The activation-induced cytidine deaminase (AID) gene, specifically expressed in germinal center B cells in mice, is a member of the cytidine deaminase family. We herein report mutations in the human counterpart of AID in patients with the autosomal recessive form of hyper-IgM syndrome (HIGM2). Three major abnormalities characterize AID deficiency: (1) the absence of immunoglobulin class switch recombination, (2) the lack of immunoglobulin somatic hypermutations, and (3) lymph node hyperplasia caused by the presence of giant germinal centers. The phenotype observed in HIGM2 patients (and in AID-/- mice) demonstrates the absolute requirement for AID in several crucial steps of B cell terminal differentiation necessary for efficient antibody responses.

Griscelli syndrome (GS, MIM 214450), a rare, autosomal recessive disorder, results in pigmentary dilution of the skin and the hair, the presence of large clumps of pigment in hair shafts and an accumulation of melanosomes in melanocytes. Most patients also develop an uncontrolled T-lymphocyte and macrophage activation syndrome (known as haemophagocytic syndrome, HS), leading to death in the absence of bone-marrow transplantation. In contrast, early in life some GS patients show a severe neurological impairment without apparent immune abnormalities. We previously mapped the GS locus to chromosome 15q21 and found a mutation in a gene (MYO5A) encoding a molecular motor in two patients. Further linkage analysis suggested a second gene associated with GS was in the same chromosomal region. Homozygosity mapping in additional families narrowed the candidate region to a 3.1-cM interval between D15S1003 and D15S962. We detected mutations in RAB27A, which lies within this interval, in 16 patients with GS. Unlike MYO5A, the GTP-binding protein RAB27A appears to be involved in the control of the immune system, as all patients with RAB27A mutations, but none with the MYO5A mutation, developed HS. In addition, RAB27A-deficient T cells exhibited reduced cytotoxicity and cytolytic granule exocytosis, whereas MYO5A-defective T cells did not. RAB27A appears to be a key effector of cytotoxic granule exocytosis, a pathway essential for immune homeostasis.

Ataxia-telangiectasia (AT) is a human autosomal recessive disorder of childhood characterized by: (1) progressive cerebellar ataxia with degeneration of Purkinje cells; (2) hypersensitivity of fibroblasts and lymphocytes to ionizing radiation; (3) a 61-fold and 184-fold increased cancer incidence in white and black patients, respectively; (4) non-random chromosomal rearrangements in lymphocytes; (5) thymic hypoplasia with cellular and humoral (IgA and IgG2) immunodeficiencies; (6) elevated serum level of alphafetoprotein; (7) premature ageing; and (8) endocrine disorders, such as insulin-resistant diabetes mellitus. A DNA processing or repair protein is the suspected common denominator in this pathology. Heterozygotes are generally healthy; however, the sensitivity of their cultured cells to ionizing radiation is intermediate between normal individuals and that of affected homozygotes. Furthermore, heterozygous females are at an increased risk of breast cancer. These findings, when coupled with an estimated carrier frequency of 0.5-5.0%, suggest that (1) as many as one in five women with breast cancer may carry the AT gene and that (2) the increased radiation sensitivity of AT heterozygotes may be causing radiation therapists to reduce the doses of radiation used for treating cancer in all patients. To identify the genetic defect responsible for this multifaceted disorder, and to provide effective carrier detection, we performed a genetic linkage analysis of 31 families with AT-affected members. This has allowed us to localize a gene for AT to chromosomal region 11q22-23.

Griscelli syndrome (GS) is a rare autosomal recessive disorder that associates hypopigmentation, characterized by a silver-gray sheen of the hair and the presence of large clusters of pigment in the hair shaft, and the occurrence of either a primary neurological impairment or a severe immune disorder. Two different genetic forms, GS1 and GS2, respectively, account for the mutually exclusive neurological and immunological phenotypes. Mutations in the gene encoding the molecular motor protein Myosin Va (MyoVa) cause GS1 and the dilute mutant in mice, whereas mutations in the gene encoding the small GTPase Rab27a are responsible for GS2 and the ashen mouse model. We herein present genetic and functional evidence that a third form of GS (GS3), whose expression is restricted to the characteristic hypopigmentation of GS, results from mutation in the gene that encodes melanophilin (Mlph), the ortholog of the gene mutated in leaden mice. We also show that an identical phenotype can result from the deletion of the MYO5A F-exon, an exon with a tissue-restricted expression pattern. This spectrum of GS conditions pinpoints the distinct molecular pathways used by melanocytes, neurons, and immune cells in secretory granule exocytosis, which in part remain to be unraveled.

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Cell mediated immunity plays a critical role in human host defence against intracellular bacteria. In patients with unusual, severe infections caused by poorly pathogenic species of mycobacteria and salmonellae, genetic deficiencies have been identified in key genes in the type‐1 cytokine pathway, especially in IFNGR1 and IL12RB1. Here, we analyzed 11 patients originating from Turkey and suffering from unusual Mycobacterium bovis Bacille Calmette‐Guerin infections following vaccination, and found that most patients (n=8) are deficient in IL‐12Rβ1 expression and function. No defects were found in patients' IFN‐γR or IL‐18R. In addition, a first patient suffering from partial IL‐12Rβ1 deficiency is described. This patient presented with an intermediate cellular and immunological phenotype: a consistent, low response to IL‐12 was found, which could be further augmented by IL‐18. Despite a lack of cell surface IL‐12Rβ1 expression, normal levels of intracellular IL‐12Rβ1 protein were detectable, which was not seen in the other, completely IL‐12Rβ1 deficient patients examined. Moreover, this patient had a relatively mild clinical phenotype and was the only individual with a single homozygous amino acid substitution in IL‐12Rβ1 (C198R). Collectively, our findings indicate that idiopathic, unusually severe infections due to M. bovis BCG can be caused by complete as well as partial IL‐12Rβ1 deficiency.

The present study was undertaken in order to determine the possible alterations in whole saliva and the periodontal status in patients with diabetes mellitus (DM), and was conducted on 17 patients with DM and 17 systemically and periodontally healthy subjects. When the subjects were evaluated clinically, significantly increased probing depths were noticed in the DM group when compared with the healthy subjects. In whole saliva samples, sodium, potassium, total protein, amylase, thiocyanate, and secretory IgA levels were determined in both groups. Difference between the two groups regarding the mean salivary potassium levels were found to be statistically significant since the mean salivary potassium levels in the DM and the control groups were 2.470 +/- 9.04 mmol/L and 14.30 +/- 8.88 mmol/L, respectively. The mean salivary total protein, amylase and secretory IgA levels in the DM group were 2.41 +/- 1.0 mg/mL, 124.2 +/- 79.7 U/mL and 6.86 +/- 3.50 mg/L, all being significantly higher than the control group. However, no significant differences could be shown for the salivary sodium and thiocyanate levels. Nor was there any difference between non-insulin dependent diabetes mellitus (NIDDM) and insulin-dependent diabetes mellitus (IDDM). The findings of the present study suggest that, besides the clinical examinations, the determination of the possible alterations in the composition of whole saliva might also be helpful in understanding the increased severity of periodontal disease in diabetic patients.