This finding might be explained by the absence of terminal deoxynucleotidyl transferase (TdT) expression before the third trimester, which results in a lack of random nontemplated (N) nucleotide insertions to rearranged CDR3 regions7,63–65 or by the fact that B cell receptor rearrangements with long CDR3 sequences are more prone to mediate autoimmunity and are therefore preferentially removed during cell maturation66. The gene discussed is DNTT; the disease is Autoimmunity.