Immunological manifestation of a patient carrying a de novo USB1 heterozygous variant. (A) The pedigree of the index family. (B) Serum IgA, IgM, IgG, IgG1, IgG2, IgG3, and IgG4 levels over time for the patient. (C) Neutrophils, leukocytes, lymphocytes, platelets, hemoglobin, and reticulocytes count over time for the patient. The grey area indicates the upper and lower reference boundaries across different ages. (D and E) Sanger sequencing analysis of gDNA from all family members (D) and USB1 cDNA from LCLs derived from the patient (P1) and a healthy donor (Ctr) (E). (F) Protein alignment of human USB1 with orthologs. The red arrow indicates the location of the residue mutated in the patient (P44).