CD4 and Bloom syndrome: Some BS patients, however, may present abnormal laboratory findings, such as reduction of serum immunoglobulin concentrations, decreased numbers of CD4‐positive T cells and impaired T cell proliferation in vitro, and impaired T helper cell function (Cunniff et al., 2017; Resende, Pereira, Melo, Santos, & Aguiar, 2007; Sanz, German, & Cunniff, 2016).