KVLQT1 mutations in three families with familial or sporadic long QT syndrome

Congenital long QT syndrome (LQTS) is a heterogeneous group of heritable disorders characterized by prolongation of the QT interval on the electrocardiogram, ventricular arrhythmias and sudden death. At least four genes can, when mutated, produce this phenotype. Of these genes, the recently identified KVLQT1 potassium channel is thought to be the one most commonly responsible. In this study, we used single strand conformational polymorphism (SSCP) analysis to screen two large and nine small LQTS families for mutations of the KVLQT1 potassium channel gene. We identified a novel missense mutation in two unrelated families which substitutes a serine for a conserved glycine in the putative pore region of the KVLQT1 channel. In a third family, a new alanine to valine mutation at a CpG dinucleotide resulted in the spontaneous occurrence of the long QT syndrome in monozygotic twin offspring of unaffected parents. Mutations at this same nucleotide have been observed in eight of the 19 LQTS families determined to have KVLQT1 mutations, suggesting this is a mutational hot spot. Both of these mutations alter the amino acid sequence in, or adjacent to, the pore of the channel and many diminish the channel's ability to conduct a repolarizing potassium current. To date, all KVLQT1 mutations determined to cause the LQTS are missense mutations. These data confirm the role of KVLQT1 in the LQTS and suggest that mutant KVLQT1 proteins may exert a dominant negative effect on repolarizing potassium currents by forming multimers with normal potassium channel protein subunits, dramatically reducing the number of fully-functional KVLQT1 channels.

The E1 protein is mandatory for pore formation by Semliki Forest virus spikes

Insect cells (Aedes albopictus, clone C6/36) were infected with various variants of Semliki Forest virus including the wild type using the SFV replicon system. The variants included deletion mutants lacking one of the structural proteins and a mutant with a point mutation in p62 (SQL). The latter mutation results in a failure to process p62 to E2 and E3. After infection of the cells with different variant viruses and subsequent expression of viral proteins in the host cell plasma membrane low pH-induced pore formation was detected by measuring the efflux of a radiolabeled compound. The results of these experiments clearly showed that the E1 protein is mandatory for the acid-induced pore formation. A participation of the 6K or C-protein could be excluded. Furthermore, results obtained with the SQL mutant suggest that dissociation of the E1/E2 heterodimer and subsequent homooligomerization of E1 are required for pore formation.

Gender comparisons of cognitive performances among vascular dementia, Alzheimer disease, and older adults without dementia

BACKGROUND

We hypothesized that women with Alzheimer disease (AD) would perform worse on a test of semantic memory but not on tests of other cognitive domains. We did not expect that women without dementia would perform more poorly than men without dementia on the same task.

OBJECTIVE

To explore the specificity of a semantic memory deficit among women with AD by exploring gender differences among a group of subjects with vascular dementia (VD).

DESIGN

A case-control study in which differences between men and women were explored using regression models to control for the potentially confounding effects of age, education, duration of dementia, and severity of dementia.

SETTING

Alzheimer's Disease Research Center Consortium of Los Angeles and Orange Counties, California.

SUBJECTS

Volunteers, recruited from the community or clinic referrals, who met clinical criteria for AD (n = 159) or VD (n = 117) or met criteria for control status without dementia (n = 134).

MAIN OUTCOME MEASURES

Five neuropsychological measures, commonly used in the diagnosis and assessment of dementia.

RESULTS

Women with VD scored lower than men with VD on 3 tests. However, when controlling for potential confounds, the gender difference was maintained only for the semantic memory task. Women with AD showed a strong trend to perform worse than men with AD on the test of semantic memory only. No gender differences were found among subjects without dementia.

CONCLUSIONS

Findings support the existence of a semantic memory deficit for women with AD and suggest that a similar deficit may exist among women with VD.

Electrogram patterns associated with successful radiofrequency ablation of accessory pathways in children

Electrograms observed prior to successful and unsuccessful ablation trials in 33 patients (362 attempts) with manifest pathways and 18 patients (194 attempts) with concealed pathways were compared to identify the electrogram patterns that are associated with successful radiofrequency ablation of accessory atrioventricular connections in young patients (mean age 12.7 years; range 4-22 years). Success was defined as permanent or transient interruption of conduction in the accessory connection. Predictors of success in patients with manifest pathways were local ventricular preexcitation (p &equals 0.0001), left-sidedness (43 or 174) of the accessory connection compared (p &equals 0.04) to right-sidedness (27 of 172), a probable Kent bundle potential (29 of 84 versus 39 of 256; p &equals 0.0001), and short antegrade atrioventricular conduction intervals (53.1 +/- 31.9 ms versus 64.6 +/- 32.0 ms; p &equals 0.02). Predictors of success in patients with concealed pathways were short ventriculoatrial conduction times (103.3 +/- 35.8 ms versus 117.9 +/- 34.8 ms; p &equals 0.01), and left-sided (42 of 125) pathways (p &equals 0.03; versus right-sided, 11 of 60). The presence of a Kent bundle potential was not significant. We conclude that specific electrogram patterns can predict successful ablation of either manifest or concealed accessory pathways. Use of these criteria may reduce the delivery of unnecessary energy to young myocardium.

Vision in dementia: contrast effects

Contrast sensitivity has been shown to be affected in Alzheimer's disease (Ad). We investigated low contrast acuity and contrast sensitivity using clinical test charts in this patient population. Additionally, we tested patients with vascular dementia (vd) and mixed dementia (md), (Alzheimer' with vascular dementia). Contrast sensitivity was assessed using the Vistech VCTS 6500 test chart. Low contrast acuity was measured using the Regan charts at four contrast levels (96%, 50%, 25% and 11%). The patient population consisted of 19 Ad patients, 9 vd patients and 10 md patients. Reduction in acuity was found with contrast level in all cases. Regression lines were fit to the data and statistical analysis was performed. We did not find a statistically significant difference between the Ad and vd or md groups. We did, however, find a difference between the vd and md groups. We did find reduction in contrast sensitivity at all spatial frequencies when compared to the elderly normal. Correspondingly, we found a significant difference in acuity when compared with normal data at the four contrast levels tested. Acuity is reduced with contrast in all patient groups. Our contrast sensitivity results are similar to those reported in the literature. This study points out the importance of using simple clinical test charts and further underscores the idea that there is a primary visual deficit in Ad.

The molecular genetics of the congenital long QT syndromes

During the past half decade, significant insight into the clinical electrocardiographic, and genetic features of the congenital long QT syndromes has emerged. Based on this foundation, recent linkage analysis studies have demonstrated the genetic heterogeneity of the Romano-Ward long QT syndrome and led to the discovery of two of the four (or more) responsible genes. Further functional characterization of these two genes, the HERG potassium channel and the SCN5A voltage-gated cardiac sodium channel, as well as the identification and characterization of the other long QT syndrome genes, may allow improved diagnosis and therapy for these disorders. Furthermore, the increased understanding of myocardial repolarization that is gained from characterization of these genes may lead to improved treatment for other ventricular arrhythmias, including those related to potassium-channel blockade, central nervous system insult, and, possibly, myocardial infarction.

Peritoneal migration of an abdominally implanted epicardial pacemaker: a cause of intestinal obstruction

We report the case of a 10-year-old child with an abdominally implanted epicardial pacemaker that eroded through the peritoneum and migrated to an intraperitoneal location, resulting in partial and then complete intestinal obstruction. This potentially life-threatening complication should be considered when a patient with an abdominally implanted pacemaker presents with abdominal pain.

The use of radiofrequency energy in pediatric cardiology

The use of radiofrequency energy for the treatment of supraventricular tachycardia in pediatric patients has gained widespread acceptance, especially for tachyarrhythmias associated with palpitations, dizziness, presyncope or syncope, cardiomyopathy, and cardiac arrest. Ablation of the substrate supporting atrioventricular reentry, atrioventricular node reentry, and automatic atrial tachycardia yields a 90%-98% success rate with low incidence (< 1%) of complications and adverse side-effects. Ablation of intra-atrial reentry, including atrial flutter and fibrillation, appears to be promising and would be a significant advance in the management of patients following extensive atrial surgery for congenital heart disease. Radiofrequency energy is also used to treat various forms of idiopathic ventricular tachycardia. Finally, radiofrequency energy has been extended to control the ventricular rate associated with malignant atrial tachycardia by either modification or ablation of the atrioventricular node, and subsequent pacemaker implant. Long-term outcome of radiofrequency ablation is unknown, but the short-to-intermediate (1-5 yrs) outcome is excellent, with low recurrence rate of the tachycardia, no proarrhythmic effect, and excellent clinical state.

Randomized comparison of atenolol and fludrocortisone acetate in the treatment of pediatric neurally mediated syncope

Overall, these results indicate that oral treatment of neurally mediated syncope is safe and efficacious. Further randomized trials in children will be required to determine the significance of a placebo effect, as well as potential differences in results related to the mechanism of syncope.

Developmental regulation of expression and activity of multiple forms of the Drosophila RAC protein kinase

We have characterized the Drosophila homologue of the proto-oncogenic RAC protein kinase (DRAC-PK). The DRAC-PK gene gives rise to two transcripts with the same coding potential, generated by the use of two different polyadenylation signals. Each transcript encodes two polypeptides because of the presence of a weaker initiator ACG codon, upstream from the major AUG, such that the larger protein contains an N-terminal extension. Like the human isoforms, DRAC-PKs possess a novel signaling region, the pleckstrin homology domain. DRAC-PK proteins have a similar expression pattern, being regulated both maternally and zygotically, and are expressed throughout Drosophila development. Antisera specific for recombinant DRAC-PK and for its C terminus detected two polypeptides of 66 and 85 kDa in Drosophila extracts. The antirecombinant antisera also recognized a polypeptide of 120 kDa from Drosophila, which apparently shared an epitope related to DRAC-PK sequences. The role of p120 appears to be restricted compared with that of DRAC-PK, since it was not detected in larvae or adult flies. There was no spatial restriction of DRAC-PK expression during embryogenesis, suggesting that localized activation might be a regulatory mechanism for its function. DRAC-PK possesses an intrinsic kinase activity that is approximately 8-fold higher in adult flies than in 0-3-h embryos undergoing rapid mitotic cycles.

Catheter interruption of atrioventricular conduction using radiofrequency energy in a patient with transposition of the great arteries

Percutaneous catheter mapping and radiofrequency ablation of the AV node-His bundle system (with subsequent transvenous endocardial ventricular pacing) were performed on an 18-year-old woman with transposition of the great arteries and intact ventricular septum and chronic arrhythmias 15 years following a Mustard operation. Exclusion of the AV conduction tissue from the systemic venous circulation by the complex anatomy and the Mustard repair was circumvented by a retrograde approach across the aortic valve to the morphological right ventricle yielding access to the AV node-His bundle system.

Haemophilus influenzae type B invasive disease in urban and rural children: immunization patterns and prevalence of disease

To examine the impact of the introduction of Haemophilus influenzae type b (Hib) conjugate vaccine, we reviewed the incidence of Hib invasive disease in the state of Florida from 1984 to 1992. We analyzed the incidence of disease in two populations of children, one residing in an urban area and the other in a rural area. This study was designed to compare incidence rates prior to and following the introduction of Hib vaccine for children. Our data show a > 80% decrease in the incidence of Hib invasive disease in the state of Florida and a similar decrease in both the urban and rural populations examined. Analysis of the data revealed that the majority of children contracting Haemophilus influenzae type b invasive disease in both populations were either not immunized or were only partially immunized.

Decreased levels of C1q in cerebrospinal fluid of living Alzheimer patients correlate with disease state

Recent reports that complement proteins comprising the classical pathway are associated with senile plaques suggest that activation of the classical complement cascade in Alzheimer's disease tissue results in bystander cell lysis and may contribute to AD neuropathology. Analysis of cerebrospinal fluid may prove to be a useful means of detecting changes in immunological activity in the brain. We use an enzyme-linked immunosorbent assay to measure levels of C1q, a subunit of the classical complement cascade, in the CSF of patients clinically diagnosed with possible or probable AD. Significantly lower levels of C1q were detected in the CSF of the Alzheimer group as compared to control CSF [AD: mu = 268 ng/ml, SD = 84; non-AD: mu = 340 ng/ml, SD = 76; F(1, 44) = 5.84, p = 0.02]. Diminished performance on global measures of mental status such as the Mini-Mental State Exam (R = 0.45; p = 0.0072) and Blessed's Information, Memory, and Concentration test (R = 0.42; p = 0.0138) showed high correlations with decreased C1q levels. More specific measures of cognitive function, such as word recall (R = 0.42; p = 0.012), word recognition (R = 0.52; p = 0.0017) and delayed recall (R = 0.45; p = 0.0062) memory tasks also correlated strongly with decreased C1q levels.

Serum aldosterone concentrations and urine output in oliguric intensive care unit patients receiving low-dose dopamine

OBJECTIVE

To determine whether the diuretic and natriuretic effects of low-dose dopamine (2.5 micrograms/kg/min) are associated with changes in serum aldosterone concentration.

DESIGN

Prospective clinical study.

SETTING

Surgical intensive care unit (SICU) of a university hospital.

PARTICIPANTS

Oliguric (urine output < 0.5 mL/kg/h) SICU patients. All patients were resuscitated to pulmonary artery occlusion pressure > 10 mm Hg, mean arterial pressure > 65 mm Hg, and cardiac index > 2.5 L/min/m2. Patients with a serum creatinine concentration > 176.8 mumol/L (2.0 mg/dL), those who received diuretics within 12 hours prior to entry into the study, and renal transplant recipients were excluded.

MAIN OUTCOME MEASURES

Hourly urine output (mean +/- SD) was recorded 2 hours before and for 6 hours after the initiation of low-dose dopamine. Urine sodium and serum aldosterone concentrations were obtained prior to and 6 hours after the start of low-dose dopamine.

RESULTS

Fifteen patients were enrolled in the study. Urine output (mean +/- SD) increased from 0.31 +/- 0.11 mL/kg/h before to 0.80 +/- 0.34 mL/kg/h following low-dose dopamine (p < 0.01). Urine sodium concentrations increased from 46 +/- 32 mmol/L baseline to 72 +/- 53 mmol/L following low-dose dopamine (p < 0.05), and serum aldosterone concentrations decreased from 415.82 +/- 341.48 pmol/L prior to low-dose dopamine infusion to 256.04 +/- 204.17 pmol/L (p < 0.05). Cardiac output, pulmonary artery occlusion pressure, mean arterial pressure, and heart rate did not change.

CONCLUSIONS

Low-dose dopamine significantly increases urine output and urine sodium excretion in oliguric, critically ill, surgical patients, and is associated with a decrease in serum aldosterone concentration. The diuretic and natriuretic effects of low-dose dopamine may be, in part, related to a dopamine-mediated inhibition of aldosterone secretion.

Delayed response to radiofrequency ablation of accessory connections

This article summarizes delayed interruption in anomalous conduction through accessory connections following radiofrequency ablation attempts in three patients. The time course of the delayed interruption in accessory connection conduction suggests that such an effect is unlikely to occur after the first week following unsuccessful radiofrequency ablation.

HOM/Hox type homeoboxes in the chelicerate Limulus polyphemus

The polymerase chain reaction was used to survey HOM/Hox type homeobox genes in the North American horseshoe crab, Limulus polyphemus. The survey reveals 28 different homeobox fragments possessing 44-80% nucleotide sequence similarity with HOM-C sequences in Drosophila and Hox B sequences in mouse. Limulus has one to four representatives of HOM/Hox cognates when fragments are assigned according to amino acid identity. A parsimony analysis including the Limulus sequences and homologous mouse Hox B and Drosophila HOM-C sequences reveals several instances of monophyletic groupings of Limulus homeoboxes with a Drosophila or mouse gene as the sister branch. Under the current model of HOM/Hox cluster evolution, these results suggest that Limulus has as many as four HOM/Hox type clusters. This is the first evidence suggesting the presence of multiple clusters in a nonvertebrate taxon. Putative homologs of mouse Hoxb-3 in Limulus suggest that the gene was present in the common ancestor of arthropods and vertebrates and has been lost in Drosophila.