Plasma-membrane calcium pumps and hereditary deafness.

In mammals, four different genes encode four PMCA (plasma-membrane Ca(2+)-ATPase) isoforms. PMCA1 and 4 are expressed ubiquitously, and PMCA2 and 3 are expressed predominantly in the central nervous system. More than 30 variants are generated by mechanisms of alternative splicing. The physiological meaning of the existence of so many isoforms is not clear, but evidently it must be related to the cell-specific demands of Ca(2+) homoeostasis. Recent studies suggest that the alternatively spliced regions in PMCA are responsible for specific targeting to plasma membrane domains, and proteins that bind specifically to the pumps could contribute to further regulation of Ca(2+) control. In addition, the combination of proteins obtained by alternative splicing occurring at two different sites could be responsible for different functional characteristics of the pumps.

A functional study of plasma-membrane calcium-pump isoform 2 mutants causing digenic deafness.

Ca2+ enters the stereocilia of hair cells through mechanoelectrical transduction channels opened by the deflection of the hair bundle and is exported back to endolymph by an unusual splicing isoform (w/a) of plasma-membrane calcium-pump isoform 2 (PMCA2). Ablation or missense mutations of the pump cause deafness, as described for the G283S mutation in the deafwaddler (dfw) mouse. A deafness-inducing missense mutation of PMCA2 (G293S) has been identified in a human family. The family also was screened for mutations in cadherin 23, which accentuated hearing loss in a previously described human family with a PMCA2 mutation. A T1999S substitution was detected in the cadherin 23 gene of the healthy father and affected son but not in that of the unaffected mother, who presented instead the PMCA2 mutation. The w/a isoform was overexpressed in CHO cells. At variance with the other PMCA2 isoforms, it became activated only marginally when exposed to a Ca2+ pulse. The G293S and G283S mutations delayed the dissipation of Ca2+ transients induced in CHO cells by InsP3. In organotypic cultures, Ca2+ imaging of vestibular hair cells showed that the dissipation of stereociliary Ca2+ transients induced by Ca2+ uncaging was compromised in the dfw and PMCA2 knockout mice, as was the sensitivity of the mechanoelectrical transduction channels to hair bundle displacement in cochlear hair cells.

Increased anticardiolipin antibody IgG titers do not predict recurrent stroke or TIA in children.

BACKGROUND: Increased anticardiolipin antibody (ACLA) immunoglobulin (Ig) G titers are commonly found in children with arterial ischemic stroke (AIS) or TIA (AIS/TIA). The associated risk of recurrent thromboembolism is unknown. OBJECTIVE: To determine the risk of recurrent thromboembolism associated with persistently increased ACLA titers of the IgG isotype in children with AIS/TIA. METHODS: The authors studied a cohort of children surviving first AIS/TIA tested by standardized ELISA for beta2-glycoprotein I-dependent ACLA of the IgG isotype. Children with ACLA titers >15 IgG phospholipid (GPL) units (per manufacturer's cutoff point) on more than two occasions > or =6 weeks apart were classified as ACLA-positive (ACLA+) and compared with ACLA-negative (ACLA-) children with respect to recurrent thromboembolic events (AIS/TIA, sinovenous thrombosis, and extracerebral thromboembolism). RESULTS: The authors recruited 34 ACLA+ children and 151 ACLA- children. Most ACLA+ children (30/34; 88%) had ACLA titers < or =40 GPL units. During the follow-up period (median duration, 2.8 years for ACLA+ children and 3.0 years for ACLA- children), AIS/TIA recurred in 26% of ACLA+ children and in 38% of ACLA- children; none developed sinovenous thrombosis or extracerebral thromboembolism. Based on survival analysis, this difference was nonsignificant (p = 0.54). Using binary partition evaluation, no titer criteria for ACLA positivity (range, 0 to 60 GPL units) predicted recurrent AIS/TIA. CONCLUSION: In children surviving arterial ischemic stroke/TIA, increased anticardiolipin antibody immunoglobulin G titers do not predict recurrent thromboembolism.

Presumed pre- or perinatal arterial ischemic stroke: risk factors and outcomes.

A subgroup of children with arterial ischemic stroke in the pre- or perinatal period present with delayed diagnosis. We identified 22 children who met the following criteria: (1) normal neonatal neurological history, (2) hemiparesis and/or seizures first recognized after two months of age, and (3) computed tomography or magnetic resonance imaging showing remote cerebral infarct. Laboratory evaluations included protein C, protein S, antithrombin, activated protein C resistance screen (APCR), Factor V Leiden (FVL), prothrombin gene defect, methylene tetrahydrofolate reductase variant (MTHFR), anticardiolipin antibody (ACLA), and lupus anticoagulant. Not all children received all tests. Age at last visit ranged from 8 months to 16.5 years (median 4 years). Twelve were boys. Fourteen had left hemisphere infarcts. Median age at presentation was 6 months. Eighteen had gestational complications. Fourteen children had at least transient coagulation abnormalities (ACLA = 11, ACLA + APCR = 1, APCR = 2 with FVL + MTHFR = 1); six of these children had family histories suggestive of thrombosis. Cardiac echocardiogram was unremarkable in the 15 tested. Outcomes included persistent hemiparesis in 22; speech, behavior, or learning problems in 12; and persistent seizures in five, with no evidence of further stroke in any patient. The persistence and importance of coagulation abnormalities in this group need further study.