect of COVID-19 containment measures (Stringency Index) during COVID-19 pandemic on time-varying BMI-SDS, weight-for-length Z-Score and overweight (weight-for-length Z-score >2) at 9 months of age.
*adjusted for BMI GRS and country of residence, † adjusted for BMI GRS