Sophisticated genetic tools have made possible the identification of the genes responsible for most well-described immunodeficiencies in the past 15 years. Mutations in Btk, components of the pre-B cell and B cell receptor (lambda5, Igalpha, Igbeta), or the scaffold protein BLNK account for approximately 90% of patients with defects in early B cell development. Hyper-IgM syndromes result from mutations in CD40 ligand, CD40, AID, or UNG in 70-80% of affected patients. Rare defects in ICOS or CD19 can result in a clinical picture that is consistent with common variable immunodeficiency, and as many as 10% of patients with this disorder have heterozygous amino acid substitutions in TACI. For all these disorders, there is considerable clinical heterogeneity in patients with the same mutation. Identifying the genetic and environmental factors that influence the clinical phenotype may enhance patient care and our understanding of normal B cell development.

Approximately 85% of patients with defects in early B-cell development have X-linked agammaglobulinemia (XLA), a disorder caused by mutations in the cytoplasmic Bruton's tyrosine kinase (Btk). Although Btk is activated by cross-linking of a variety of cell-surface receptors, the most critical signal transduction pathway is the one initiated by the pre-B cell and B-cell antigen receptor complex. Mutations in Btk are highly diverse, and no single mutation accounts for more than 3% of patients. Although there is no strong genotype/phenotype correlation in XLA, the specific mutation in Btk is one of the factors that influences the severity of disease. Mutations in the components of the pre-B cell and B-cell antigen receptor complex account for an additional 5-7% of patients with defects in early B-cell development. Patients with defects in these proteins are clinically indistinguishable from those with XLA. However, they tend to be younger at the time of diagnosis, and whereas most patients with XLA have a small number of B cells in the peripheral circulation, these cells are not found in patients with defects in micro heavy chain or Igalpha. Polymorphic variants in the components of the pre-B cell and B-cell receptor complex, particularly micro heavy chain and lambda5, may contribute to the severity of XLA.

Fatigue is a common symptom found in the adult oncology literature. However, little is known about its occurrence, causes, conceptual and operational definitions, and effective interventions in children and adolescents with cancer.The purpose of this study was to define and describe fatigue experienced by children and adolescents receiving treatment for cancer. A focus group approach was used to reveal the contextual understanding of fatigue through discussions. Eleven focus groups were convened during a 2-month period at two major children's cancer centers. Twenty-nine children participated in the focus groups: 14 were 7 to 12 years of age and 15 were 13 to 16 years of age. Focus groups were held separately for each age group, lasted from 30 to 45 minutes, and were audiotaped. The audiotapes were transcribed verbatim, and Ethnograph software was used to number the data to sort and code the information. Researchers at both study sites coded the data independently within the context of the unit of analyses, which, in this study, were the study questions. Codes and descriptions were developed for the definitions of fatigue, causes of fatigue, and what helps. Eight codes emerged from the children groups and 12 from the adolescent groups to define fatigue. Six codes were developed from the children groups and 12 from the adolescent groups to describe causes of fatigue. Three codes from the children groups and eight from the adolescent groups described what helps. This study is the first to evaluate fatigue as a symptom in children and adolescents with cancer. Findings from this study will provide the foundation for developing a conceptual model for cancer-related fatigue in children and adolescents.

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