The gene encoding the gamma chain of the lymphocyte interleukin-2 receptor has been cloned and shown to be required to associate with the beta chain in order for IL-2 internalization and cell activation to occur (1). We considered this gene, IL2RG, a candidate for the X-linked form of severe combined immunodeficiency at the SCIDX1 locus, in which affected males have impaired lymphocyte development. Using fluorescence in situ hybridization and PCR amplification of somatic cell hybrid DNAs, we mapped IL2RG to human Xq13.1, a location within the SCIDX1 critical region established by linkage analysis. The 4.2 kb IL2RG gene was sequenced, and its genomic organization was elucidated. Seven of 19 transformed B-lymphocyte cell lines with independent SCIDX1 mutations had absent or minimal IL2RG mRNA. Unique point mutations were documented to be specifically associated with the disease and the carrier state in four unrelated affected males and their family members: one in a boy with no detectable IL2RG mRNA, in which the mutation ablated a splice donor site; one causing premature chain termination; and two causing distinct amino acid changes. The demonstration of impaired IL2RG mRNA expression in males with X-linked SCID and of unique point mutations in SCIDX1 pedigrees constitutes powerful evidence that the SCIDX1 gene is IL2RG. Noguchi et al. (2) have independently published IL2RG mapping to Xq13 and discovery of mutations in three affected males. The specific pathogenesis of IL2RG mutations and approaches to gene therapy can now be addressed in the X-linked form of SCID.

Mixed infections with seasonal influenza A virus strains are a common occurrence and an important source of genetic diversity. Prolonged viral shedding, as observed in immunocompromised individuals, can lead to mutational accumulation over extended periods. Recently, drug resistance was reported in immunosuppressed patients infected with the 2009 pandemic influenza A (H1N1) virus within a few days after oseltamivir treatment was initiated. To better understand the evolution and emergence of drug resistance in these circumstances, we used a deep sequencing approach to survey the viral population from an immunosuppressed patient infected with H1N1/2009 influenza and treated with neuraminidase inhibitors. This patient harbored 3 genetic variants from 2 phylogenetically distinct viral clades of pandemic H1N1/2009, strongly suggestive of mixed infection. Strikingly, one of these variants also developed drug resistance de novo in response to oseltamivir treatment. Immunocompromised individuals may, therefore, constitute an important source of genetic and phenotypic diversity, both through mixed infection and de novo mutation.

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Primary cutaneous marginal zone lymphoma (PCMZL) has rarely been reported in teenagers and is occasionally associated with Borrelia burgdorferi infection. Juxta-articular fibrotic nodules represent a unique, localized fibrosing response to spirochete infections, namely Borreliosis. Herein, we report a 15-year-old healthy boy who presented with a 4-year history of progressive acquisition of asymptomatic, erythematous nodules, ≤ 3 cm, beginning with his right forearm (3), then right arm (1) and lastly his right inner thigh (1). Biopsy showed PCMZL in three of five samples, and inflamed, fibrotic nodules, near the elbow in two. The bottom heavy lymphomatous nodules consisted of mostly small CD20+ CD43+ lymphocytes, some with plasmacytoid features. Mature plasma cells were lambda light chain restricted by in situ hybridization. The juxta-articular fibrotic nodules were located in the deep dermis and subcutis, had peripheral plasma cell-rich infiltrates, and showed nodular sclerosis (morphea profunda-like) in one, and lamellar and angiocentric sclerosis in the other reminiscent of quiescent lesions of chronic localized fibrosing leukocytoclastic vasculitis. Immunohistochemistry for B. burgdorferi revealed rare positive organisms; however, polymerase chain reaction (PCR) and serology were negative for B. burgdorferi as were serologic and/or PCR assays for Bartonella henselae, Ba. quintana, Ehrlichia chaffeensis, Treponema pallidum, Helicobacter pylori and Babesia microti. No evidence of extracutaneous disease was found by the review of systems and imaging studies. A 4-week trial of doxycycline therapy failed, whereas intralesional (IL) corticosteroid therapy induced rapid regression of his nodules. After two local recurrences, also treated with IL corticosteroids, he is well, without cutaneous disease, 20 months later. A literature review of 19 pediatric cases PCMZL reveals a similar natural history as adult PCMZL. Despite negative serology and PCR for B. burgdorferi, the occurrence of ipsilateral juxta-articular fibrotic nodules, positive B. burgdorferi immunohistochemistry and rapid response to IL corticosteroids implicate the presence of a replicative or non-replicative infectious (spirochetal) antigen in the initiation and promotion of this teenager's PCMZL.

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Neurocutaneous melanocytosis (NCM) is a rare disease characterized by excessive proliferation of melanocytes in the leptomeninges and brain parenchyma, primarily occurring in children with large or giant congenital melanocytic nevi (LCMN) or multiple congenital melanocytic nevi. [1][2][3] LCMN is diagnosed in an estimated 1/20 000-1/50 000 births with NCM identified in up to 30% of these individuals. 1,3 On magnetic resonance imaging (MRI), NCM can be identified as multifocal T1 shortening involving the brain or spine or diffuse leptomeningeal thickening. 4,5 Clinical manifestations of NCM are variable, ranging from asymptomatic melanocytosis to multiple cranial neuropathies, seizures, and symptomatic hydrocephalus. [1][2][3][4][5] Large or giant congenital melanocytic nevi or multiple congenital melanocytic nevi and NCM are associated with risk of cutaneous and central nervous system (CNS) melanoma. 1,6,7 In patients with LCMN or multiple congenital melanocytic nevi, an abnormal MRI represents the most significant predictor for development of melanoma. 7

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