Assessment of male CVID patients for mutations in the Btk gene: how many have been misdiagnosed?

Acute primary purulent pericarditis in an adult patient with unknown X-linked agammaglobulinemia

X-linked agammaglobulinemia (XLA) is a rare form of inherited immunodeficiency due to an impairment in B-lymphocyte differentiation and maturation. In the majority of cases XLA is diagnosed in childhood, particularly among males affected by recurrent infections and with a family history of immunodeficiency. Infections of respiratory tract, gastrointestinal apparatus, eyes, nose and ears are frequent in XLA patients; on the contrary, infections of myocardium, cardiac valves and pericardium are rarely described in XLA. A 34-year-old man with unknown XLA was hospitalized because of syncope, due to pericardial tamponade, caused by acute primary purulent pericarditis. Immediate pericardiocentesis was effective in improving hemodynamics, and empiric antibiotic therapy was successful in controlling the infection. Purulent pericarditis is a rare disease with high mortality rate: it is usually caused by hematogenous bacterial propagation, direct infection of pericardial space by chest wounds or thoracic surgery, or extension of infection from adjacent tissues. However, this patient had no recent local or systemic infections. Because of unusual clinical picture during hospitalization he underwent further clinical and laboratory evaluations, that showed low immunoglobulin levels. After exclusion of acquired immunodeficiency, genetic tests were performed: they detected deletion of exons 8-9-10 of Bruton Tyrosine Kinase gene on X chromosome, leading to the diagnosis of XLA. Acute purulent primary pericarditis may also occur in adult XLA patients as first clinical manifestation. According to this case report, a primary immunodeficiency syndrome should be considered in patients with atypical cardiac infections and no predisposing conditions, regardless of age.

A Novel de Novo Mutation in the CD40 Ligand Gene in a Patient With a Mild X-Linked Hyper-IgM Phenotype Initially Diagnosed as CVID: New Aspects of Old Diseases

Mutations in the CD40 ligand (CD40L) gene (CD40LG) lead to X-linked hyper-IgM syndrome (X-HIGM), which is a primary immunodeficiency (PID) characterized by decreased serum levels of IgG and IgA and normal or elevated IgM levels. Although most X-HIGM patients become symptomatic during the first or second year of life, during which they exhibit recurrent infections, some patients exhibit mild phenotypes, which are usually associated with hypomorphic mutations that do not abrogate protein expression or function. Here, we describe a 28-year-old man who initially presented with recurrent infections since the age of 7 years, when he exhibited meningitis caused by Cryptococcus neoformans. The patient had no family history of immunodeficiency, and based on clinical and laboratory presentation, he was initially diagnosed with common variable immunodeficiency (CVID). In subsequent years, he displayed several sporadic episodes of infection, including pneumonia, pharyngotonsillitis, acute otitis media, rhinosinusitis, fungal dermatosis, and intestinal helminthiasis. The evaluation of CD40L expression on the surface of activated CD3⁺CD4⁺ T cells from the patient showed decreased expression of CD40L. Genetic analysis revealed a novel de novo mutation consisting of a 6-nucleotide insertion in exon 1 of CD40LG, which confirmed the diagnosis of X-HIGM. In this report, we describe a novel mutation in the CD40L gene and highlight the complexities of PID diagnosis in light of atypical phenotypes and hypomorphic mutations as well as the importance of the differential diagnosis of PIDs.

Lymphocytes and B-cell abnormalities in patients with common variable immunodeficiency (CVID)

BACKGROUND AND AIMS

Common variable immunodeficiency (CVID) is a primary antibody deficiency characterised by decreased antibody production and low or normal B-cell numbers. To elucidate the clinical and immunological heterogeneity of CVID, we studied 16 patients diagnosed with CVID.

METHODS

We analysed B, T and NK cell populations. We also assessed CD27 expression to define B-cell subsets and examined the expression of molecules important in B-cell proliferation and differentiation, such as the transmembrane activator and CALM interactor (TACI), inducible costimulator (ICOS), CD154 and CD40.

RESULTS

We observed reduced B and T-cell numbers in CVID patients; this reduction was more pronounced in adults. While one group of patients (group I) showed a significant reduction in CD27+ memory B-cells, another group (group II) of patients exhibited numbers of CD27+ memory B-cells similar to the healthy donor. The frequency of B-cells and T-cells expressing CD40 and ICOS, respectively, was significantly lower in all CVID patients compared with healthy donors. Finally, a correlation between the frequency of CD27+ memory B-cells and clinical features was observed in CVID patients.

CONCLUSION

These results suggest that in some patients, the combined defects in both T and B-cells may account for CVID. Additionally, patients in group I exhibited an increased frequency of pneumonia and chronic diarrhoea.

Adult-onset presentations of genetic immunodeficiencies: genes can throw slow curves

PURPOSE OF REVIEW

The molecular and genetic mechanisms behind adult presentations of primary immunodeficiency diseases are examined, with particular emphasis on cases where this was heralded by severe, recurrent, or opportunistic infection.

RECENT FINDINGS

A detailed analysis over the last two decades of the relationship between genotype and clinical phenotype for a number of genetic immunodeficiencies has revealed multiple mechanisms that can account for the delayed presentation of genetic disorders that typically present in childhood, including hypomorphic gene mutations and X-linked gene mutations with age-related skewing in random X-chromosome inactivation. Adult-onset presentations of chronic granulomatous disease, X-linked agammaglobulinemia, IL-12/Th1/IFN-gamma and IL-23/Th17/IL-17 pathway defects, and X-linked lymphoproliferative disorder are used to illustrate these mechanisms. Finally, certain genetic types of common variable immunodeficiency are used to illustrate that inherited null mutations can take decades to manifest immunologically.

SUMMARY

Both genetic mechanisms and environmental factors can account for adult-onset infectious and noninfectious complications as manifestations of disorders that are typically present in childhood. This emphasizes the potential complexity in the relationship between genotype and phenotype with natural human mutations.

Children with frequent infections: a proposal for a stepwise assessment and investigation of the immune system

Although many children develop frequent infections, only a few have an underlying immune disorder. Children with dysfunction of the immune system develop frequent infections and/or recurrent, persistent, severe, and rare infections. The aim of this review is to provide to the clinician a valuable tool for recognizing any 'discords' of the 'immune-system symphonic orchestra'. By following a reverse route, it will be possible to brighten up the dark and winding road of immunodeficiencies and identify the exact point of immune dysfunction. This is fundamental and crucial to perceive etiologic management and subsequently achieve the best for these young patients and their families.

B-cell activating factor receptor deficiency is associated with an adult-onset antibody deficiency syndrome in humans

B-cell survival depends on signals induced by B-cell activating factor (BAFF) binding to its receptor (BAFF-R). In mice, mutations in BAFF or BAFF-R cause B-cell lymphopenia and antibody deficiency. Analyzing BAFF-R expression and BAFF-binding to B cells in common variable immunodeficiency (CVID) patients, we identified two siblings carrying a homozygous deletion in the BAFF-R gene. Removing most of the BAFF-R transmembrane part, the deletion precludes BAFF-R expression. Without BAFF-R, B-cell development is arrested at the stage of transitional B cells and the numbers of all subsequent B-cell stages are severely reduced. Both siblings have lower IgG and IgM serum levels but, unlike most CVID patients, normal IgA concentrations. They also did not mount a T-independent immune response against pneumococcal cell wall polysaccharides but only one BAFF-R-deficient sibling developed recurrent infections. Therefore, deletion of the BAFF-R gene in humans causes a characteristic immunological phenotype but it does not necessarily lead to a clinically manifest immunodeficiency.

Common variable immunodeficiency: etiological and treatment issues

One of the great advances in clinical medicine was the recognition of the pleomorphism of the immune response and the multiple afferent and efferent limbs of antigen processing and responsiveness. A significant contribution to this understanding was derived from studies of human immunodeficiency states, including both inherited and acquired syndromes. Amongst these syndromes, one of the most common, and least understood, is common variable immune deficiency (CVID). CVID is a syndrome that leads to a reduction in serum immunoglobulins and complications including recurrent infections. Management includes immunoglobulin replacement therapy; however, patients with CVID are at risk for complications of exogenous immunoglobulin administration as well as CVID-associated diseases such as autoimmune processes and malignancies. To assess the current state of knowledge in the field, we performed a literature review of a total of 753 publications covering the period of 1968 until 2008. From this list, 189 publications were selected for discussion. In this review, we demonstrate that while the molecular basis of CVID in many cases remains incompletely understood, significant strides have been made and it is now clear that there is involvement of several pathways of immune activation, with contributions from both T and B cells. Furthermore, despite the current gaps in our knowledge of the molecular pathogenesis of the syndrome, there have been dramatic advances in management that have led to improved survival and significantly reduced morbidity in affected patients.

Common variable immunodeficiency: 20-yr experience at a single centre

Common variable immunodeficiency (CVID) is the most common symptomatic primary immunodeficiency. It can present at any age in patients with a history of recurrent bacterial infections, with or without a family history of other primary immunodeficiencies (PID), and shows a wide range of clinical manifestations and immunological data. Diagnosis is based on low IgG, IgM and/or IgA levels. Delayed diagnosis and therapy can lead to bronchiectasis and malabsorption. The aim of this study was to describe a paediatric population diagnosed of CVID and its evolution in the population. Memory B-cell (MB) classification carried out in these patients was correlated with clinical manifestations and outcome. Clinical and immunological data of 22 CVID children under 18 yr treated at our centre between 1985 and 2005 are presented. Immunological studies included those for diagnosis and MB quantification. Differences in form of presentation, familial incidence and MB classification were reviewed. A statistical descriptive analysis was made. Infections were the commonest manifestation, affecting mainly respiratory (19/22) and gastrointestinal (10/22) tracts. Bronchiectasis was present in seven cases, and detected prior to CVID diagnosis in five. Replacement therapy led to a significant reduction in the number of infections. Severe complications appeared mostly in patients without MB. Patients of the same family share the same MB group. Family members had also been diagnosed of CVID in seven cases. Early diagnosis and therapy are essential to improve outcome in these patients. MB studies are useful in children to orient prognosis and further genetic studies.

Common variable immunodeficiency: a new look at an old disease

Primary immunodeficiencies comprise many diseases caused by genetic defects primarily affecting the immune system. About 150 such diseases have been identified with more than 120 associated genetic defects. Although primary immunodeficiencies are quite rare in incidence, the prevalence can range from one in 500 to one in 500 000 in the general population, depending on the diagnostic skills and medical resources available in different countries. Common variable immunodeficiency (CVID) is the primary immunodeficiency most commonly encountered in clinical practice, and appropriate diagnosis and management of patients will have a significant effect on morbidity and mortality as well as financial aspects of health care. Advances in diagnostic laboratory methods, including B-cell subset analysis and genetic testing, coupled with new insights into the molecular basis of immune dysfunction in some patients with CVID, have enabled advances in the clinical classification of this heterogeneous disease.

TACI, isotype switching, CVID and IgAD

Common Variable Immunodeficiency (CVID) is the most prevalent human primary immunodeficiency requiring medical attention. Until recently the only known genetic defect specific to CVID was ICOS deficiency that accounts for about 1% of the patients analyzed. Mutations in the TNFR family member TACI (transmembrane activator and calcium-modulator and cyclophilin ligand interactor), which mediates isotype switching in B cells, were found to be present in 5% of patients with CVID. Mutations in TACI were also found in relatives of patients with CVID who suffered from IgA deficiency (IgAD) as well as in a patient with isolated IgAD. In the majority of patients described to date only one TACI allele is mutated, showing an autosomal dominant transmission of the disease. B cells from individuals with TACI mutations did not produce IgG and IgA in response to the TACI ligand, APRIL (a proliferation-inducing ligand), probably reflecting impaired isotype switching. These results suggest that TACI mutations can lead to CVID.

Novel mutations in a Japanese patient with CD19 deficiency

Common variable immunodeficiency (CVID) is a heterogeneous disorder characterized by recurrent bacterial infections, hypogammaglobulinemia and low to normal numbers of circulating B cells. Mutations in the ICOS, TACI and CD19 genes have recently been identified in <10% of CVID patients. We, herein, describe two novel CD19 gene disruptions in an 8-year-old Japanese boy, who had been clinically diagnosed as having CVID at the age of 5 years. Flow-cytometric analysis demonstrated absence of CD19 and reduced CD21 expression on CD20-postive peripheral blood B cells. Mutation analysis of CD19 revealed a mutation in the splice acceptor site of intron 5 (IVS5-1G>T) of the maternal allele, resulting in skipping of exon 6, and a truncated protein product. The paternal allele was disrupted by a gross deletion encompassing at least the ATP2A1, CD19 and NFATC2IP genes. The patient had a small number of IgD(-) CD27(+) memory B cells, in which somatic mutation were detected. His B cells showed substantial proliferation upon stimulation, but reduced IgG and IgA production in vitro. These findings extend the mutation spectrum of the CD19 deficiency to four, and confirm the homogeneity of the CD19 deficiency as a unique type 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.

Translational mini-review series on immunodeficiency: molecular defects in common variable immunodeficiency

Common variable immunodeficiency (CVID) is a primary immunodeficiency that typically affects adults and is characterized by abnormalities of quantative and qualitative humoral function that are heterogeneous in their immunological profile and clinical manifestations. The recent identification of four monogenic defects that result in the CVID phenotype also demonstrates that the genetic basis of CVID is highly variable. Mutations in the genes encoding the tumour necrosis factor (TNF) superfamily receptors transmembrane activator and calcium-modulating ligand interactor (TACI) and B cell activation factor of the TNF family receptor (BAFF-R), CD19 and the co-stimulatory molecule inducible co-stimulator molecule (ICOS) all lead to CVID and illustrate the complex interplay required to co-ordinate an effective humoral immune response. The molecular mechanisms leading to the immune defect are still not understood clearly and particularly in the case of TACI, where a number of heterozygous mutations have been found in affected individuals, the molecular pathogenesis of disease requires further elucidation. Together these defects account for perhaps 10-15% of all cases of CVID and it is highly likely that further genetic defects will be identified.

Characterization of novel Bruton's tyrosine kinase gene mutations in Central European patients with agammaglobulinemia

X-linked agammaglobulinemia (XLA) is an immunodeficiency disorder caused by mutations in the gene coding for Bruton's tyrosine kinase (BTK). In this study we investigated 10 male patients with XLA-compatible phenotype (agammaglobulinemia and undetectable B cells in peripheral blood) from 9 unrelated Central European families. We identified seven different mutations, six of which were novel. One previously described point mutation caused a premature stop codon (p.C464X), two point mutations resulted in amino acid exchanges (p.W588R; p.G419E), and two point mutations affected splice sites (c.305-1G>A; c.391+1G>A). We further detected one deletion (c.1921_1927del CGTCCCA) and one large duplication. The duplication resulted from Alu element-induced unequal homologous recombination, which was only detectable by extended analysis of cDNA, while direct sequencing of genomic DNA gave a false negative result. Western blot analysis revealed that the patients with the p.W588R and the p.G419E amino acid substitutions, respectively, produced full length BTK, but in clearly diminished amounts. The patient with the 7bp deletion expressed low amounts of protein which might represent truncated BTK. All other genomic alterations resulted in complete loss of BTK protein. In two patients from unrelated families BTK protein expression was normal and no Btk gene mutation was detected. The results of this study further substantiate the importance of using elaborate molecular analysis with different detection techniques to obtain an explicit molecular diagnosis in patients with suspected XLA.

TACI mutation in common variable immunodeficiency and IgA deficiency

Common variable immunodeficiency (CVID) is a heterogeneous primary immunodeficiency disease. Immunoglobulin A deficiency (IGAD) shares some clinical, laboratory, and genetic features with CVID and occurs with relatively greater frequency in first-degree relatives of individuals with CVID. Recently, patients with CVID and IGAD have been found to have mutations of the gene TNFRSF13B encoding the TACI (transmembrane activator and calcium-modulator and cyclophilin-ligand interactor), a member of the tumor necrosis factor-receptor superfamily. In this article, we review the various TACI mutations that have been identified so far. Although six mutations have been reported, no clear genotype-phenotype association has been shown to date. This suggests that the phenotypic expression of TACI mutation is affected by additional genetic and environmental factors. Analysis of a larger sample of patients will be needed to determine if the specific mutations are associated with a particular phenotype or predisposition to the common features of CVID and IGAD: autoimmunity, lymphoproliferation, or malignancy.

Common variable immunodeficiency: The power of co-stimulation

Common variable immunodeficiency (CVID) is the most frequent symptomatic primary immune deficiency in adults. CVID is characterized by the sequelae of an antibody deficiency syndrome: an impaired terminal B cell differentiation results in hypogammaglobulinemia and susceptibility to recurrent infections by encapsulated bacteria. The clinical course of CVID is complicated by a plethora of systemic immunopathology, including autoimmunity, lymphoproliferation, malignancy and sarcoid-like granulomas. Phenotypic and functional studies in CVID patients revealed multiple abnormalities within the innate and adaptive immune system. The recent description of monogenic defects in ICOS, TACI and CD19 focussed our interest to an impaired T cell-B cell collaboration within the germinal center and intrinsic B cell defects as possible explanations for the etiology of CVID.

Tackling the heterogeneity of CVID

PURPOSE OF REVIEW

Common variable immunodeficiency is clinically the most relevant primary immunodeficiency of the adult. Its heterogeneity has hindered progress in the pathogenetic understanding of the majority of common variable immunodeficiency patients. This abstract summarizes recent aspects of the field and emphasizes the need for a commonly accepted approach to classify common variable immunodeficiency.

RECENT FINDINGS

In the last 2 years, the first genetic defects underlying common variable immunodeficiency, including ICOS, TACI, BAFF-R and CD19, have been identified. The analysis of dendritic cells demonstrated alterations in a majority of patients in addition to the disturbed T and B-cell function. Several changes of the adaptive immune system might be secondary to an underlying chronic inflammatory setting possibly due to a HHV8 infection in a subgroup of patients with granulomatous disease, autoimmune phenomena and T-cell dysfunction. The occurrence of granulomatous inflammation is associated with a worse prognosis compared with common variable immunodeficiency patients without granuloma.

SUMMARY

The pathogenesis of common variable immunodeficiency includes disturbances of the adaptive as well as innate immune system. Identified monogenic defects account for about 10% of cases, leaving the majority of defects undefined and certainly in part epigenetic. To combine the known aspects of the pathogenesis of common variable immunodeficiency to a conclusive picture, the clinical and immunologic phenotyping of patients needs to be standardized.

TACI is mutant in common variable immunodeficiency and IgA deficiency

The tumor necrosis factor receptor family member TACI (transmembrane activator and calcium-modulator and cyclophilin ligand interactor) mediates isotype switching in B cells. We found that 4 of 19 unrelated individuals with common variable immunodeficiency (CVID) and 1 of 16 individuals with IgA deficiency (IgAD) had a missense mutation in one allele of TNFRSF13B (encoding TACI). One of the four individuals with CVID had a single nucleotide insertion in the other TNFRSF13B allele. None of these mutations were present in 50 healthy subjects. TNFRSF13B mutations cosegregated with the phenotype of CVID or IgAD in family members of four index individuals that we studied. B cells from individuals with TACI mutations expressed TACI but did not produce IgG and IgA in response to the TACI ligand APRIL, probably reflecting impaired isotype switching. These results suggest that TACI mutations can result in CVID and IgAD.

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.

XLA patients with BTK splice-site mutations produce low levels of wild-type BTK transcripts

X-linked agammaglobulinemia is caused by mutations in the BTK gene, which result in a precursor B-cell differentiation arrest in the bone marrow and the absence of or strongly reduced B lymphocytes in blood. We identified a patient with a mild clinical phenotype, low numbers of B lymphocytes, and a splice-site mutation in the BTK gene. The precursor B-cell compartment in the bone marrow of this patient was almost identical to that in healthy children. Using real-time quantitative polymerase chain reaction, we were able to detect low levels of wild-type BTK transcripts in his granulocytes. Therefore, we speculated that wild-type BTK transcripts might be responsible for a milder clinical and immunological phenotype, as has been shown in several other diseases. Consequently, we quantified the expression of wild-type BTK transcripts in granulocytes of eight additional patients with splice-site mutations and compared their phenotypes with 17 patients with other types of BTK mutations. In these eight patients, the presence of low levels of wild-type BTK transcripts did not show a clear correlation with the percentage, absolute number, or immunophenotype of B lymphocytes nor with age or serum immunoglobulin levels at diagnosis. Nevertheless, we postulate that the presence of wild-type BTK transcripts can be one of the many factors that influence the clinical and immunological phenotype in X-linked agammaglobulinemia.