Targeted Gene Sanger Sequencing Should Remain the First-Tier Genetic Test for Children Suspected to Have the Five Common X-Linked Inborn Errors of Immunity.

To address inborn errors of immunity (IEI) which were underdiagnosed in resource-limited regions, our centre developed and offered free genetic testing for the most common IEI by Sanger sequencing (SS) since 2001. With the establishment of The Asian Primary Immunodeficiency (APID) Network in 2009, the awareness and definitive diagnosis of IEI were further improved with collaboration among centres caring for IEI patients from East and Southeast Asia. We also started to use whole exome sequencing (WES) for undiagnosed cases and further extended our collaboration with centres from South Asia and Africa. With the increased use of Next Generation Sequencing (NGS), we have shifted our diagnostic practice from SS to WES. However, SS was still one of the key diagnostic tools for IEI for the past two decades. Our centre has performed 2,024 IEI SS genetic tests, with in-house protocol designed specifically for 84 genes, in 1,376 patients with 744 identified to have disease-causing mutations (54.1%). The high diagnostic rate after just one round of targeted gene SS for each of the 5 common IEI (X-linked agammaglobulinemia (XLA) 77.4%, Wiskott-Aldrich syndrome (WAS) 69.2%, X-linked chronic granulomatous disease (XCGD) 59.5%, X-linked severe combined immunodeficiency (XSCID) 51.1%, and X-linked hyper-IgM syndrome (HIGM1) 58.1%) demonstrated targeted gene SS should remain the first-tier genetic test for the 5 common X-linked IEI.

Susceptibility to mycobacterial infections in children with X-linked chronic granulomatous disease: a review of 17 patients living in a region endemic for tuberculosis.

BACKGROUND: Chronic granulomatous disease (CGD) is a rare disorder of phagocytic oxidative bursts leading to recurrent pyogenic infections. Affected individuals are most prone to infections caused by staphylococci, Salmonella, Candida, and Aspergillus, but previously we observed a high incidence of Mycobacterium tuberculosis infection in Chinese children with CGD. OBJECTIVE: To determine the spectrum of infections in patients with X-linked CGD, with an emphasis on mycobacterial infections, and to review all CYBB gene mutations identified in our center. RESULTS: From 1988 to 2005, 17 Chinese male children were diagnosed to have X-linked CGD. Fifteen mutations were identified, including 3 splice site defects (IVS1-1G>C, 266G>A, IVS3-1G>A), 5 missense mutations (591T>C, 627T>A, 949T>A, 1039T>A, 1512G>C), 3 nonsense mutations (882C>T, 1451C>A, 1569G>T), 1 insertion (756_757insA), and 3 deletions (660_662delTTC, 727delT, 1341delT). Eight of these were novel mutations. Recurrent pneumonia, lymphadenitis, and bacterial skin abscess were the commonest types of infection. Seven patients had tuberculosis (TB). Seven patients had prolonged scarring or abscess formation at the Calmette-Guérin bacillus (BCG) injection site, and 1 had disseminated BCG infection. Three patients had pulmonary aspergillosis. Four patients underwent hemopoietic stem cell transplantation, but 2 died of complications. CONCLUSIONS: Patients with CGD are susceptible to TB and BCG complications. Our observation suggests that oxidative burst is probably important in host defense against mycobacterial infections. Because interferon-gamma is the key cytokine involved in mycobacterial immunity, there may be a stronger indication for its use in CGD patients living in areas endemic for TB.