Clinical characteristics.

X-linked agammaglobulinemia (XLA) is characterized by recurrent bacterial infections in affected males in the first two years of life. Recurrent otitis is the most common infection prior to diagnosis. Conjunctivitis, sinopulmonary infections, diarrhea, and skin infections are also frequently seen. Approximately 60% of individuals with XLA are recognized as having immunodeficiency when they develop a severe, life-threatening infection such as pneumonia, empyema, meningitis, sepsis, cellulitis, or septic arthritis. S pneumoniae and H influenzae are the most common organisms found prior to diagnosis and may continue to cause sinusitis and otitis after diagnosis and the initiation of gammaglobulin substitution therapy. Severe, difficult-to-treat enteroviral infections (often manifest as dermatomyositis or chronic meningoencephalitis) can be prevented by this treatment. The prognosis for individuals with XLA has improved markedly in the last 25 years as a result of earlier diagnosis, the development of preparations of gammaglobulin that allow normal concentrations of serum IgG to be achieved, and more liberal use of antibiotics.

Diagnosis/testing.

The diagnosis of XLA is suspected in males with early-onset bacterial infections, marked reduction in all classes of serum immunoglobulins, and absent B cells (CD19+ cells); the decrease in the number of B cells is the most consistent and distinctive feature. Adenoids and tonsils are frequently rudimentary and lymph nodes are reduced in size. Having a maternal uncle or male cousin with absent B cells makes the diagnosis almost certain. The diagnosis is established (or confirmed) in males who have a hemizygous BTK pathogenic variant and females who have a heterozygous BTK pathogenic variant.

Management.

Treatment of manifestations: The mainstay of treatment is gammaglobulin substitution therapy (by weekly subcutaneous injection or intravenous infusion every 2-4 weeks) to prevent bacterial infections; some centers use chronic prophylactic antibiotics to prevent infections.

Prevention of secondary complications: The most common secondary complications of XLA are chronic sinusitis, chronic lung disease, inflammatory bowel disease, and enteroviral infection. Generous use of antibiotics can decrease the incidence of chronic sinusitis and lung disease. Diagnosis and treatment of bowel infections may decrease the risk of inflammatory bowel disease.

Agents/circumstances to avoid: Live viral vaccines, particularly oral polio vaccine; inactivated polio vaccine rather than live oral polio vaccine should be given to patients and their family contacts.

Evaluation of relatives at risk: Molecular genetic testing of at-risk male relatives as soon after birth as possible ensures that gammaglobulin substitution therapy is initiated as soon as possible in affected individuals.

Genetic counseling.

XLA is inherited in an X-linked manner. The risk to the sibs depends on the carrier status of the mother: if the mother is heterozygous for a BTK pathogenic variant, there is a 50% chance of transmitting the BTK pathogenic variant in each pregnancy; males who inherit the pathogenic variant will be affected; females who inherit the pathogenic variant will be carriers. All daughters of a male proband will inherit the BTK pathogenic variant and will be carriers; sons are not affected. Once the BTK pathogenic variant has been identified in an affected family member, carrier testing for at-risk females is possible and prenatal testing for a pregnancy at increased risk and preimplantation genetic testing are possible options.

Suggestive Findings

X-linked agammaglobulinemia (XLA) should be suspected in an individual with the following clinical history, laboratory findings, and family history.

Clinical history. Any of the following:

• Recurrent otitis, pneumonitis, sinusitis, and conjunctivitis starting before age five years
• A severe life-threatening bacterial infection such as sepsis, meningitis, cellulitis, or empyema
• Paucity of lymphoid tissue (small adenoids, tonsils, and lymph nodes on physical examination)

Laboratory findings

• Marked reduction in all classes of serum immunoglobulins [Lederman & Winkelstein 1985, Conley et al 2005]
  • The serum IgG concentration is typically <200 mg/dL (2 g/L). Most but not all individuals with XLA do have some measurable serum IgG, usually between 100 and 200 mg/dL, and ~10% of individuals have serum concentration of IgG >200 mg/dL.
  • The serum concentrations of IgM and IgA are typically <20 mg/dL. Particular attention should be given to serum IgM concentration. Although decreased serum concentration of IgG and IgA can be seen in children with a constitutional delay in immunoglobulin production, low serum IgM concentration is almost always associated with immunodeficiency.
• Markedly reduced numbers of B lymphocytes (CD 19+ cells) in the peripheral circulation (<1%) [Conley 1985, Nonoyama et al 1998]
• Antibody titers to vaccine antigens. Individuals with XLA fail to make antibodies to vaccine antigens like tetanus, H influenzae, or S pneumoniae.
• Severe neutropenia in ~10%-25% of individuals at the time of diagnosis, usually in association with pseudomonas or staphylococcal sepsis [Conley & Howard 2002]

Family history of immunodeficiency consistent with X-linked inheritance

Establishing the Diagnosis

Male proband. The diagnosis of XLA is established in a male proband with suggestive clinical and laboratory findings and a hemizygous pathogenic variant in BTK identified by molecular genetic testing (see Table 1).

Molecular genetic testing approaches can include single-gene testing, use of a multigene panel, and more comprehensive genomic testing:

• Single-gene testing. Sequence analysis of BTK is performed first followed by gene-targeted deletion/duplication analysis if no pathogenic variant is found.
  Note: (1) Because approximately 3%-5% of individuals with a BTK pathogenic variant have large deletions that include all or part of BTK and the closely linked gene TIMM8A (also called DDP) resulting in XLA and deafness-dystonia-optic neuropathy syndrome (DDON; also called Mohr-Tranebjærg syndrome) [Richter et al 2001, Sedivá et al 2007], additional testing with chromosomal microarray analysis (CMA) may be warranted. (2) For individuals with clinical features of XLA and DDON, consider CMA testing first.
• A multigene panel that includes BTK and other genes of interest (see Differential Diagnosis) may also be considered. Note: (1) The genes included in the panel and the diagnostic sensitivity of the testing used for each gene vary by laboratory and are likely to change over time. (2) Some multigene panels may include genes not associated with the condition discussed in this GeneReview; thus, clinicians need to determine which multigene panel is most likely to identify the genetic cause of the condition while limiting identification of variants of uncertain significance and pathogenic variants in genes that do not explain the underlying phenotype. (3) In some laboratories, panel options may include a custom laboratory-designed panel and/or custom phenotype-focused exome analysis that includes genes specified by the clinician. (4) Methods used in a panel may include sequence analysis, deletion/duplication analysis, and/or other non-sequencing-based tests.
  For an introduction to multigene panels click here. More detailed information for clinicians ordering genetic tests can be found here.
• More comprehensive genomic testing (when available) including exome sequencing and genome sequencing may be considered if serial single-gene testing (and/or use of a multigene panel that includes BTK) fails to confirm a diagnosis in an individual with features of XLA. Such testing may also provide or suggest a diagnosis not previously considered (e.g., mutation of a different gene or genes that results in a similar clinical presentation).
  For an introduction to comprehensive genomic testing click here. More detailed information for clinicians ordering genomic testing can be found here.

Clinical Description

Males with X-linked agammaglobulinemia (XLA) are usually well for the first few months of life because they are protected by transplacentally acquired maternal immunoglobulin. Typically, affected males develop recurrent bacterial infections in the first two years of life and are recognized as having immunodeficiency before age five years [Ochs & Smith 1996, Conley & Howard 2002, Plebani et al 2002, Winkelstein et al 2006].

Recurrent otitis is the most common infection prior to diagnosis. Conjunctivitis, sinopulmonary infections, diarrhea, and skin infections are also frequently seen. Approximately 60% of individuals with XLA are recognized as having immunodeficiency when they develop a severe, life-threatening infection such as pneumonia, empyema, meningitis, sepsis, cellulitis, or septic arthritis. Because males with XLA fail to make antibodies to vaccine antigens like tetanus, H influenzae, or S pneumoniae, the latter two organisms are the most commonly seen prior to diagnosis of XLA and they may continue to cause sinusitis and otitis even after diagnosis and the initiation of gammaglobulin substitution therapy [Lederman & Winkelstein 1985, Conley et al 2005].

Individuals with XLA are not vulnerable to the majority of viral infections; however, they are susceptible to severe and chronic enteroviral infections (often manifesting as dermatomyositis or chronic meningoencephalitis) [Wilfert et al 1977, Bearden et al 2016]. In the past, 5%-10% of individuals with XLA developed vaccine-associated polio after vaccination with the live attenuated oral polio vaccine. Since the mid-1980s, when gammaglobulin substitution therapy became available, the incidence of chronic enteroviral infection has markedly decreased in individuals with XLA. However, some individuals still develop enteroviral encephalitis and some have neurologic deterioration of unknown etiology [Misbah et al 1992, Ziegner et al 2002].

Like all individuals with antibody deficiencies, persons with XLA are highly susceptible to giardia infection. They may also develop persistent mycoplasma infections. Infections with unusual organisms, like Flexispira or Helicobacter cinaedi, may also be troublesome [Cuccherini et al 2000, Simons et al 2004].

Approximately 10% of males with a hemizygous BTK pathogenic variant are not recognized as having immunodeficiency until after age ten years and some not until adulthood [Howard et al 2006, Conley et al 2008]. Some affected males have higher serum immunoglobulin concentrations than expected, but all have very low numbers of B cells.

The prognosis for individuals with XLA has improved markedly in the last 35 years [Howard et al 2006] as a result of earlier diagnosis, more liberal use of antibiotics, and the development of preparations of gammaglobulin that allow gammaglobulin substitution therapy to achieve normal concentrations of serum IgG. Most individuals lead a normal life. However, approximately 10% develop significant infections despite appropriate therapy and many have chronic pulmonary changes [Quartier et al 1999].

Heterozygous females. A single female with XLA has been reported. Her father had XLA and analysis demonstrated exclusive use of the paternally derived X chromosome as the active X [Takada et al 2004].

Genotype-Phenotype Correlations

No strong correlation is observed between the specific BTK pathogenic variant and the severity of disease; however, individuals who have amino acid substitutions or splice defects that occur at sites that are conserved, but not invariant, tend to be older at the time of diagnosis, and have higher serum concentrations of IgM and slightly more B cells in the peripheral circulation [López-Granados et al 2005, Broides et al 2006].

Nomenclature

Bruton called the disorder that he first described in 1952 "agammaglobulinemia." The X-linked pattern of inheritance was noted shortly after that time.

In the 50s, 60s, and 70s, the disorder was sometimes called congenital agammaglobulinemia, familial hypogammaglobulinemia or infantile agammaglobulinemia, or simply agammaglobulinemia.

Prevalence

Prevalence of X-linked agammaglobulinemia is approximately 3:1,000,000-6:1,000,000 males in all racial and ethnic groups.

Evaluations Following Initial Diagnosis

To establish the extent of disease and needs of an individual diagnosed with X-linked agammaglobulinemia (XLA), the following evaluations are recommended:

• A complete blood count with differential
• Chemistries that include renal and liver function tests, total protein, albumin, and CRP
• Quantitative serum immunoglobulins and titers to vaccine antigens as baseline measurements prior to initiation of gammaglobulin substitution therapy
• Baseline chest and sinus x-rays
• If the patient is able to cooperate, base line pulmonary function tests
• Consultation with a clinical geneticist and/or genetic counselor

Treatment of Manifestations

Individuals with XLA should receive specialty care at a center with expertise in this disorder.

If individuals develop acute infections, they should be treated with a course of antibiotics that is at least twice as long as that used in otherwise healthy individuals. Generous use of antibiotics is recommended and treatment should be given without any unnecessary delay.

Prevention of Primary Manifestations

Prevention of Secondary Complications

Children with XLA should only be given inactivated polio vaccine (IPV) and not oral polio vaccine.

The sibs of children with XLA should also be given IPV rather than oral polio vaccine (in order to avoid infecting their affected sib with live virus).

Surveillance

At least once a year:

• A complete blood count with differential, chemistries, and quantitative serum immunoglobulins to monitor gammaglobulin substitution therapy
• Chest x-rays or CTs and sinus films
  Note: Chronic lung disease can develop in the absence of an acute pulmonary infection [Quartier et al 1999].

If the patient is stable, the serum IgG does not need to be evaluated with every infusion of gammaglobulin.

Agents/Circumstances to Avoid

Live viral vaccines, particularly oral polio vaccine, should be avoided in individuals with XLA.

Evaluation of Relatives at Risk

It is appropriate to evaluate at-risk male relatives as soon after birth as possible so that gammaglobulin substitution therapy can be initiated promptly and administration of live viral vaccines can be avoided. Evaluations can include:

• Molecular genetic testing for the known family-specific BTK pathogenic variant;
• Analysis of the percentage of B cells in the peripheral circulation.

Note: Serum immunoglobulins will not be helpful in the evaluation of a newborn or infant because maternal IgG crosses the placenta.

See Genetic Counseling for issues related to testing of at-risk relatives for genetic counseling purposes.

Therapies Under Investigation

Research studies exploring gene therapy for XLA have been conducted in mice [Kerns et al 2010, Ng et al 2010, Bestas et al 2014], but it is not clear when this type of treatment may be available for humans.

Search ClinicalTrials.gov in the US and EU Clinical Trials Register in Europe for access to information on clinical studies for a wide range of diseases and conditions.

Mode of Inheritance

X-linked agammaglobulinemia is inherited in an X-linked manner.

Risk to Family Members

Parents of a proband

• The father of an affected male will not have the disorder nor will he be hemizygous for the BTK pathogenic variant; therefore, he does not require further evaluation/testing.
• In a family with more than one affected individual, the mother of an affected male is an obligate heterozygote (carrier).
• If a woman has more than one affected child and no other affected relatives and if the BTK pathogenic variant cannot be detected in her leukocyte DNA, she has germline mosaicism. Germline mosaicism has been observed [Sakamoto et al 2001].
• If an affected male is the only affected family member (50% of affected males represent simplex cases), there are two possibilities:
  • The mother is a carrier (~80%-85% of cases).
  • The affected male has a de novo pathogenic variant, in which case the mother is not a carrier (~15%-20% of cases)

Sibs of a proband

• The risk to sibs depends on the genetic status of the mother.
• If the mother is a carrier, the chance of transmitting the pathogenic variant in each pregnancy is 50%. Males who inherit the pathogenic variant will be affected; females who inherit the pathogenic variant will be carriers and are highly unlikely to be affected.
• Germline mosaicism has been observed [Sakamoto et al 2001]. Thus, if an affected male represents a single case in a family and if the BTK pathogenic variant cannot be detected in the leukocyte DNA of his mother, the male sibs are still at increased risk (<5%) of being affected.

Offspring of a proband. Affected males transmit the BTK pathogenic variant to:

• All of their daughters, who will be carriers and are not likely to be affected;
• None of their sons.

Other family members

• A male proband's maternal aunts may be at risk of being heterozygotes (carriers) for the pathogenic variant and the aunts' offspring, depending on their sex, may be at risk of being heterozygotes (carriers) for the pathogenic variant or of being affected.
• Linkage analysis has shown that the maternal grandfather is the source of a de novo pathogenic variant in the majority of males who have no family history of XLA and that the maternal grandmothers are carriers less than 20% of the time [Conley et al 1998]. Therefore, the risk that the maternal aunt of a boy with no family history of XLA is a carrier is less than 10%.

Heterozygote (Carrier) Detection

Molecular genetic testing of at-risk female relatives to determine their genetic status is most informative if the BTK pathogenic variant has been identified in the proband.

Note: (1) Females who are heterozygous (carriers) for this X-linked disorder are not likely to be affected. (2) Identification of female heterozygotes requires either (a) prior identification of the BTK pathogenic variant in the family or, (b) if an affected male is not available for testing, molecular genetic testing first by sequence analysis, and if no pathogenic variant is identified, by gene-targeted deletion/duplication analysis.

Related Genetic Counseling Issues

See Management, Evaluation of Relatives at Risk for information on evaluating at-risk relatives for the purpose of early diagnosis and treatment.

Family planning

• The optimal time for determination of genetic risk, clarification of carrier status, and discussion of the availability of prenatal/preimplantation genetic testing is before pregnancy.
• It is appropriate to offer genetic counseling (including discussion of potential risks to offspring and reproductive options) to young adults who are affected, are carriers, or are at risk of being carriers.

DNA banking. Because it is likely that testing methodology and our understanding of genes, pathogenic mechanisms, and diseases will improve in the future, consideration should be given to banking DNA from probands in whom a molecular diagnosis has not been confirmed (i.e., the causative pathogenic mechanism is unknown).

Prenatal Testing and Preimplantation Genetic Testing

Once the BTK pathogenic variant has been identified in an affected family member, prenatal testing for a pregnancy at increased risk and preimplantation genetic testing for X-linked agammaglobulinemia are possible.

Differences in perspective may exist among medical professionals and within families regarding the use of prenatal testing. While most centers would consider use of prenatal testing to be a personal decision, discussion of these issues may be helpful.

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Author History

Mary Ellen Conley, MD; St Jude Children’s Research Hospital (2001-2016)
Vanessa C Howard, RN, MSN; St Jude Children’s Research Hospital (2001-2016)
CI Edvard Smith, MD, PhD (2016-present)
Anna Berglöf, PhD (2016-present)

Revision History

• 4 August 2016 (bp) Comprehensive update posted live
• 17 November 2011 (me) Comprehensive update posted live
• 30 July 2009 (me) Comprehensive update posted live
• 21 December 2005 (me) Comprehensive update posted live
• 4 November 2004 (mec) Revision: test availability
• 3 October 2003 (me) Comprehensive update posted live
• 5 April 2001 (me) Review posted live
• December 2000 (mec) Original submission