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Organization of the human CD40L gene: implications for molecular defects in X chromosome-linked hyper-IgM syndrome and prenatal diagnosis.

ABSTRACT: Recently, CD40L has been identified as the gene responsible for X chromosome-linked hyper-IgM syndrome (HIGM1). CD40L on activated T cells from HIGM1 patients fails to bind B-cell CD40 molecules, and subsequent analysis of CD40L transcripts by reverse transcription PCR demonstrated coding region mutations in these patients. This approach, however, is of limited use for prenatal diagnosis of HIGM1 in the early-gestation fetus. In this report, we have defined the genomic structure of the CD40L gene, which is composed of five exons and four intervening introns. With this information, we have defined at the genomic level the CD40L gene abnormalities for three previously described HIGM1 patients who demonstrated clustered deletions in the CD40L coding region. These different deletions arose from three distinct mechanisms, including (i) a splice donor mutation with exon skipping, (ii) a splice acceptor mutation with utilization of a cryptic splice site, and (iii) a deletion/insertion event with the creation of a new splice acceptor site. In addition, we have performed prenatal evaluation of an 11-week-old fetus at risk for HIGM1. CD40L genomic clones provide a starting point for further studies of the genetic elements that control CD40L expression. Our knowledge of the CD40L gene structure will prove useful for the identification of additional mutations in HIGM1 and for performing genetic counseling about this disease.

SUBMITTER: Villa A

PROVIDER: S-EPMC43319 | biostudies-other | 1994 Mar

REPOSITORIES: biostudies-other

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Project description:The X-linked hyper-immunoglobulin M syndrome (XHIGM) is an uncommon primary combined immunodeficiency disease caused by CD40L gene mutations. A delayed or missed diagnosis of XHIGM is common and concerning, owing to atypical immunoglobulin profile and phenotype of some patients, low recognition, and limited knowledge of clinicians on XHIGM in some underdeveloped areas. Opportunistic infections are a prominent clinical feature of XHIGM. However, toxoplasma encephalitis occurs sporadically and is extremely rare in patients with XHIGM.A 2 years and 10 months' old male suffered from 3 times of serious infection since 1 year and 4 months of age. Although with history of recurrent respiratory infections, protracted diarrhea, persistent or intermittent neutropenia companioned with oral ulcer, and a typical immunoglobulin profile during his second disease attack, the consideration of XHIGM was still completely ignored because of our low recognition and limited knowledge of this disorder. The diagnosis of XHIGM was ultimately confirmed by detection of elevated serum IgM concentration, decreased serum IgG and IgE concentration, and identification of a mutation c.654C>A (p.C218X) in CD40L gene. Given clinical manifestation of lethargy, uncontrollable somnolence and ataxia, a cat/dog exposure history, positive serum Toxoplasma gondii (T gondii) IgM, positive cerebrospinal fluid T gondii PCR results, and typical characteristics of brain magnetic resonance imaging as multiple rings liked nodules lesions in bilateral cerebral hemisphere cortex, bilateral basal ganglia, and dorsal thalamus, the diagnosis of toxoplasmic encephalitis was considered during his third disease attack. Thereafter, oral administration of sulfadiazine and azithromycin, intravenous immunoglobulin, and subcutaneous injection of G-CSF were initiated. Regrettably, the patient abandoned the treatment because of economic factor and died 3 months after discharge.A more thorough clinical history and some features like recurrent respiratory infections, protracted diarrhea, and persistent or intermittent neutropenia companioned with oral ulcer could increase clinical suspicion of XHIGM. Cerebral toxoplasmosis is rare in patients with XHIGM, but still should be considered. The present study firstly reported a delayed diagnosed case of XHIGM with CD40L gene c.654C>A (p.C218X) mutant complicated with toxoplasma encephalitis in Chinese population, which highlighted the importance of CD40-CD40L interaction in cell-mediated immunity against T gondii.

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Organization of the human CD40L gene: implications for molecular defects in X chromosome-linked hyper-IgM syndrome and prenatal diagnosis.

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