Age-related changes in serum immunoglobulins in patients with familial IgA deficiency and common variable immunodeficiency (CVID)

Innate Mechanisms in Selective IgA Deficiency

Selective IgA deficiency (SIgAD), characterized by a serum IgA level below 0.07 mg/ml, while displaying normal serum levels of IgM and IgG antibodies, is the most frequently occurring primary immunodeficiency that reveals itself after the first four years after birth. These individuals with SIgAD are for the majority healthy and even when they are identified they are usually not investigated further or followed up. However, recent studies show that newborns and young infants already display clinical manifestations of this condition due to aberrancies in their immune defense. Interestingly, there is a huge heterogeneity in the clinical symptoms of the affected individuals. More than 50% of the affected individuals do not have clinical symptoms, while the individuals that do show clinical symptoms can suffer from mild to severe infections, allergies and autoimmune diseases. However, the reason for this heterogeneity in the manifestation of clinical symptoms of the individuals with SIgAD is unknown. Therefore, this review focusses on the characteristics of innate immune system driving T-cell independent IgA production and providing a mechanism underlying the development of SIgAD. Thereby, we focus on some important genes, including TNFRSF13B (encoding TACI), associated with SIgAD and the involvement of epigenetics, which will cover the methylation degree of TNFRSF13B, and environmental factors, including the gut microbiota, in the development of SIgAD. Currently, no specific treatment for SIgAD exists and novel therapeutic strategies could be developed based on the discussed information.

BACH2 immunodeficiency illustrates an association between super-enhancers and haploinsufficiency

The transcriptional programs that guide lymphocyte differentiation depend on the precise expression and timing of transcription factors (TFs). The TF BACH2 is essential for T and B lymphocytes and is associated with an archetypal super-enhancer (SE). Single-nucleotide variants in the BACH2 locus are associated with several autoimmune diseases, but BACH2 mutations that cause Mendelian monogenic primary immunodeficiency have not previously been identified. Here we describe a syndrome of BACH2-related immunodeficiency and autoimmunity (BRIDA) that results from BACH2 haploinsufficiency. Affected subjects had lymphocyte-maturation defects that caused immunoglobulin deficiency and intestinal inflammation. The mutations disrupted protein stability by interfering with homodimerization or by causing aggregation. We observed analogous lymphocyte defects in Bach2-heterozygous mice. More generally, we observed that genes that cause monogenic haploinsufficient diseases were substantially enriched for TFs and SE architecture. These findings reveal a previously unrecognized feature of SE architecture in Mendelian diseases of immunity: heterozygous mutations in SE-regulated genes identified by whole-exome/genome sequencing may have greater significance than previously recognized.

Transient hypogammaglobulinaemia of infants in children with mastocytosis - strengthened indications for vaccinations

Mastocytosis is a disease caused by the accumulation of mast cells (MC) in the skin and/or in other tissues. Both the cutaneous form of the disease (CM) predominating in children and the systemic form (SM) typical for adults are associated with the occurrence of MC mediator-related symptoms. The release of mediators can be induced by physical stimuli and/or specific triggering factors. The routine vaccination program performed in the majority of children in infancy can be considered as an additional factor provoking exacerbation of CM. Conscious of the important role of MC in the innate immunity, we have analysed retrospective data concerning the levels of immunoglobulins, an adaptive factor, in a group of 74 infants and toddlers with CM. The values corresponding to transient hypogammaglobulinaemia of infants (THI) were found in 8 (10.81%) of cases. Classification of the antibody deficiency was done according to the working definitions for clinical diagnosis of primary immunodeficiency of the European Society of Immunodeficiencies (ESID) Registry - version May 11, 2015. Following the retrospective data, the final diagnosis of THI cannot be made due to the young age of the study group. The percentage may significantly exceed the published incidence of THI, i.e. about 0.11%. The results of our study may indicate, importantly, a higher incidence of THI in childhood-onset mastocytosis than in the general paediatric population and strengthen indications for vaccinations. In conclusion, we suggest that THI may be considered as a new aspect of paediatric mastocytosis that requires further investigation.

Bryant V, Frede N, Slade C, Woon ST, Lehnert K, Winzer S, Bulashevska A, Scerri T, Leung E, Jordan A, Keller B, de Vries E, Cao H, Yang F, Schäffer A, Warnatz K, Browett P, Douglass J, Ameratunga R, van der Meer J, Grimbacher B. Haploinsufficiency of the NF-κB1 Subunit p50 in Common Variable Immunodeficiency

Common variable immunodeficiency (CVID), characterized by recurrent infections, is the most prevalent symptomatic antibody deficiency. In ∼90% of CVID-affected individuals, no genetic cause of the disease has been identified. In a Dutch-Australian CVID-affected family, we identified a NFKB1 heterozygous splice-donor-site mutation (c.730+4A>G), causing in-frame skipping of exon 8. NFKB1 encodes the transcription-factor precursor p105, which is processed to p50 (canonical NF-κB pathway). The altered protein bearing an internal deletion (p.Asp191_Lys244delinsGlu; p105ΔEx8) is degraded, but is not processed to p50ΔEx8. Altered NF-κB1 proteins were also undetectable in a German CVID-affected family with a heterozygous in-frame exon 9 skipping mutation (c.835+2T>G) and in a CVID-affected family from New Zealand with a heterozygous frameshift mutation (c.465dupA) in exon 7. Given that residual p105 and p50—translated from the non-mutated alleles—were normal, and altered p50 proteins were absent, we conclude that the CVID phenotype in these families is caused by NF-κB1 p50 haploinsufficiency.

Reversal of Immunoglobulin A Deficiency in Children

PURPOSE

Immunoglobulin A deficiency (IgAD) is the most common primary immunodeficiency in the general population. It is defined as a serum IgA level below or equal to 0.07 g/l with normal IgM and IgG levels in children over the age of 4. However, a few cases of reversal of IgAD at later ages have been observed previously, especially in pediatric patients. This study aimed at investigating the frequency of reversal in a large cohort of children and young adults in order to evaluate the present definition of IgAD.

METHODS

Clinical laboratory records from 654 pediatric IgA deficient patients, 4-13 years of age, were retrieved from five university hospitals in Sweden. Follow up in the children where IgA serum levels had been routinely measured was subsequently performed. In addition, follow up of the IgA-levels was also performed at 4, 8 and 16 years of age in children who were IgA deficient at the age of 4 years in a Swedish population-based birth cohort study in Stockholm (BAMSE).

RESULTS

Nine out of 39 (23.1%) children who were identified as IgAD at 4 years of age subsequently increased their serum IgA level above 0.07 g/L. The average age of reversal was 9.53 ± 2.91 years. In addition, 30 out of the 131 (22.9%) children with serum IgAD when sampled between 5 and 9.99 years of age reversed their serum IgA level with time. The BAMSE follow up study showed a reversal of IgAD noted at 4 years of age in 8 out of 14 IgAD children at 16 years of age (5 at 8 years of age) where 4 were normalized their serum IgA levels while 4 still showed low serum levels of IgA, yet above the level defining IgAD. The results indicate that using 4 years of age, as a cut off for a diagnosis of IgAD may not be appropriate.

CONCLUSIONS

Our findings suggest that a diagnosis of IgAD should not be made before the early teens using 0.07 g/L of IgA in serum as a cut off.

IgA deficiency and autoimmunity

IgA is the most abundant immunoglobulin in the human body, and performs a very specialized role which involves mucosal immunity, development of tolerance and protection against infection. IgA is the key immunoglobulin in the respiratory and gastrointestinal tracts, which provide the most intimate interface between the environment and self. Normal levels of IgA are based on early studies consisting of only small numbers of patients. The international consensus definition of IgA deficiency is a level of 0.07g/l after the age of four years in the absence of IgG and IgM deficiencies. The epidemiology of IgA deficiency reveals interesting variances between geographical regions - the incidence in Caucasians being much higher than that in Asians. IgA deficiency has also been found to co-exist with autoimmune diseases, allergies and malignancies. The association with autoimmunity is particularly interesting because it suggests a common genetic linkage that could potentially also explain the diversity in geoepidemiology. Both MHC and non-MHC associations have been described and the 8.1 haplotype has been significantly associated with autoimmunity in IgA deficiency patients over controls. Non-MHC genetic associations include IFIH1 and CLEC16A. The mutations leading to IgA deficiency have not been defined, but in some cases of IgA deficiency it has been suggested that the pathogenesis involves a failure in switched memory B cells that can lead to this cohort experiencing an increased incidence of recurrent bacterial infections or autoimmune diseases. Attempts to investigate the role of cytokines that can induce IgA synthesis in cells of patients with IgA deficiency, such as IL21 or the combination of CD40L/anti-CD40, IL-4 and IL10, are underway.

Asthma and risk of selective IgA deficiency or common variable immunodeficiency: a population-based case-control study

OBJECTIVE

To determine the association between a history of asthma and a diagnosis of selective IgA deficiency (sIgAD)/common variable immunodeficiency (CVID).

PATIENTS AND METHODS

This population-based case-control study included residents of Olmsted County, Minnesota, who met the Pan-American Group for Immunodeficiency/European Society for Immunodeficiencies diagnostic criteria for sIgAD/CVID between January 1, 1964, through December 31, 2008. Each case had 4 age- and sex-matched controls (2 from the community and 2 from a list of individuals who had undergone an immune work-up). We ascertained asthma status by applying predetermined criteria for asthma.

RESULTS

We identified 39 cases: 26 (66.7%) had sIgAD and 13 (33.3%) had CVID. Of the 39 cases, 51.3% were men (n=20) and 97.1% were white (33 of 34 patients). The mean age at the index date (the time when criteria were met) of sIgAD/CVID was 34.2 years. Of the 39 cases, 9 (23.1%) had a history of asthma before the index date of sIgAD/CVID; of the 156 controls, 16 (10.3%) had a history of asthma before the index date (odds ratio, 2.77; 95% CI, 1.09-7.06; P=.03). A history of asthma (before or after the index date of sIgAD/CVID) was more prevalent in sIgAD/CVID cases (30.8%; n=12) than in matched controls (11.5%; n=18) (odds ratio, 3.57; 95% CI, 1.50-8.51; P=.01).

CONCLUSION

Asthmatic patients are more likely to have a diagnosis of sIgAD/CVID than nonasthmatic individuals. This association may potentially account for the increased risks of bacterial infections in some individuals with asthma.

Salivary immunoglobulin classes in Nigerians with periodontitis

AIM

To provide information on the usefulness of salivary immunoglobulin classes in the diagnosis of periodontitis.

MATERIALS AND METHODS

About 5 ml of unstimulated saliva was collected from 25 newly diagnosed subjects with periodontitis and 21 sex/age-matched apparently healthy individuals into plain sample bottles. The samples were collected between 9 am and 11 am at least, 1 hour after eating or washing of mouth and levels of salivary immunoglobulin classes (IgA, IgG, IgE and IgM) were determined using enzyme-linked immunosorbent assay (ELISA).

RESULTS

Only the mean level of IgA was significantly raised (p = 0.05) in the saliva of periodontitis patients compared with controls. The mean levels of IgG, IgM and IgE were not significantly elevated in patients with periodontitis, when compared with controls (p > 0.05).

CONCLUSION

This study showed that elevated salivary levels of IgA could be used as a screening tool for periodontitis.

CLINICAL SIGNIFICANCE

Identification of patients at risk and the diagnosis of active phases of periodontal disease remains a challenge due to lack of laboratory test routinely employed in the diagnosis and monitoring of patients with periodontal disease. This study showed that elevated salivary levels of immunoglobulin classes especially, IgA could be used as a screening tool for periodontitis.

Study of patients with Hyper-IgM type IV phenotype who recovered spontaneously during late childhood and review of the literature

Hyper-IgM syndromes are characterized by normal or elevated serum IgM levels with the absence or reduced levels of other immunoglobulins. There are some patients with defective class-switch recombination (CSR) who do not have CD40L, CD40, AID, and UNG defects. The aim of this study is to determine the B-cell functions of patients with Hyper-IgM type 4 phenotype. Ten patients (seven males and three females) 84.2 ± 16.5 months of age with initial low serum IgG and IgA and high or normal IgM levels were included. Clinically, 50% had recurrent upper respiratory tract, 10% urinary tract, 10% lower respiratory tract infections, and 30% had mixed type infections. Lymphoid hyperplasia, overt autoimmune manifestations, or malignancy was not noted. Seven of 10 patients were studied twice; at the age of 34.2 ± 13.7 and at 86.6 ± 12.3 months. Absolute lymphocyte counts and lymphocyte subsets were normal in all cases. All of them had normal expression of CD40 on B cells and CD40L on activated T cells for males. At first examination, all patients had normal in vitro sCD40L+rIL-4-induced B cell proliferation response and somatic hypermutation but CSR towards IgE was absent. AID and UNG genes did not show any abnormalities. All showed improvement in both clinical findings and Ig levels during the follow-up period of 55.8 ± 14.8 months. Ages for normalization of IgG and IgA were 68.2 ± 8.7 and 70.2 ± 21.6 months, respectively. During the second evaluation: In vitro sCD40L+rIL-4-induced B-cell proliferation was normal in all cases, whereas CSR was still abnormal in five of eight patients. Two of the patients had an increase in in vitro CSR response but still low IgG2 subclass levels. Three patients with initially absent in vitro CSR response also normalized.

CONCLUSION

Clinical manifestations and immunoglobulin levels of the patients with Hyper-IgM type 4 phenotype recovered in late childhood at about 6 years of age. There was a transient CSR defect which was not observed in cases with transient hypogammaglobulinemia of infancy. Detection of a non-AID or non-UNG associated CSR defect in infancy should be confirmed later on since spontaneous recovery may occur.

Outcome of hypogammaglobulinemia in children: immunoglobulin levels as predictors

We evaluated 131 children (M=88, F=43) with hypogammaglobulinemia. Data was analyzed mainly for delineating predictor factors for outcome. The distance from the lower limit of normal (-2SD) for any single measurement of immunoglobulins (Ig) was calculated and transformed into Ig scores. Mean age and duration of follow-up were 5.06 ± 4.05 and 3.7 ± 3.03 years, respectively. The diagnoses were: 22 CVID, 16 IgA deficiency, 33 transient hypogammaglobulinemia of childhood (THC), 3 selective IgM deficiency and 57 unclassified hypogammaglobulinemia (UCH). Low IgA scores (<-0.124) at presentation were indicative of subsequent development of IgA deficiency or CVID, whereas low IgM score (<-0.038) pointed towards more severe and persistent phenotypes. Combination of low IgM score between 2 and 5 years, impaired antibody response and low B cell counts enabled us to predict persistence of hypogammaglobulinemia beyond 5 years (specificity=90.5% and PPV=94.9%) and chronic lung disease (sensitivity=90.4% and specificity=68.3%). The set of criteria including low IgM scores, impaired antibody response and low B cell counts provided a high predictive value in detecting those with persistent hypogammaglobulinemia.

The B-cell compartment in the peripheral blood of children with different types of primary humoral immunodeficiency

The aim of this study was to evaluate the B-cell compartment in the peripheral blood of children with different types of hypogammaglobulinemia: common variable immunodeficiency (CVID), transient hypogammaglobulinemia of infancy (THI), and selective IgA deficiency (SIgAD). We analyzed by flow cytometry the changes in the B-cell subsets with age and showed that children with an early-onset CVID develop similar pattern of B-cell subsets as adult patients with CVID with age, as the levels of memory B cells (CD19/CD27) and class-switched memory B cells (CD19/CD27/IgD/IgM), in contrast to age-matched control group, did not increase with age. Children with SIgAD displayed similar changes as patients with CVID only within the class-switched memory B-cell subpopulation. No significant differences in the level of memory B cells and class-switched memory B cells in children with THI in comparison to age-matched control group were observed. There were no differences in the percentage of immature B cells (CD19/CD21) among all studied groups. As B-cell subsets in children with THI were normal during entire period of hypogammaglobulinemia, the persistence of low levels of memory B-cell subsets in some children may facilitate the diagnosis of CVID.

Common variable immunodeficiency in children

PURPOSE OF REVIEW

Common variable immunodeficiency is the most common primary immunodeficiency that needs medical attention. Symptoms may occur at any time, with two major peaks of onset at 5-10 and 20-30 years. We present the different clinical phenotypes of common variable immunodeficiency, review recent genetic findings and point to current treatment strategies.

RECENT FINDINGS

Five genes, ICOS, CD19, TNFRSF13B, TNFRSF13C and MSH5, have been found to be mutated in patients with common variable immunodeficiency. Additional possible genetic loci for autosomal dominant forms were detected on chromosomes 4q and 16q. These findings illustrate the heterogeneous molecular basis of common variable immunodeficiency and indicate the value of genetic linkage studies, thereby improving the genetic diagnosis.

SUMMARY

In young patients with unusually frequent bacterial infections, common variable immunodeficiency should always be considered as a differential diagnosis. The compulsory individual work-up should comprise a family history in order to document siblings and additional family members suffering from common variable immunodeficiency and/or selective IgA deficiency. Since the recently found gene defects affect a minority of patients with common variable immunodeficiency only, future genetic research is required to identify further susceptibility genes involved in the pathogenesis of this condition.

Deconstructing common variable immunodeficiency by genetic analysis

Common variable immunodeficiency (CVID) is the most common symptomatic primary immunodeficiency. Patients have recurrent bacterial infections and an increased risk of developing autoimmune diseases, lung damage, and selected cancers. Since 2003, four genes have been shown to be mutated in CVID patients: ICOS, TNFRSF13B (encoding TACI), TNFRSF13C (encoding BAFF-R) and CD19. Heterozygous mutations in TNFRSF13B are also associated with CVID, whereas the other three genes are purely recessive. Recent genetic linkage studies have also identified possible loci for dominant CVID genes on chromosomes 4q, 5p and 16q. These findings markedly improved the genetic diagnosis of CVID and point towards new strategies for future genetic studies. In addition, some CVID genes might be relevant to more common diseases such as asthma and stroke.

A propósito de um caso de imunodeficiência comum variável – Revisão das hipogamaglobulinemias

Common variable immunodeficiency is a primary immune deficiency characterized by heterogeneous immunologic disorders of unknown etiology. Its clinical manifestations include recurrent infections, autoimmune diseases, lymphoid hyperplasia, granulomatous diseases and malignancy. It can appear in patients with immunoglobulin A deficiency. The authors report the clinical case of a patient with common variable immunodeficiency and history of respiratory infections from the age of 9 months old, associated with the appearing of bronchiectasis.

Linkage of autosomal-dominant common variable immunodeficiency to chromosome 4q

The phenotype of common variable immunodeficiency (CVID) is characterized by recurrent infections owing to hypogammaglobulinemia, with deficiency in immunoglobulin (Ig)G and at least one of IgA or IgM. Family studies have shown a genetic association between CVID and selective IgA deficiency (IgAD), the latter being a milder disorder compatible with normal health. Approximately 20-25% of CVID cases are familial, if one includes families with at least one case of CVID and one of IgAD. Nijenhuis et al described a five-generation family with six cases of CVID, five cases of IgAD, and three cases of dysgammaglobulinemia. We conducted a genome-wide scan on this family seeking genetic linkage. One interval on chromosome 4q gives a peak multipoint LOD score of 2.70 using a strict model that treats only the CVID patients and one obligate carrier with dysgammaglobulinemia as affected. Extending the definition of likely affected to include IgAD boosts the peak multipoint LOD score to 3.38. The linkage interval spans at least from D4S2361 to D4S1572. We extended our study to a collection of 32 families with at least one CVID case and a second case of either CVID or IgAD. We used the same dominant penetrance model and genotyped and analyzed nine markers on 4q. The 32 families have a peak multipoint LOD score under heterogeneity of 0.96 between markers D4S423 and D4S1572 within the suggested linkage interval of the first family, and an estimated proportion of linked families (alpha) of 0.32, supporting the existence of a disease-causing gene for autosomal-dominant CVID/IgAD on chromosome 4q.

Analysis of families with common variable immunodeficiency (CVID) and IgA deficiency suggests linkage of CVID to chromosome 16q

Common variable immunodeficiency (CVID) is an antibody deficiency syndrome that often co-occurs in families with selective IgA deficiency (IgAD). Vorechovský et al. (Am J Hum Genet 64:1096-1109, 1999; J Immunol 164:4408-4416, 2000) ascertained and genotyped 101 multiplex IgAD families and used them to identify and fine map the IGAD1 locus on chromosome 6p. We analyzed the original genotype data in a subset of families with at least one case of CVID and present evidence of a CVID locus on chromosome 16q with autosomal dominant inheritance. The peak (model-based) LOD score for the best marker D16S518 is 2.83 at theta=0.07, and a 4-marker LOD score under heterogeneity peaks at 3.00 with alpha=0.68. The (model-free) NPL score using the same markers peaks at the same location with a value of 3.38 (P=0.0001).

Clinical and immunological features of 65 Iranian patients with common variable immunodeficiency

Common variable immunodeficiency (CVID) is a primary immunodeficiency disease characterized by hypogammaglobulinemia and recurrent bacterial infections. The records of 65 patients with CVID (37 males and 28 females) in the age range of 24 to 537 months were reviewed. By the year 2003, 11 patients had died and seven patients could not be located. The total follow-up period was 221 patient-years. The median diagnostic delay (time between onset and diagnosis) in our patient group was 60 months. At the time of diagnosis, the baseline serum immunoglobulin G (IgG), IgM, and IgA levels were below the level normal for the patients' age; the medians for this group were 120, 10, and 0 mg/dl, respectively. All of the patients presented with infectious diseases at the time of onset, the most common of which were otitis media, diarrhea, pneumonia, and sinusitis. Acute and recurrent infections were also found in almost all of the patients, particularly involving respiratory and gastrointestinal systems. The most common infections, before diagnosis and during follow-up, were pneumonia, acute diarrhea, acute sinusitis, and otitis media. CVID should be considered in any patient with a history of recurrent infections and decreased levels of all serum immunoglobulin isotypes.

The genetics of hypogammaglobulinemia

Etiologies for human hypogammaglobulinemias are diverse and include genetic and nongenetic causes. Although recent reviews focus on the complex genetics of common variable immunodeficiency, in this review, we survey different causes of hypogammaglobulinemias and discuss possible mechanisms.

Symptomatic hypogammaglobulinemia in infancy and childhood - clinical outcome and in vitro immune responses

BACKGROUND

Symptomatic hypogammaglobulinemia in infancy and childhood (SHIC), may be an early manifestation of a primary immunodeficiency or a maturational delay in the normal production of immunoglobulins (Ig). We aimed to evaluate the natural course of SHIC and correlate in vitro lymphoproliferative and secretory responses with recovery of immunoglobulin values and clinical resolution.

METHODS

Children, older than 1 year of age, referred to our specialist clinic because of recurrent infections and serum immunoglobulin (Ig) levels 2 SD below the mean for age, were followed for a period of 8 years. Patient with any known familial, clinical or laboratory evidence of cellular immunodeficiency or other immunodeficiency syndromes were excluded from this cohort. Evaluation at 6- to 12-months intervals continued up to 1 year after resolution of symptoms. In a subgroup of patients, in vitro lymphocyte proliferation and Ig secretion in response to mitogens was performed.

RESULTS

32 children, 24 (75%) males, 8 (25%) females, mean age 3.4 years fulfilled the inclusion criteria.

CLINICAL PRESENTATION

ENT infections 69%, respiratory 81%, diarrhea 12.5%. During follow-up, 17 (53%) normalized serum Ig levels and were diagnosed as transient hypogammaglobulinemia of infancy (THGI). THGI patients did not differ clinically or demographically from non-transient patients, both having a benign clinical outcome. In vitro Ig secretory responses, were lower in hypogammaglobulinemic, compared to normal children and did not normalize concomitantly with serum Ig's in THGI patients.

CONCLUSIONS

The majority of children with SHIC in the first decade of life have THGI. Resolution of symptoms as well as normalization of Ig values may be delayed, but overall the clinical outcome is good and the clinical course benign.

Molecular analysis of B-cell differentiation in selective or partial IgA deficiency

Selective IgA deficiency is the most common form of primary immunodeficiency, the molecular basis of which is unknown. To investigate the cause of selective IgA deficiency, we examined what stage of B-cell differentiation was blocked. DNA and RNA were extracted from three Japanese patients with selective IgA deficiency and three with a partial IgA deficiency. In selective IgA deficiency patients, Ialpha germline transcript expression levels decreased and alpha circle transcripts were not detected. Stimulation with PMA and TGF-beta1 up-regulated Ialpha germline and alpha circle transcripts. In some patients, IgA secretion was induced by stimulation with anti-CD40, IL-4 and IL-10. In partial IgA deficiency patients, Ialpha germline, alpha circle transcripts and Calpha mature transcripts were detected in the absence of stimulation. Our findings suggest that the decreased expression level of Ialpha germline transcripts before a class switch might be critical for the pathogenesis of some patients with selective IgA deficiency. However, in patients with a partial IgA deficiency, B-cell differentiation might be disturbed after a class switch.

The Complex Genetics of Common Variable Immunodeficiency

Immunoglobulin (lg)A deficiency and common variable immunodeficiency (CVID) are the most common primary immunodeficiency disorders in North America and Europe. These diseases appear to comprise a familial spectrum of immunodeficiency that ranges from partial IgA deficiency to a complete absence of serum immunoglobulin. The CVID phenotype is typically acquired and can spontaneously revert to IgG and IgM sufficiency. Family studies suggest the presence of at least two susceptibility loci within the major histocompatibility complex on the short arm of chromosome 6: one located near the class II region and the other located near the junction between the class III and class I regions. Inheritance of these susceptibility genes may yield an additive risk for the development of immunodeficiency. First-degree family members of patients with CVID are at risk throughout their lives for the development of these diseases and should be monitored with a high index of suspicion.

Linkage of autosomal dominant common variable immunodeficiency to chromosome 5p and evidence for locus heterogeneity

Common variable immunodeficiency (CVID, OMIM 240500) and selective immunoglobulin A deficiency (IgAD) are the most frequent primary immunodeficiencies in humans. Of the cases with CVID/IgAD, 20%-25% are familial, but the only previous claims of linkage or association are to the HLA region on chromosome 6p. We report the results of a genome-wide scan in three multiplex families with CVID, IgAD, and dysgammaglobulinemia, where affection is inherited in an autosomal dominant pattern. Two of the families are consistent with linkage to the telomeric region of chromosome 5p, whereas the third is consistent with linkage to the HLA region. Using a locus heterogeneity model and a conservative penetrance model, we obtained a LOD score of 3.35 for the 5p region. We sequenced the exons of one promising candidate gene within this region (PDCD6, also known as ALG-2) but found no causative mutation.

Fine-scale mapping at IGAD1 and genome-wide genetic linkage analysis implicate HLA-DQ/DR as a major susceptibility locus in selective IgA deficiency and common variable immunodeficiency

Selective IgA deficiency (IgAD) and common variable immunodeficiency (CVID) are the most common primary immunodeficiencies in humans. A high degree of familial clustering, marked differences in the population prevalence among ethnic groups, association of IgAD and CVID in families, and a predominant inheritance pattern in multiple-case pedigrees have suggested a strong, shared genetic predisposition. Previous genetic linkage, case-control, and family-based association studies mapped an IgAD/CVID susceptibility locus, designated IGAD1, to the MHC, but its precise location within the MHC has been controversial. We have analyzed a sample of 101 multiple- and 110 single-case families using 36 markers at the IGAD1 candidate region and mapped homozygous stretches across the MHC shared by affected family members. Haplotype analysis, linkage disequilibrium, and homozygosity mapping indicated that HLA-DQ/DR is the major IGAD1 locus, strongly suggesting the autoimmune pathogenesis of IgAD/CVID. This is supported by the highest excess of allelic sharing at 6p in the genome-wide linkage analysis of 101 IgAD/CVID families using 383 marker loci, by previously reported restrictions of the T cell repertoires in CVID, the presence of autoantibodies, impaired T cell activation, and a dysregulation of a number of genes in the targeted immune system. IgAD/CVID may thus provide a useful model for the study of pathogenesis and novel therapeutic strategies in autoimmune diseases.

Analysis of Ig subclass deficiency: First reported case of IgG2, IgG4, and IgA deficiency caused by deletion of C alpha 1, psi C gamma, C gamma 2, C gamma 4, and C epsilon in a Mongoloid patient

BACKGROUND

The cause of Ig class or subclass deficiencies has been unclear except for IgH gene deletions and a homozygous 1-base insertion (1793insG) in C gamma 2 exon 4 of IgG2 deficiency. In addition, there are no reports that IgH gene deletions are found in patients who are Mongoloid (a category that includes most of the people of Asia, such as the Japanese, Chinese, Indonesians and Malaysians).

OBJECTIVE

To investigate the cause of Ig subclass deficiency, we extensively investigated 4 Japanese patients with low serum IgG2 levels. Patient 1 was a 23-month-old girl whose serum IgG2, IgG4, and IgA levels were under the detection limits; she also had idiopathic thrombocytopenic purpura. Patient 2 was a 5-year-old boy whose serum IgG2 level was under the detection limit. Patient 3 was a 14-month-old boy whose serum IgG2 and IgG4 levels were under the detection limits. Patient 4 was 3-year-old girl whose IgG2 level was low and whose IgA level was under the detection limit.

METHODS

DNA was extracted from neutrophils, and Southern blot analysis was performed.

RESULTS

Southern blot analysis revealed that patient 1 had lost the C alpha 1, psi C gamma, C gamma 2, C gamma 4, and C epsilon genes and was a homozygous carrier of the deletion described above. Her mother was of the heterozygous genotype. DNA from patients 2, 3, and 4 revealed no deletions in comparison with control DNA.

CONCLUSION

This is a report of the first case of a Mongoloid in whom IgG2, IgG4, and IgA deficiency was caused by deletion of C alpha 1, psi C gamma, C gamma 2, C gamma 4, and C epsilon. Our finding contributes to investigations of Ig subclass deficiency.

Antibody deficiency syndromes

Antibodies have a crucial role in protecting against infections, and antibody deficiencies are the commonest primary and secondary immunodeficiencies. Antibody deficiencies may be the only abnormality present in a patient, or they may be present and aggravate the symptoms of various other conditions. Because the presence of an antibody deficiency is difficult to predict from clinical presentation, physicians should perform an evaluation of antibody-mediated immunity, even knowing that, in many cases, the results are normal. When immunizations are included as a part of the evaluation, many patients experience a benefit from enhanced immunity against common pathogens. Some alternative practical approaches to the evaluation of patients with recurrent infections are outlined in Figure 8. Referral to a clinical immunologist can be based on the presence of recurrent infections, a positive family history without prior evaluation by a pediatrician, or abnormal immunologic findings that require an advanced evaluation. In any case, a close collaboration between pediatrician and immunologist likely will result in an accurate diagnosis and better treatment of patients with antibody-deficiency syndromes and their families.

A Putative Susceptibility Locus on Chromosome 18 Is Not a Major Contributor to Human Selective IgA Deficiency: Evidence from Meiotic Mapping of 83 Multiple-Case Families

Previous reports of an association between constitutional chromosome 18 abnormalities and low levels of IgA suggested that this chromosome contains a susceptibility locus for selective IgA deficiency (IgAD), the most frequent Ig deficiency in humans. IgAD is genetically related to common variable immunodeficiency (CVID), characterized by a lack of additional isotypes. Our previous linkage analysis of 83 multiple-case IgAD/CVID families containing 449 informative pedigree members showed a significantly increased allele sharing in the chromosome region 6p21 consistent with allelic associations in family-based and case-control studies and provided the evidence for a predisposing locus, termed IGAD1, in the proximal part of the MHC. We have typed the same family material at 17 chromosome 18 marker loci with the average intermarker distance of 7 cM. A total of 7633 genotypes were analyzed in a nonparametric linkage analysis, but none of the marker loci exhibited a significantly increased allele sharing in affected family members. In addition, reverse painting and deletion mapping of a panel of constitutional chromosome 18 deletions/translocations showed the presence of IgA-deficient and IgA-proficient patients with the same abnormality and did not reveal a region commonly deleted. The linkage analysis of chromosome 8 and 21 regions involved in reciprocal translocations t(8;18) and t(18;21), which were identified in two patients lacking IgA, did not disclose a significant allele sharing. Although these results do not exclude the presence of a minor predisposing locus on this chromosome, such a putative locus would confer a population risk of developing IgAD/CVID much lower than IGAD1.

Common variable immunodeficiency: clinical and immunological features of 248 patients

Common variable immunodeficiency (CVI) is a primary immunodeficiency disease characterized by reduced serum immunoglobulins and heterogeneous clinical features. In these studies we describe the clinical and immunological status of 248 consecutively referred CVI patients of age range 3-79 years who have been followed for a period of 1-25 years. The median age at the time of onset of symptoms was 23 years for males and 28 years for females; the mean age at which the diagnosis of CVI was made was 29 years for males and 33 years for females. Forty percent of patients had impaired T cell proliferation to one or more mitogens; lymphocyte transformation to mitogens was directly related to the level of the serum IgG. Females at all ages had higher levels of serum IgM than males. Survival 20 years after diagnosis of CVI was 64% for males and 67% for females, compared to the expected 92% population survival for males and 94% for females. Parameters associated with mortality in this period were lower levels of serum IgG, poorer T cell responses to phytohemagglutinin, and, particularly, a lower percentage of peripheral B cells (P < 0.006).

HLA class II homozygosity confers susceptibility to common variable immunodeficiency (CVID)

Most cases of CVID occur sporadically, but familial cases do also occur and 15% of the patients with the disease have first degree relatives with IgA deficiency (IgAD). Our purpose was to study CVID association with HLA class II alleles and to ascertain whether this disease shares a common genetic background with IgAD in our population. Patients with CVID (n = 42), were typed using gene amplification and sequence-specific oligonucleotide probing for HLA-DRB1, DRB3, DQA1 and DQB1 loci and their typing compared with that of 96 IgAD and 334 healthy controls. We observed a positive association between non-Asp residues at position 57 of the HLA-DQbeta chain and CVID, although much weaker than in IgAD. Further, we found an association between CVID and homozygosity for genes encoding HLA class II molecules, especially HLA-DQ, not seen in IgAD. The data support the hypothesis that a restricted diversity of HLA class II molecules may contribute to susceptibility to CVID.

Genetic linkage of IgA deficiency to the major histocompatibility complex: evidence for allele segregation distortion, parent-of-origin penetrance differences, and the role of anti-IgA antibodies in disease predisposition

Immunoglobulin A (IgA) deficiency (IgAD) is characterized by a defect of terminal lymphocyte differentiation, leading to a lack of IgA in serum and mucosal secretions. Familial clustering, variable population prevalence in different ethnic groups, and a predominant inheritance pattern suggest a strong genetic predisposition to IgAD. The genetic susceptibility to IgAD is shared with a less prevalent, but more profound, defect called "common variable immunodeficiency" (CVID). Here we show an increased allele sharing at 6p21 in affected members of 83 multiplex IgAD/CVID pedigrees and demonstrate, using transmission/diseqilibrium tests, family-based associations indicating the presence of a predisposing locus, designated "IGAD1," in the proximal part of the major histocompatibility complex (MHC). The recurrence risk of IgAD was found to depend on the sex of parents transmitting the defect: affected mothers were more likely to produce offspring with IgAD than were affected fathers. Carrier mothers but not carrier fathers transmitted IGAD1 alleles more frequently to the affected offspring than would be expected under random segregation. The differential parent-of-origin penetrance is proposed to reflect a maternal effect mediated by the production of anti-IgA antibodies tentatively linked to IGAD1. This is supported by higher frequency of anti-IgA-positive females transmitting the disorder to children, in comparison with female IgAD nontransmitters, and by linkage data in the former group. Such pathogenic mechanisms may be shared by other MHC-linked complex traits associated with the production of specific autoantibodies, parental effects, and a particular MHC haplotype.

Primary antibody deficiency in Arabs: first report from eastern Saudi Arabia

Epidemiological studies have shown wide geographical and racial variations in the prevalence and pattern of immunodeficiency diseases. As there is no national registry, very little is known of the prevalence and nature of humoral immunodeficiency in the Arabian peninsula. We report here for the first time the analysis of serum immunoglobulin (Ig) levels in 2000 consecutive patients (age, 1-80 years). They were seen over a period of 6 years and were referred to us from six district hospitals for suspected immunodeficiency, autoimmunity, allergy, or immunoglobulin dyscrasia. Forty-six were found to be immunodeficient, in whom at least one of the Ig class was low; 15 had secondary immunodeficiency. The remaining 31 cases, representing 1.5% of the population studied (giving a prevalence of 1550/100,000 hospital registered patients), were categorized into four primary humoral immunodeficiency groups: these included, in order of frequency, (i) selective IgA deficiency (45%; 700/100,000) (ii) common variable immunodeficiency (CVID) (29%; 450/100,000), (iii) agammaglobulinemia (16%; 250/100,000), and (iv) selective IgG deficiency (10%; 150/100,000). Compared with similar hospital-based surveys in the west the prevalence of humoral immunodeficiency seems to be higher in Arabs; this in part may be related to race and higher rate of consanguinity. Most patients with IgA deficiency had either infection, atopy or autoimmunity. Compared with some other races, agammaglobulinemia (X- and non-X-linked) seems to be more prevalent.

Genetic basis of abnormal B cell development

A susceptibility gene in the MHC class III region may underlie the defective B-cell differentiation in familial IgA deficiency and common variable immunodeficiency. Mutations in Bruton's tyrosine kinase, immunoglobulin heavy chain and lambda 5/14.1 surrogate light chain loci disrupt B-cell development to cause profound antibody deficiency. Mutational, biochemical and transgenic studies offer insight into the function of these and other 'antibody deficiency genes'.

Susceptibility locus for IgA deficiency and common variable immunodeficiency in the HLA-DR3, -B8, -A1 haplotypes

BACKGROUND

A common genetic basis for IgA deficiency (IgAD) and common variable immunodeficiency (CVID) is suggested by their occurrence in members of the same family and the similarity of the underlying B cell differentiation defects. An association between IgAD/CVID and HLA alleles DR3, B8, and A1 has also been documented. In a search for the gene(s) in the major histocompatibility complex (MHC) that predispose to IgAD/CVID, we analyzed the extended MHC haplotypes present in a large family with 8 affected members.

MATERIALS AND METHODS

We examined the CVID proband, 72 immediate relatives, and 21 spouses, and determined their serum immunoglobulin concentrations. The MHC haplotype analysis of individual family members employed 21 allelic DNA and protein markers, including seven newly available microsatellite markers.

RESULTS

Forty-one (56%) of the 73 relatives by common descent were heterozygous and nine (12%) were homozygous for a fragment or the entire extended MHC haplotype designated haplotype 1 that included HLA- DR3, -C4A-0, -B8, and -A1. The remarkable prevalence of haplotype 1 was due in part to marital introduction into the family of 11 different copies of the haplotype, eight sharing 20 identical genotype markers between HLA-DR3 and HLA-B8, and three that contained fragments of haplotype 1.

CONCLUSION

Crossover events within the MHC indicated a susceptibility locus for IgAD/CVID between the class III markers D821/D823 and HLA-B8, a region populated by 21 genes that include tumor necrosis factor alpha and lymphotoxins alpha and beta. Inheritance of at least this fragment of haplotype 1 appears to be necessary for the development of IgAD/CVID in this family.