Activation-induced Cytidine Deaminase Mutations Research Articles

A novel activation-induced cytidine deaminase mutation in an adult with hyper-immunoglobulin M syndrome

The hyper-immunoglobulin M (HIGM) syndromes are a group of immunodeficiencies that exhibit low or absent levels of immunoglobulin G (IgG), IgA, and IgE and normal to high levels of IgM.1 These syndromes are characterized by inherited defects in genes encoding for the CD40L or CD40 molecule, or defects in class-switch recombination (CSR) in B cells.2 Activation-induced cytidine deaminase (AID) is a protein that is required for CSR in B cell differentiation.3,4 A mutation in the activation-induced cytidine deaminase (AICDA) gene that encodes AID causes the autosomal recessive (AR) form of HIGM syndrome known as HIGM2.

Novel AICDA mutation in a case of autosomal recessive hyper-IgM syndrome, growth hormone deficiency and autoimmunity

BackgroundThe Hyper-immunoglobulin M syndromes (HIGM) are a heterogeneous group of genetic disorders, which have been rarely reported to be associated with growth hormone deficiency (GHD). Methods and resultsA nine-year-old girl with recurrent urinary tract infections, diarrhoea, sinopulmonary infections, and failure to thrive since the age of six months had normal CD3+, CD4+, CD8+T lymphocytes, and CD19+B lymphocytes and natural killer (NK) cells, but extremely elevated IgM and significantly decreased IgG and IgA. In view of the patient's short stature, growth hormone evaluation was carried out and growth hormone deficiency established. The patient underwent Ig replacement therapy and received growth hormone therapy in addition to antibiotics and responded well. Furthermore, the patient developed benign cervical lymphadenopathy, as well as elevated erythrocyte sedimentation rate, positive autoantibodies to SSA-Ro, and severely dry eyes, which partially responded to both the punctate occlusion and systemic corticosteroids, at the age of seven years. Sequencing analysis of the exons from activation-induced cytidine deaminase (AICDA) gene revealed that the patient was homozygous for a single T to C transversion at position 455 in exon 4, which replaces a Valine with an Alanine. ConclusionsTo our knowledge, this is a new AICDA mutation, which has not been reported previously in HIGM. The mutation analysis could improve diagnosis of HIGM patients and also elaborating on the spectrum of AICDA mutations.

Activation induced cytidine deaminase mutant (AID-His130Pro) from Hyper IgM 2 patient retained mutagenic activity on SHM artificial substrate

Activation induced cytidine deaminase (AID) is an essential enzyme for class switch recombination (CSR) and somatic hypermutation (SHM) during secondary immune response. Mutations in the AICDA gene are responsible for Hyper IgM 2 syndrome where both CSR and SHM or only CSR are affected. Indeed, triggering either of the two mechanisms requires the DNA deamination activity of AID. Besides, different domains of AID may be differentially involved in CSR and SHM through their interaction with specific cofactors. Herein, we studied the AID-induced SHM activity of the AID-His130Pro mutant identified in a patient with Hyper IgM 2 syndrome. AID mutagenic activity was monitored by the reversion of nonsense mutations of the EGFP gene assessed by flow cytometry. We found that the His130Pro mutation, which affects CSR, preserves AID mutagenic activity. Indeed, the His130 residue is located in a putative specific CSR region in the APOBEC-like domain, known to involve CSR specific cofactors that probably play a major role in AID physiological activities.

ASCIA‐P69: A NOVEL AICDA MUTATION IN A CASE OF AUTOSOMAL RECESSIVE HYPER‐IGM SYNDROME, GROWTH HORMONE DEFICIENCY AND AUTOIMMUNITY

The Hyper-immunoglobulin M syndromes (HIGM) or immunoglobulin class switch recombination (Ig-CSR) deficiencies are rare primary immunodeficiency (PID) disorders. A 9-year-old girl with recurrent ear infections and failure to thrive since the age of 6 months had normal lymphocyte subsets, but extremely elevated IgM and significantly decreased IgG and IgA. In view of the patient's short stature, growth hormone evaluation was carried out and growth hormone deficiency established. The patient underwent Ig replacement therapy and received short course of growth hormone therapy and responded well. Furthermore, the patient developed benign cervical lymphadenopathy, as well as elevated ESR, positive autoantibodies to SSA-Ro, and severely dry eyes, which partially responded to both the punctate occlusion and systemic corticosteroids, at the age of 7 years. Sequencing analysis of the exons from activation-induced cytidine deaminase ( AICDA ) gene revealed that the patient was homozygous for a single T to C transversion at position 455 in exon 4, which replaces a Valine with an Alanine. To our knowledge, this is a new AICDA mutation, which has not been reported previously in HIGM. Autoimmune complications have been formerly described in the reported series of AICDA deficient HIGM; however the association with growth hormone deficiency is rarely reported.

Clinical Features and Genetic Analysis of Taiwanese Patients With the Hyper IgM Syndrome Phenotype

Hyper IgM syndrome (HIGM), characterized by recurrent infections, low serum IgG and IgA, normal or elevated IgM, defective class switch recombination and somatic hypermutation, are heterogeneous disorders with at least 6 distinct molecular defects, including the CD40 ligand (CD40L) and the nuclear factor κB essential modulator (NEMO, also known as IKKγ) genes (both X-linked), the CD40, activation-induced cytidine deaminase (AICDA or AID), uracil-DNA glycosylase genes (autosomal recessive) and IκBα (IKBA) (autosomal dominant). Our objective was to determine the molecular basis and clinical features of Taiwanese patients with the HIGM phenotype. Clinical manifestations and candidate genes were analyzed in a nationwide population-based study. Among 14 patients (12 unrelated families) since 2003, 10 patents were identified (8 families) with CD40L mutations, including 2 novel deletions of "A" nucleotide (Del 347A and Del 366A), both frameshift and stop at the 127th location; 1 novel AID deletion mutation lack of the 37thAsp and 38th Ser; 1 ataxia-telangiectasia mutation; and 1 deletion of chromosome 1q42. An adult-onset patient with mutant (Thr254Met)CD40L had approximately 30% detectable affinity and therefore less severity. Memory B cells decreased in patients with CD40L and activation-induced cytidine deaminase mutations. Three mortalities encompassed renal cell carcinoma in 1 patient with (Tyr169Asn)CD40L, pneumothorax in 1 with (Tyr140Stop)CD40L and pneumonia after chemotherapy in an ataxia-telangiectasia patient. One patient without detectable genetic defects but normal lymphocyte proliferation resembled the mild form of common variable immune deficiency phenotype. In contrast to those with AICDA mutation, small chromosome 1 q42 deletion and unknown genetic defect, the majority (10/14; 71.4%) with CD40L mutations except (Thr254Met) and an ataxia-telangiectasia patient had the severe form of HIGM phenotype.

Case of a 10-Year-Old Boy with Hyper–Immunoglobulin M Immunodeficiency Caused by Activation-Induced Cytidine Deaminase Deficiency

We report the case of a 10-year-old boy, with a history of recurrent sinopulmonary infections, presenting with pneumococcal meningitis. Immune workup found low immunoglobulin G (IgG), IgA, and IgE and elevated IgM. Specific antibodies to pneumococcus, tetanus, and mumps were low. Genetic testing identified CD40L and uracil-DNA glycosylase as normal. Sequence analysis for mutations in activation-induced cytidine deaminase (AID) gene on chromosome 12p13 revealed a single missense mutation in exon 3 caused by a point mutation. AID is an enzyme that is specifically present in activated B cells and necessary for isotype switching. This case highlights the significance of AID deficiency in hyper-IgM immunodeficiency.

Biochemical Analysis of Hypermutational Targeting by Wild Type and Mutant Activation-induced Cytidine Deaminase

The synthesis of high affinity antibodies requires activation-induced cytidine deaminase (AID) to initiate somatic hypermutation and class-switch recombination. Here we investigate AID-catalyzed deamination of C --> U on single-stranded DNA and on actively transcribed closed circular double-stranded DNA. Mutations are initially favored at canonical WRC (W = A or T, R = A or G) somatic hypermutation hot spot motifs, but over time mutations at neighboring non-hot spot sites increase creating random clusters of mutated regions in a seemingly processive manner. N-terminal AID mutants R35E and R35E/R36D appear less processive and have altered mutational specificity compared with wild type AID. In contrast, a C-terminal deletion mutant defective in CSR in vivo closely resembles wild type AID. A mutational spectrum generated during transcription of closed circular double-stranded DNA indicates that wild type AID retains its specificity for WRC hot spot motifs within the confines of a moving transcription bubble while introducing clusters of multiple deaminations predominantly on the nontranscribed strand.

Mutations in activation-induced cytidine deaminase in patients with hyper IgM syndrome.

Recent studies have shown that mutations in a newly described RNA editing enzyme, activation-induced cytidine deaminase (AID), can cause an autosomal recessive form of hyper IgM syndrome. To determine the relative frequency of mutations in AID, we evaluated a group of 27 patients with hyper IgM syndrome who did not have defects in CD40 ligand and 23 patients with common variable immunodeficiency. Three different mutations in AID were identified in 18 patients with hyper IgM syndrome, including 14 French Canadians, 2 Lumbee Indians, and a brother and sister from Okinawa. No mutations were found in the remaining 32 patients. In the group of patients with hyper IgM syndrome, the patients with mutations in AID were older at the age of diagnosis, were more likely to have positive isohemagglutinins, and were less likely to have anemia, neutropenia, or thrombocytopenia. Lymphoid hyperplasia was seen in patients with hyper IgM syndrome and normal AID as well as the patients with hyper IgM syndrome and defects in AID.