Marianne Arnestad

Prevalence of Long-QT Syndrome Gene Variants in Sudden Infant Death Syndrome

Background— The hypothesis that some cases of sudden infant death syndrome (SIDS) could be caused by long-QT syndrome (LQTS) has been supported by molecular studies. However, there are inadequate data regarding the true prevalence of mutations in arrhythmia-susceptibility genes among SIDS cases. Given the importance and potential implications of these observations, we performed a study to more accurately quantify the contribution to SIDS of LQTS gene mutations and rare variants. Methods and Results— Molecular screening of 7 genes (KCNQ1, KCNH2, SCN5A, KCNE1, KCNE2, KCNJ2, CAV3) associated with LQTS was performed with denaturing high-performance liquid chromatography and nucleotide sequencing of genomic DNA from 201 cases diagnosed as SIDS according to the Nordic Criteria, and from 182 infant and adult controls. All SIDS and control cases originated from the same regions in Norway. Genetic analysis was blinded to diagnosis. Mutations and rare variants were found in 26 of 201 cases (12.9%). On the basis of their functional effect, however, we considered 8 mutations and 7 rare variants found in 19 of 201 cases as likely contributors to sudden death (9.5%; 95% CI, 5.8 to 14.4%). Conclusions— We demonstrated that 9.5% of cases diagnosed as SIDS carry functionally significant genetic variants in LQTS genes. The present study demonstrates that sudden arrhythmic death is an important contributor to SIDS. As these variants likely modify ventricular repolarization and QT interval duration, our results support the debated concept that an ECG would probably identify most infants at risk for sudden death due to LQTS either in infancy or later on in life.

Cardiac Sodium Channel Dysfunction in Sudden Infant Death Syndrome

Background— Mutations in genes responsible for the congenital long-QT syndrome, especially SCN5A, have been identified in some cases of sudden infant death syndrome. In a large-scale collaborative genetic screen, several SCN5A variants were identified in a Norwegian sudden infant death syndrome cohort (n=201). We present functional characterization of 7 missense variants (S216L, R680H, T1304M, F1486L, V1951L, F2004L, and P2006A) and 1 in-frame deletion allele (delAL586-587) identified by these efforts. Methods and Results— Whole-cell sodium currents were measured in tsA201 cells transiently transfected with recombinant wild-type or mutant SCN5A cDNA (hH1) coexpressed with the human &bgr;1 subunit. All variants exhibited defects in the kinetics and voltage dependence of inactivation. Five variants (S216L, T1304M, F1486L, F2004L, and P2006A) exhibited significantly increased persistent sodium currents (range, 0.5% to 1.7% of peak current) typical of SCN5A mutations associated with long-QT syndrome. These same 5 variants also displayed significant depolarizing shifts in voltage dependence of inactivation (range, 5 to 14 mV) and faster recovery from inactivation, but F1486L uniquely exhibits a depolarizing shift in the conductance-voltage relationship. Three alleles (delAL586-587, R680H, and V1951L) exhibited increased persistent current only under conditions of internal acidosis (R680H) or when expressed in the context of a common splice variant (delQ1077), indicating that they have a latent dysfunctional phenotype. Conclusions— Our present results greatly expand the spectrum of functionally characterized SCN5A variants associated with sudden infant death syndrome and provide further biophysical correlates of arrhythmia susceptibility in this syndrome.

Cardiac Potassium Channel Dysfunction in Sudden Infant Death Syndrome

Life-threatening arrhythmias have been suspected as one cause of the sudden infant death syndrome (SIDS), and this hypothesis is supported by the observation that mutations in arrhythmia susceptibility genes occur in 5-10% of cases. However, the functional consequences of cardiac potassium channel gene mutations associated with SIDS and how these alleles might mechanistically predispose to sudden death are unknown. To address these questions, we studied four missense KCNH2 (encoding HERG) variants, one compound KCNH2 genotype, and a missense KCNQ1 mutation all previously identified in Norwegian SIDS cases. Three of the six variants exhibited functional impairments while three were biophysically similar to wild-type channels (KCNH2 variants V279M, R885C, and S1040G). When co-expressed with WT-HERG, R273Q and K897T/R954C generated currents resembling the rapid component of the cardiac delayed rectifier current (I(Kr)) but with significantly diminished amplitude. Action potential modeling demonstrated that this level of functional impairment was sufficient to evoke increased action potential duration and pause-dependent early afterdepolarizations. By contrast, KCNQ1-I274V causes a gain-of-function in I(Ks) characterized by increased current density, faster activation, and slower deactivation leading to accumulation of instantaneous current upon repeated stimulation. Action potential simulations using a Markov model of heterozygous I274V-I(Ks) incorporated into the Luo-Rudy (LRd) ventricular cell model demonstrated marked rate-dependent shortening of action potential duration predicting a short QT phenotype. Our results indicate that certain potassium channel mutations associated with SIDS confer overt functional defects consistent with either LQTS or SQTS, and further emphasize the role of congenital arrhythmia susceptibility in this syndrome.

Can patients receiving opioid maintenance therapy safely drive? A systematic review of epidemiological and experimental studies on driving ability with a focus on concomitant methadone or buprenorphine administration.

Objective: To perform a systematic review of the present scientific literature on the treatment with methadone or buprenorphine related to (1) traffic accident risk in epidemiological studies and (2) their effects on cognitive and psychomotor functions of relevance to driving in experimental studies. Methods: Searches for corresponding literature were conducted in MEDLINE, EMBASE, and PsycINFO throughout March and June of 2010. The search strategy consisted of words colligated to accident risk and culpability, in addition to cognitive and psychomotor functions of relevance to driving, all in relation to methadone or buprenorphine administration. In total, 59 studies were included. Results: Early epidemiological studies found no substantial difference in motor vehicle accident risk between methadone maintenance therapy patients (MMPs) and control groups. However, more recent studies have found an increased risk of traffic accident involvement for both MMPs and buprenorphine maintenance therapy patients (BMPs). In experimental studies, impairments of cognitive and psychomotor functions have been observed among both MMPs and BMPs when compared to control groups. When comparing MMPs with BMPs, the latter appeared to be less impaired than MMPs, but this difference may be unrelated to the maintenance therapy. Further impairments have been observed among MMPs after single doses, after an additional versus regular daily dosing, in multiple versus single dosing, and after long-term treatment compared to baseline levels. All studies showed impairments among opioid-naïve subjects after the administration of a comparatively low and single dose of either methadone or buprenorphine. Conclusions: Both methadone and buprenorphine were confirmed as having impairing potentials in opioid-naïve subjects. At least some opioid maintenance therapy patients are observed having only slight impairments of relevance to driving. Knowing this when approaching the question of ability to drive, an individual evaluation of the driving performance, pertaining to the opioid maintained patient, may be the most useful and conclusive procedure. Supplemental materials are available for this article. Go to the publishers online edition of Traffic Injury Prevention to view the supplemental file.

Morphine to codeine concentration ratio in blood and urine as a marker of illicit heroin use in forensic autopsy samples.

A morphine to codeine ratio greater than unity (M/C>1) has been suggested as an indicator of heroin use in living individuals. The aim of this study was to examine the morphine to codeine ratio in a large population (N=2438) of forensically examined autopsy cases positive for 6-monoacetylmorphine (6-MAM) and/or morphine in blood and/or urine. Blood and urine concentrations of 6-MAM, morphine and codeine were examined using GC-MS and LC-MS/MS methods. In 6-MAM positive samples, the M/C ratio was greater than unity in 98% (N=917) of the blood samples and 96% (N=665) of the urine samples. Stratification of 6-MAM negative cases by M/C above or below unity revealed similarities in morphine and codeine concentrations in cases where M/C>1 and 6-MAM positive cases. Median blood and urine morphine concentrations were 8-10 times greater than codeine for both groups. Similarly to 6-MAM positive cases, 25-44 year-old men prevailed in the M/C>1 group. In comparison to cases where M/C ≤ 1, the M/C ratio was a hundred times higher in both 6-MAM positive and M/C>1 cases. The range of morphine concentration between the lowest and the highest quintile of codeine in M/C>1 cases was similar to that in 6-MAM positive cases. This range was much higher than for M/C ≤ 1 cases. Moreover, linear regression analyses, adjusted for age and gender, revealed a strong positive association between morphine and codeine in 6-MAM positive and M/C>1 cases. The M/C ratio appeared to be a good marker of heroin use in post-mortem cases. Both blood and urine M/C>1 can be used to separate heroin users from other cases positive for morphine and codeine.

Comparative epidemiology of sudden infant death syndrome and sudden intrauterine unexplained death

Background: Unexplained antepartum stillbirth and sudden infant death syndrome (SIDS) are major contributors to perinatal and infant mortality in the western world. A relation between them has been suggested. As an equivalent of SIDS, only cases validated by post mortem examination are diagnosed as sudden intrauterine unexplained death (SIUD). Objective: To test the hypothesis that SIDS and SIUD have common risk factors. Methods: Registration comprised all stillbirths in Oslo and all infant deaths in Oslo and the neighbouring county, Akershus, Norway during 1986–1995. Seventy six cases of SIUD and 78 of SIDS were found, along with 582 random controls surviving infancy, all singletons. Odds ratios were obtained by multiple logistic regression analysis. Results: Whereas SIUD was associated with high maternal age, overweight/obesity, smoking, and low education, SIDS was associated with low maternal age, smoking, male sex, multiparity, proteinuria during pregnancy, and fundal height exceeding +2 SD. Thus the effects of maternal age were opposite in SIUD and SIDS (adjusted odds ratio 1.39 (95% confidence interval 1.17 to 1.66) per year, p < 0.0005). Heavy smoking, male sex, and a multiparous mother was less likely in SIUD than in SIDS (0.22 (0.06 to 0.83), 0.22 (0.07 to 0.78), and 0.03 (<0.01 to 0.17) respectively). Overweight/obesity and low fundal height were more common in SIUD than in SIDS (7.45 (1.49 to 37.3) and 13.8 (1.56 to 122) respectively). Conclusions: The differences in risk factors do not support the hypothesis that SIDS and SIUD have similar determinants in maternal or fetal characteristics detectable by basic antenatal care.

A mitochondrial DNA polymorphism associated with cardiac arrhythmia investigated in sudden infant death syndrome

Aim: Long QT syndrome (LQTS) has been shown to be the cause of death in some cases originally diagnosed as sudden infant death syndrome (SIDS). Such cardiac arrhythmias have also been noted in families with mitochondrial disease, and studies indicate that mitochondrial disease could be involved in SIDS. This makes the mtDNA polymorphism T3394C interesting, as a previous study has shown it to be associated with electrocardiographic (ECG) changes after exercise in a family with LQTS, where some members harboured a KCNH2 mutation.

The G protein β3 subunit 825C allele is associated with sudden infant death due to infection

Aim: To investigate the Gβ3 subunit C825T polymorphism with regard to sudden unexpected infant death. The reported association between the Gβ3s protein and increased immune cell function in humans makes this polymorphism highly interesting both with regard to sudden infant death syndrome (SIDS) and deleterious infectious disease. Methods: The cases investigated in the present study consist of 250 SIDS cases, 38 cases of sudden unexpected infant death due to infection and 99 living infant controls. Typing of the C825T polymorphism was performed by real‐time PCR with allele‐specific probes and melting curve analyses. Results: The cases of infectious death have a higher percentage of both the C allele (p=0.037 compared to the SIDS cases, p=0.022 compared to the controls) and the CC genotype (p=0.05 compared to the SIDS cases, p=0.016 compared to the controls). There were no differences between SIDS cases and controls.

Are substitutions in the first hypervariable region of the mitochondrial DNA displacement-loop in sudden infant death syndrome due to maternal inheritance?

Aim: To investigate whether all substitutions in the first hypervariable region (HVR1) in sudden infant death syndrome (SIDS) can be recovered along the maternal line of the family (inherited), or whether SIDS victims have new substitutions compared to maternal relatives (somatic mutations) that may be related to environmental factors. Methods: Seventy‐one SIDS/mother pairs, including 11 families with SIDS, mother and mothers relatives and/or SIDS siblings, were studied. The HVR1 sequence was recorded in the base‐pair range 16056‐16400. The recorded HVR1 sequence was compared with the Cambridge sequence, and differences were recorded as substitutions. The substitution pattern in the SIDS victims was compared with the pattern found in family members along the maternal line. Results: All the substitutions found in SIDS victims could be traced in the maternal line of the family; in 5 cases this was observed through three generations, and in 3 cases through four generations. Discussion: In patients with known mitochondrial (mt) DNA disease, a large number of sequence variants have been found in the D‐loop region. Substitutions in the D‐loop may be part of a haplotype with mutations elsewhere in the mtDNA.

Mitochondrial tRNA genes and flanking regions in sudden infant death syndrome

Aim: Mitochondrial DNA (mtDNA) mutations have been proposed as a genetic risk factor for sudden infant death syndrome (SIDS). The aim of this study was to further investigate this issue, by sequencing the mitochondrial tRNA genes with flanking regions in SIDS cases and controls.