Scientists combing through hundreds of high-quality human genome assemblies have discovered a hidden layer of variation in the genes that build the light chains of human antibodies. Using the standardized IMGT annotation framework, researchers led by Maria Georga and Sofia Kossida catalogued the kappa (IGK) and lambda (IGL) immunoglobulin loci across two reference genomes and more than a hundred chromosomal-level haploid assemblies representing all major human superpopulations.
The light chain loci are essential components of the adaptive immune system. Together with the heavy chain, one of these loci forms the antigen-binding site of every antibody, shaping its specificity, affinity, and molecular behavior. Combinatorial pairing of heavy and light chains multiplies the diversity of the human antibody repertoire enormously. Yet despite this central role, the genomic architecture of IGK on chromosome 2 and IGL on chromosome 22 has remained incompletely resolved, particularly regarding structural variation across individuals from different ancestral backgrounds.
The difficulty stems from the organization of these regions. Unlike the single, contiguous heavy chain locus, the light chain genes are split across two chromosomes. The IGK locus is especially treacherous for genome assemblers: it contains two large, inverted, highly similar clusters of variable genes, termed proximal and distal, followed by the joining and constant genes. IGL, by contrast, features a tandem array of variable genes followed by J–C clusters. Both loci display extensive sequence similarity among their genes and considerable allelic diversity, characteristics that have historically produced assembly errors and gaps in the reference genomes. GRCh38, the standard human reference, captures only a portion of each locus.
To overcome these obstacles, the team assembled a dataset of unprecedented scale for this purpose. From 554 publicly available human chromosomal assemblies on NCBI as of 15 July 2025, they filtered down to 144 high-quality germline assemblies for the IGK locus and 127 for IGL, representing African, Admixed American, East Asian, European, and South Asian superpopulations. Complete IMGT annotation was performed on the T2T-CHM13 and GRCh38 reference assemblies for IGL, and on T2T-CHM13 and the NA19240_mat_hprc_f2 assembly for IGK.
Among the IGK discoveries, one of the novel functional genes corresponds to the previously non-localized gene IGKV1-NL1, now renamed IGKV1D-7-1 and detected between IGKV3D-7 and IGKV1D-8. Two further functional genes, IGKV1-40-1 and its duplicated, inverted counterpart IGKV1D-40-1, were absent from GRCh38, likely due to sequencing errors, but have now been fully annotated. Two novel duplicated pseudogenes, IGKV(II)-26-1 and IGKV(II)D-26-1*01, were identified in the proximal and distal regions respectively. The three functional IGKV alleles correspond to sequences recently reported by an independent study, providing additional validation of their existence.
The most prevalent structural variant at the kappa locus was an insertion of the novel gene IGKV1D-7-1, detected in 30 of the 144 assemblies and absent in 114. Its frequency varied strikingly across superpopulations: present in 5.5% of European assemblies (1/22), 12.5% of South Asian (3/24), and 10.7% of Admixed American (3/28), but in 31.4% of African (11/35) and 35.5% of East Asian (11/31) assemblies. Comparisons between African and Admixed American, and between East Asian and South Asian, did not reach statistical significance at roughly p = 0.07, which the authors attribute to limited sample sizes.
More dramatic structural differences also emerged. A large-scale deletion removing the complete distal region of the IGK locus appeared in 5 of 144 assemblies, spanning two European, one Admixed American, one East Asian, and one South Asian haplotype; in these, IGKV1D-40-1 was the only distal variable gene remaining. A rare proximal deletion removing genes from IGKV2-29 to IGKV1-5 was observed in a single assembly. Three further assemblies shared a family of overlapping deletions in the proximal region, differing in upstream starting points but all terminating at the same gene, IGKV6-21. Given the repetitive nature of the locus, sequencing or assembly artifacts cannot be fully excluded, though the absence of gaps and the repeated pattern across independent assemblies may indicate a potential genomic hotspot near IGKV6-21.
The lambda locus told a different story. Sixteen novel IGLV genes were identified, and 22 new alleles within existing IGLV genes, all pseudogenes. Overall gene content at IGL was highly conserved, with most deviations representing individual cases rather than systematic population-specific patterns. One notable exception was IGLV5-39, a functional gene that exhibited recurrent absence in 75 of 127 assemblies. Its presence was confirmed in 52 assemblies, consistently localized between IGLV(I)-42 and IGLV(VII)-41-1. Although the graph suggested that European and Admixed American genomes had roughly equal likelihood of carrying the gene while other populations were more likely to lack it, pairwise Fisher’s exact tests did not reach statistical significance, meaning these differences could not be confirmed with the current sample sizes.
Individual genomes carried their own surprises. The paternal assembly of one Southern Han Chinese individual lacked 11 consecutive IGLV3 and IGLV2 subgroup genes across roughly 9.3 kilobases with no sequence gaps, suggesting a possible structural deletion absent from the maternal assembly of the same person. A Gujarati Indian assembly showed a block of seven genes missing between IGLV4-60 and IGLV11-55, spanning 13 kilobases compared with 52 kilobases in the reference. In the constant region, the team confirmed potential copy number variations, with multiple assemblies exhibiting duplications of J–C clusters and some showing triplications.
The findings carry practical weight beyond cataloguing. IGKV2D-40, in which a novel allele was identified, has been reported as a candidate biomarker in tendon healing and venous thrombosis and linked to prognosis in head and neck squamous cell carcinoma and colorectal cancer, while IGKV2D-28, carrying another novel SNP, has been reported as a potential biomarker for gestational diabetes mellitus. The functional consequences of these polymorphisms remain undetermined. On the lambda side, IGLV6-57, associated with AL amyloidosis, was found in 129 assemblies, supporting its consistent germline presence. The authors acknowledge that current sub-population sample sizes are not exhaustive and frame the work as a foundational characterization of light chain diversity. The expanded IMGT reference set now offers an improved framework for studying antibody repertoires, immunogenetic variation, monoclonal antibody development, and population-level diversity, with further data needed to capture rare variants and complete the picture of population-specific differences.
Subject of Research: Discovery of novel immunoglobulin kappa and lambda light-chain genes, alleles, and structural variants across diverse human populations
Article Title: Novel genes and polymorphisms in human immunoglobulin light chains across diverse populations
Article References: Georga, M., Papadaki, A., Folch, G., Jabado-Michaloud, J., Zeitoun, G., Duroux, P., Giudicelli, V., & Kossida, S. (2026). Novel genes and polymorphisms in human immunoglobulin light chains across diverse populations. Genes & Immunity. https://doi.org/10.1038/s41435-026-00416-z
Image Credits: AI Generated
DOI: 10.1038/s41435-026-00416-z
Keywords: immunoglobulin light chain, IGK locus, IGL locus, IMGT annotation, structural variation, novel genes, allelic diversity, genome assemblies, population immunogenetics, antibody repertoire, T2T-CHM13, GRCh38
News Source: Juliet Wilcox. (November 5, 2026). Scientists uncover dozens of new antibody light-chain genes hidden in diverse human genomes. Scienmag.
