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predominance of g.70A>G mutation in Finnish patients can result in milder presentations. Consistent with previous reports, measured laboratory values correlated poorly with any assessed symptoms and despite clearly abnormal laboratory indices, few patients developed serious complications. Worldwide, of the 30 subjects with CHH and hematopoietic stem cell transplantation (HSCT) whose genotype has been reported, only 6 patients were homozygous for g.70A>G mutation. Only 1 Finnish child with CHH, homozygote for g.70A>G mutation, has required HSCT for severe hypoplastic anemia, not for immunodeficiency. Thus, selection of patients who would benefit from HSCT based on routinely available laboratory parameters is highly cumbersome in a cohort carrying predominantly RMRP g.70A>G mutations. The major limitation of this study is the retrospective nature of clinical data. Inclusion of only living patients left out those with CHH who had died of cancer or severe infections. Another limitation is the use of a single laboratory measurement per patient. Results of immunologic tests fluctuate over time and predicting any clinical course on the basis of cross-sectional laboratory values remains challenging. The observed high number of asymptomatic patients and individuals with clinical signs of humoral immunodeficiency only should be interpreted with caution because clinical features may occur and cumulate with time. Follow-up studies should assess the applicability of clinical and immunological phenotype correlations, including the potential to predict a more severe course (CID) in patients with lower CD3, CD8, and RTE counts. In summary, we demonstrated that approximately one-fourth of the surviving Finnish patients with CHH included in this study manifested clinical signs of CID, while another onefourth showed no signs of immunodeficiency despite laboratory immunologic abnormalities. This is the first report describing high prevalence of SAD and a specific pattern of abnormalities in Band T-cell compartments in patients with CHH. Svetlana Kostjukovits, MD Paula Klemetti, MD, PhD Helena Valta, MD, PhD Timi Martelius, MD, PhD Luigi D. Notarangelo, MD Mikko Sepp€ anen, MD, PhD Mervi Taskinen, MD, PhD Outi M€ akitie, MD, PhD From Children’s Hospital, University of Helsinki and Helsinki University Hospital, Helsinki, Finland; Folkh€alsan Research Center, Helsinki, Finland; the Department of Pediatrics, Malmi District Hospital, Pietarsaari, Finland; the Adult Immunodeficiency Unit, Inflammation Center, University of Helsinki and Helsinki University Hospital, Helsinki, Finland; the Laboratory of Host Defenses, Division of Intramural Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Md; and the Center for Molecular Medicine, Karolinska Institutet and Clinical Genetics, Karolinska University Hospital, Stockholm, Sweden. E-mail: [email protected]. The study was funded by the Sigrid Jus elius Foundation (O.M.), the Academy of Finland (O.M.), the Folkh€alsan Research Foundation (O.M.), the Helsinki University Hospital Research Funds (O.M. and M.T.), the Swedish Childhood Cancer Foundation (O.M.), the Foundation for Pediatric Research (O.M. and M.T.), the Finnish Medical Foundation (S.K.), and the Doctoral School in Health Sciences at the University of Helsinki (S.K.). The research was supported in part by the Intramural Research program of the National Institutes of Health, National Institute of Allergy and Infectious Diseases. Disclosure of potential conflict of interest: P. Klemetti has received a grant from the Foundation for Pediatric Research for this work. T. Martelius has received a grant from Sanguin; lecture fees fromMSD and CSL Behring; and travel grants from Octapharma, CSL Behring, Sanguin, Gilead, and MSD. L. D. Notarangelo has received board membership from the Journal of Clinical Immunology,Clinical Immunology, and Frontiers in Immunology; is employed by the National Institutes of Health and received royalties from UpToDate. M. Sepp€anen has received financial support for travel from CSL Behring and Octapharma for this work. M. Taskinen has received a grant from Helsinki University Hospital Research fund for this work. O. M€akitie’s institution has received grants from the Sigrid Jus elius Foundation, the Academy of Finland, the Folkh€alsan Research Foundation, Helsinki University Hospital Research Funds, the Swedish Childhood Cancer Foundation, and the Foundation for Pediatric Research for this work. The rest of the authors state that they have no relevant conflict of interest.