Since the initial report of X-linked agammaglobulinemia by Bruton, numerous autosomal primary immune deficiencies affecting early B-cell differentiation have been described in humans. The identification of these autosomal mutations has been facilitated by phenotype comparison with knockout mice. In mice, defects in B-cell development have been observed after disruption of genes encoding transcription factors, the interleukin-7 pathways as well as structural or signaling components of the pre-B-cell receptor. In general, the phenotypes of primary immune deficiencies in humans correlate with those observed in mutant mice, validating the use of the mouse model approach. In addition, we report a follow-up analysis of an autosomal primary deficiency in a young female patient born from consanguinous parents and characterized by the absence of pre-B and B-cell compartments. The patient's gene defect was identified as a cytosine insertion at the beginning of the CH1 exon of the Ig (mu) gene, resulting in a stop codon at position 48 and the absence of Ig (mu) chain expression. The precise phenotype of this patient is compared to other autosomal primary immunodeficiencies affecting humans and mice.