Reduced secreted μ mRNA synthesis in selective IgM deficiency of Bloom's syndrome

• Published in: Clinical and experimental immunology 1992-04, Vol.88 (1), p.35-40
• Main Authors: KONDO, N., OZAWA, T., KATO, Y., MOTOYOSHI, F., KASAHARA, K., KAMEYAMA, T., ORII, T.
• Format: Article
• Language: English
• Subjects: Adult; Base Sequence; Biological and medical sciences; Bloom Syndrome - immunology; Bloom's syndrome; Chromosome fragility (bloom syndrome, ataxia telangiectasia, fanconi anemia, x-linked mental retardation...); Female; Genes, Immunoglobulin; Humans; Immunoglobulin M - deficiency; Immunoglobulin M - genetics; Immunoglobulins - biosynthesis; Lymphocyte Activation; Male; Medical genetics; Medical sciences; Molecular Sequence Data; RNA, Messenger - biosynthesis; secreted μ C terminal mRNA; secreted μ mRNA synthesis; selective IgM deficiency
• ISSN: 0009-9104; 1365-2249
• DOI: 10.1111/j.1365-2249.1992.tb03035.x

SUMMARY Serum IgM concentrations were low although serum IgG and IgA concentrations were normal in both our patients with Bloom's syndrome. Although the percentages of surface Ig‐earing cells were not reduced, the numbers of Ig‐ecreting cells were markedly reduced. The membran‐ound μ(μm) and secreted μ (μs) mRN As arc produced from transcripts of a single immunoglobulin μ gene by alternative RNA processing pathways. The control of μs mRNA synthesis depends on the addition of poly(A) to μs ‐erminal segment. In both patients, μ mRNA was well detected but μs ‐erminal mRNA was scarcely detected, suggesting that μ mRNA was well transcribed but μs mRNA was not. There was, at least, no mutation or deletion in the μs ‐erminal coding sequence, the RNA splice site (GG/TAAAC) at the 5’ end of μs ‐erminal segment and the AATAAA poly(A) signal sequence in both patients. Our results suggest that selective IgM deficiency in Bloom's syndrome is due to an abnormality in the maturation of surface Ig‐earing B cells into Ig‐ecreting cells and a failure of μs mRNA synthesis. Moreover, reduced μs mRNA synthesis may be due to the defect on developmental regulation of the site at which poly(A) is added to transcripts of the μ gene.