Second messenger role for Mg2+ revealed by human T-cell immunodeficiency.

The magnesium ion, Mg(2+), is essential for all life as a cofactor for ATP, polyphosphates such as DNA and RNA, and metabolic enzymes, but whether it plays a part in intracellular signalling (as Ca(2+) does) is unknown. Here we identify mutations in the magnesium transporter gene, MAGT1, in a novel X-linked human immunodeficiency characterized by CD4 lymphopenia, severe chronic viral infections, and defective T-lymphocyte activation. We demonstrate that a rapid transient Mg(2+) influx is induced by antigen receptor stimulation in normal T cells and by growth factor stimulation in non-lymphoid cells. MAGT1 deficiency abrogates the Mg(2+) influx, leading to impaired responses to antigen receptor engagement, including defective activation of phospholipase Cγ1 and a markedly impaired Ca(2+) influx in T cells but not B cells. These observations reveal a role for Mg(2+) as an intracellular second messenger coupling cell-surface receptor activation to intracellular effectors and identify MAGT1 as a possible target for novel therapeutics.

Combined immunodeficiency associated with DOCK8 mutations.

BACKGROUND: Recurrent sinopulmonary and cutaneous viral infections with elevated serum levels of IgE are features of some variants of combined immunodeficiency. The genetic causes of these variants are unknown. METHODS: We collected longitudinal clinical data on 11 patients from eight families who had recurrent sinopulmonary and cutaneous viral infections. We performed comparative genomic hybridization arrays and targeted gene sequencing. Variants with predicted loss-of-expression mutations were confirmed by means of a quantitative reverse-transcriptase-polymerase-chain-reaction assay and immunoblotting. We evaluated the number and function of lymphocytes with the use of in vitro assays and flow cytometry. RESULTS: Patients had recurrent otitis media, sinusitis, and pneumonias; recurrent Staphylococcus aureus skin infections with otitis externa; recurrent, severe herpes simplex virus or herpes zoster infections; extensive and persistent infections with molluscum contagiosum; and human papillomavirus infections. Most patients had severe atopy with anaphylaxis; several had squamous-cell carcinomas, and one had T-cell lymphoma-leukemia. Elevated serum IgE levels, hypereosinophilia, low numbers of T cells and B cells, low serum IgM levels, and variable IgG antibody responses were common. Expansion in vitro of activated CD8 T cells was impaired. Novel homozygous or compound heterozygous deletions and point mutations in the gene encoding the dedicator of cytokinesis 8 protein (DOCK8) led to the absence of DOCK8 protein in lymphocytes. CONCLUSIONS: Autosomal recessive DOCK8 deficiency is associated with a novel variant of combined immunodeficiency.

Hemorrhagic Stroke in an Adolescent Female with HIV-Associated Thrombotic Thrombocytopenic Purpura.

HIV-1 infection can trigger acute episodes of Idiopathic Thrombocytoponic Purpura (ITP), and Thrombotic Thrombocytopenic Purpura (TTP), particularly in populations with advanced disease and poor adherence to antiretroviral therapy (ART). These diseases should be distinguished because they respond to different treatments. Previous studies done in adults with HIV-TTP have recommended the prompt initiation or re-initiation of ART in parallel with plasma exchange therapy to improve the clinical outcome of these patients. Here, we describe a case of HIV-TTP resulting in an acute hemorrhagic stroke in a 16 year old female with perinatally acquired HIV infection and non-adherence to ART, who presented with severe thrombocytopenia, microangiopathic hemolytic anemia, and a past medical history of HIV-ITP. Both differential diagnosis and treatments for HIV-ITP and HIV-TTP were considered simultaneously. A decrease in plasma ADAMTS13 activity (<5%) without detectable inhibitory antibodies confirmed the diagnosis of HIV-TTP. Re-initiation of ART and plasma exchange resulted in a marked decrease in the HIV-RNA viral load, recovery of the platelet count, and complete recovery was achieved with sustained virologic suppression.

Genetic, clinical, and laboratory markers for DOCK8 immunodeficiency syndrome.

DOCK8 immunodeficiency syndrome (DIDS) is a combined immunodeficiency characterized by recurrent viral infections, severe atopy, and early onset malignancy. Genetic studies revealed large, unique deletions in patients from different families and ethnic backgrounds. Clinical markers of DIDS include atopic dermatitis, allergies, cutaneous viral infections, recurrent respiratory tract infections, and malignancy. Immune assessments showed T cell lymphopenia, hyper-IgE, hypo-IgM, and eosinophilia. The impaired lymphocyte functions in DIDS patients appear central for disease pathogenesis.