Bruton tyrosine kinase gene mutations in Turkish patients with presumed X-linked agammaglobulinemia

Clinical and genetic profiles of patients with X-linked agammaglobulinemia from southeast Turkey: Novel mutations in BTK gene

BACKGROUND

X-linked agammaglobulinemia (XLA) is characterized by absent or severely reduced B cells, low or undetectable immunoglobulin levels, and clinically by extracellular bacterial infections which mainly compromise the respiratory tract. We aimed to analyze the clinical, immunological and genetic characteristics of 22 male children with XLA.

METHODS

Twenty-two children with XLA from 12 unrelated families were enrolled in this study. Clinical and demographic features of patients, serum immunoglobulin levels, percentage of B cells and BTK gene mutations were reviewed retrospectively.

RESULTS

We identified 12 different mutations in 22 patients from 12 unrelated families. The most frequent type of mutation was premature stop codon (33.3%). Ten mutations had been reported previously including three missense mutations (c.1774T>C, c.1684C>T, c.83G>T), three premature stop codons (c.1558C>T, c.1573C>T, c.753G>A), two splice-site (c.683-1G>A, c.1567-12_1567-9delTTTG) and two small nucleotide deletions (c.902-904_delAAG, c.179_181delAGA). Two novel mutations of the BTK gene were also presented and included one splice-site mutation (c.391+1G>C) and one premature stop codon mutation (c.1243_1243delG). Six out of 12 mutations of the BTK gene were located in the SH1 domain, two in the PH domain, two in the SH3 domain and two in the SH2 domain. Three patients had a history of severe infection before diagnosis. We did not identify any correlation between severity of clinical symptoms and the genotype.

CONCLUSIONS

Our results show that mutations in southeast Turkey could be different from those in the rest of the world and molecular genetic tests are an important tool for early confirmed diagnosis of XLA.

Uncommon Infections in Children Suggest Underlying Immunodeficiency: A Case of Infective Endocarditis in a 3-Year-Old Male

Infective endocarditis (IE) results from bacterial or fungal infection and is associated with significant morbidity and mortality. Several known risk factors exist for endocarditis, and 90% of pediatric cases have an underlying structural or congenital heart disease or prosthetic heart valve. Literature on IE in previously healthy children is relatively sparse, and the pathogenesis and underlying risk factors remain mostly unknown. Our patient was a 3-year-old male with a unique presentation of IE. His lack of structural and congenital risk factors for endocarditis prompted further workup, and labs were consistent with insufficient immunoglobulin, suggesting a primary immunodeficiency (PAD). PAD presents as heightened susceptibility to infections, commonly seen as recurrent pneumonia, meningitis, septic arthritis, and otitis media. Pediatric patients commonly have infections, yet as many as in 1 in 2000 patients have PAD. Our case emphasizes the potential need for further investigation into PAD in a young patient with no known risk factors who develops an uncommon infection such as IE.

Clinical and genetic features of the patients with X-Linked agammaglobulinemia from Turkey: Single-centre experience

X-linked agammaglobulinemia is a primary immunodeficiency disorder resulting from BTK gene mutations. There are many studies in the literature suggesting contradictory ideas about phenotype-genotype correlation. The aim of this study was to identify the mutations and clinical findings of patients with XLA in Turkey, to determine long-term complications related to the disease and to analyse the phenotype-genotype correlation. Thirty-two patients with XLA diagnosed between 1985 and 2016 in Pediatric Immunology Department of Hacettepe University Ihsan Dogramaci Children's Hospital were investigated. A clinical survey including clinical features of the patients was completed, and thirty-two patients from 26 different families were included in the study. Getting early diagnosis and regular assessment with imaging techniques seem to be the most important issues for improving the health status of the patients with XLA. Early molecular analysis gives chance for definitive diagnosis and genetic counselling, but not for predicting the clinical severity and prognosis.

X-Linked Agammagobulinemia in a Large Series of North African Patients: Frequency, Clinical Features and Novel BTK Mutations

PURPOSE

X-linked agammagobulinemia (XLA) is a primary immunodeficiency caused by Bruton's tyrosine kinase (BTK) gene defect. XLA patients have absent or reduced number of peripheral B cells and a profound deficiency in all immunoglobulin isotypes. This multicenter study reports the clinical, immunological and molecular features of Bruton's disease in 40 North African male patients.

METHODS

Fifty male out of 63 (male and female) patients diagnosed with serum agammaglobulinemia and non detectable to less than 2% peripheral B cells were enrolled. The search for BTK gene mutations was performed for all of them by genomic DNA amplification and Sanger sequencing.

RESULTS

We identified 33 different mutations in the BTK gene in 40 patients including 12 missense mutations, 6 nonsense mutations, 6 splice-site mutations, 5 frameshift, 2 large deletions, one complex mutation and one in-frame deletion. Seventeen of these mutations are novel. This large series shows a lower frequency of XLA among male patients from North Africa with agammaglobulinemia and absent to low B cells compared with other international studies (63.5% vs. 85%). No strong evidence for genotype-phenotype correlation was observed.

CONCLUSIONS

This study adds to other reports from highly consanguineous North African populations, showing lower frequency of X-linked forms as compared to AR forms of the same primary immunodeficiency. Furthermore, a large number of novel BTK mutations were identified and could further help identify carriers for genetic counseling.

Clinical and mutational features of Vietnamese children with X-linked agammaglobulinemia

BACKGROUND

X-linked agammaglobulinemia (XLA) is a primary immune deficiency characterized by recurrent bacterial infections and profoundly depressed serum immunoglobulin levels and circulating mature B cells. It is caused by mutations of the Bruton tyrosine kinase (BTK) gene and is the most common form of inherited antibody deficiency. To our knowledge, this is the first report of XLA from Vietnam.

METHODS

We investigated the BTK gene mutations and clinical features of four unrelated Vietnamese children.

RESULTS

The mean ages at onset and at diagnosis were 2.5 and 8 years, respectively. All patients had a medical history of otitis media, pneumonia, and septicemia at the time of diagnosis. Other infections reported included sinusitis, bronchiectasis, arthritis, skin infections, meningitis, and recurrent diarrhea. We identified one previously reported mutation (c.441G >A) and three novel mutations: two frameshifts (c.1770delG and c.1742 delG), and one nonsense (c.1249A >T).

CONCLUSIONS

The delayed diagnosis may be attributable to insufficient awareness of this rare disease on the background of frequent infections even in the immunocompetent pediatric population in Vietnam. Our results further support the importance of molecular genetic testing in diagnosis of XLA.

Clinical, immunological and molecular characteristics of 37 Iranian patients with X-linked agammaglobulinemia

BACKGROUND

X-linked agammaglobulinemia (XLA) is a hereditary immunodeficiency characterized by an early onset of recurrent bacterial infections, a profound deficiency of all immunoglobulin isotypes and a markedly reduced number of peripheral B lymphocytes. Eighty-five percent of the patients with this phenotype have mutations in Bruton's tyrosine kinase (BTK) gene.

METHODS

To provide an informative outlook of clinical and immunological manifestations of XLA in Iran, 37 Iranian male patients with an age range of 1-34 years, followed over a period of 25 years, were studied. Twenty-four of the 37 patients were screened for BTK gene mutation using PCR-SSCP followed by direct sequencing. BTK protein expression assay was done by flow cytometry in 9 families.

RESULTS

All patients first presented with infectious diseases, the most common of which were respiratory tract infections. Eighteen different mutations were identified, 13 of which were novel: IVS1+5G>C, 1896G>A, 349delA, 1618C>T, 1783T>C, 2084A>G, 1346delT, 1351delGAG, 587A>G, IVS14-1G>A, IVS3+2T>C, 1482G>A, 1975C>A.

CONCLUSION

The fact that we found a great number of novel mutations in a relatively limited number of patients underlines the heterogeneity of BTK mutations in the Iranian population. The large number of new mutations indicates that extended studies in this region would be rewarding.