Toxic effects of mineral oil saturated hydrocarbons (MOSH) and relation to accumulation in rat liver.

Humans are daily exposed to mineral oil saturated hydrocarbons (MOSH) from the diet. We exposed female Fischer 344 rats to a broad mixture and sub-fractions of MOSH. Chemical characterization of the MOSH mixture used and material accumulated in rat tissues were previously reported (Barp et al. 2017a, 2017b). Rats were exposed to feed containing 0-4000 mg/kg broad MOSH mixture for 30, 60, 90 and 120 days; and for 120 days to feed containing different MOSH fractions: i) mainly molecular masses < C25 (S-C25), ii) dewaxed, mainly molecular masses > C25 (L-C25) and iii) the L-C25 fraction mixed with wax largely consisting of n-alkanes > C25 (L-C25W). Treatments related effects were increased liver and spleen weight, as well as vacuolization and granuloma formation with lymphoid cell clusters in the liver, but effects varied strongly between the MOSH fractions tested. We conclude that increased liver and spleen weights were related to accumulated n-alkanes (wax) above C25, presumably not relevant for humans, but also to MOSH from S-C25, mainly consisting of iso-alkanes and substituted cycloalkanes below C25 with a small proportion of n-alkanes. Induction of liver granuloma appeared to be related to n-alkanes > C25 and not to the accumulated amount of MOSH. Immune responses to an injected antigen were not affected. Iso-alkanes and substituted cycloalkanes accumulating in rat liver and spleen were similar to those accumulating in humans.

Gene expression profile in cases of infectious death in infancy.

BACKGROUND: Genetic predispositions in cases suffering sudden unexpected infant death have been a research focus worldwide during the past decade. Despite large efforts, there is still uncertainty concerning the molecular pathogenesis of these deaths. With genetic technology in constant development, the possibility of an alternative approach into this research field has become available, like mRNA expression studies. METHODS: In this study, we investigated mRNA gene expression in 14 cases who died suddenly and unexpectedly from infection without a history of severe illness prior to death. The control group included eight accidents, two cases of natural death, one undetermined, one case of medical malpractice, and two homicides. The study included tissue from liver, heart, and brain using Illumina whole-genome gene expression assay. RESULTS: From the array, 19 genes showed altered expression in the infectious deaths compared to controls. Tissue from the heart showed 15 genes with altered mRNA expression compared to the control group. CONCLUSIONS: Downregulation of KCNE5 in heart tissue from cases of infectious death was of particular interest. Variants of KCNE5 are associated with Brugada syndrome and sudden death and could be responsible for the fatal outcome in the group of infectious death. IMPACT: KCNE5 is downregulated in tissue from the heart in cases of infectious death in infancy. This study provides knowledge about the gene expression profile in cases of infectious death. Variants of a gene known to give increased risk of cardiac arrhythmia is downregulated in cases of infectious death in infancy. The results could give us better knowledge as to why some infants do not survive an infection. This study provides a candidate gene for future studies.

Death-scene investigations contribute to legal protection in unexpected child deaths in Norway.

AIM: This study reviewed cases of sudden unexpected child deaths in Norway to determine the significance of death-scene investigations (DSIs) in establishing cause and manner of death, and thereby it is relevance to legal protection. METHODS: Data from forensic autopsy reports and DSIs were collected and analysed for cases of unexpected deaths in children below 4 years of age in Norway during 2010-2016. RESULTS: Out of 141 cases, the death scene was investigated as a voluntary procedure in 75 cases and by the police in 41 cases. The cause of death remained unexplained in 81/141 (57%) of the cases, of which 46/141 (33%) met the criteria for sudden infant death syndrome (SIDS) or sudden unexplained death in early childhood (SUDC). The manner of death was determined in 102/141 (72%). Voluntary DSI increased the ability to rule out accidental suffocation, facilitated evaluations of environmental risk factors and enabled detection of possible neglect. CONCLUSION: Death-scene investigations illuminate uncertainty about the cause of death, especially in grey-area cases where accidental suffocation, neglect or abuse is suspected. Knowledge about the course of events and the cause of death enhances both the child's and the caregiver's legal protection. Death-scene investigations should therefore be mandatory.

Toxic effects of mineral oil saturated hydrocarbons (MOSH) and relation to accumulation in rat liver.

Humans are daily exposed to mineral oil saturated hydrocarbons (MOSH) from the diet. We exposed female Fischer 344 rats to a broad mixture and sub-fractions of MOSH. Chemical characterization of the MOSH mixture used and material accumulated in rat tissues were previously reported. Rats were exposed to feed containing 0-4000 mg/kg broad MOSH mixture for 30, 60, 90 and 120 days; and for 120 days to feed containing different MOSH fractions: i) mainly molecular masses < C25 (S-C25), ii) dewaxed, mainly molecular masses > C25 (L-C25) and iii) the L-C25 fraction mixed with wax largely consisting of n-alkanes > C25 (L-C25W). Treatments related effects were increased liver and spleen weight, as well as vacuolization and granuloma formation with lymphoid cell clusters in the liver, but effects varied strongly between the MOSH fractions tested. We conclude that increased liver and spleen weights were mainly related to accumulated iso-alkanes and substituted cycloalkanes, but also wax n-alkanes. Induction of liver granuloma appeared to be related to n-alkanes > C25 and not to the accumulated amount of MOSH. Immune responses to an injected antigen were not affected. MOSH fractions associated with increased liver and spleen weights were similar to those accumulating in humans.

Traceability and distribution of Neisseria meningitidis DNA in archived post mortem tissue samples from patients with systemic meningococcal disease.

BACKGROUND: The pathophysiology and outcome of meningococcal septic shock is closely associated with the plasma level of N. meningitidis lipopolysaccharides (LPS, endotoxin) and the circulating level of meningococcal DNA. The aim of the present study was to quantify the number of N. meningitidis in different formalin-fixed, paraffin-embedded (FFPE) tissue samples and fresh frozen (FF) tissue samples from patients with systemic meningococcal disease (SMD), to explore the distribution of N. meningitidis in the body. METHODS: DNA in FFPE and FF tissue samples from heart, lungs, liver, kidneys, spleen and brain from patients with meningococcal shock and controls (lethal pneumococcal infection) stored at variable times, were isolated. The bacterial load of N. meningitidis DNA was analyzed using quantitative real-time PCR (qPCR) and primers for the capsule transport A (ctrA) gene (1 copy per N. meningitidis DNA). The human beta-hemoglobin (HBB) gene was quantified to evaluate effect of the storage times (2-28 years) and storage method in archived tissue. RESULTS: N. meningitidis DNA was detected in FFPE and FF tissue samples from heart, lung, liver, kidney, and spleen in all patients with severe shock. In FFPE brain, N. meningitidis DNA was only detected in the patient with the highest concentration of LPS in the blood at admission to hospital. The highest levels of N. meningitidis DNA were found in heart tissue (median value 3.6 × 107 copies N. meningitidis DNA/µg human DNA) and lung tissue (median value 3.1 × 107 copies N. meningitidis DNA/µg human DNA) in all five patients. N. meningitidis DNA was not detectable in any of the tissue samples from two patients with clinical meningitis and the controls (pneumococcal infection). The quantity of HBB declined over time in FFPE tissue stored at room temperature, suggesting degradation of DNA. CONCLUSIONS: High levels of N. meningitidis DNA were detected in the different tissue samples from meningococcal shock patients, particularly in the heart and lungs suggesting seeding and major proliferation of meningococci in these organs during the development of shock, probably contributing to the multiple organ failure. The age of archived tissue samples appear to have an impact on the amount of quantifiable N. meningitidis DNA.

The gene encoding the inwardly rectifying potassium channel Kir4.1 may be involved in sudden infant death syndrome.

AIM: Disturbances in brain function and development may play a role in sudden infant death syndrome (SIDS). This Norwegian study aimed to test the hypothesis that specific variants of genes involved in water transport and potassium homeostasis would be predisposing factors for SIDS. METHODS: Genetic variation in the genes encoding aquaporin-4 (AQP4), Kir4.1 (KCNJ10) and α-syntrophin was analysed in 171 SIDS cases (62.6% male) with a median age of 15.5 (2-52) weeks and 398 adult controls (70.6% male) with a median age of 44 (11-91) years. All the subjects were Caucasians who were autopsied from 1988 to 2013. RESULTS: The CC genotype of rs72878794 in the AQP4 gene and a combination of the CC genotype in rs17375748, rs1130183, rs12133079 and rs1186688 in KCNJ10 (4xCC) were found to be associated with SIDS. The SIDS cases with the 4xCC SNP combination were younger than the SIDS cases with other genotype combinations (p = 0.006). CONCLUSION: This study indicates that genetic variations in KCNJ10 and AQP4 may be predisposing factors for SIDS. Alterations in the expression of the AQP4/Kir4.1 complex can disrupt water and ion homeostasis, which may influence brain development and facilitate brain oedema formation This may be especially unfavourable during the first weeks of life.

Altered gene expression and possible immunodeficiency in cases of sudden infant death syndrome.

BACKGROUND: A large number of studies have tried to uncover a genetic predisposition for sudden infant death syndrome (SIDS), but there is still uncertainty concerning the pathogenesis of these deaths. The purpose of this study was to investigate mRNA gene expression in SIDS cases and controls, in order to uncover genes that are differentially expressed in the two groups. METHODS: Tissue from brain, heart, and liver from 15 SIDS cases and 15 controls were included in the study, and mRNA expression was determined using the Illumina whole genome gene expression DASL HT assay. RESULTS: Seventeen genes showed significantly altered expression compared to controls, after correction for multiple testing. Three genes involved in the immune system were of particular interest, including the downregulation of MyD88 in tissue from SIDS brains, as well as the downregulation of the genes encoding CCL3 and UNC13 in the liver. CONCLUSION: These findings indicate that there is an altered expression of genes involved in the inflammatory process in a proportion of SIDS cases, which further strengthen the hypothesis that impaired immune response play a role in this syndrome.

Massive Organ Inflammation in Experimental and in Clinical Meningococcal Septic Shock.

Fulminant meningococcal sepsis is characterized by a massive growth of bacteria in the circulation, regarded as the primary inflammatory site, with no specific solid organ focus. Here we aimed to study the local inflammatory response in organs using a porcine model of fulminant meningococcal septic shock challenged with exponentially increasing doses of heat inactivated Neisseria meningitidis. The results were compared with those obtained in organs post mortem from three patients with lethal meningococcal septic shock. Nine patients with lethal pneumococcal disease and 14 patients with sudden infant death syndrome served as controls. Frozen tissue were thawed, homogenized and prepared for quantification of bacterial DNA by real-time polymerase chain reaction, and key inflammatory mediators were measured by ELISA in the pig material and by multiplex in the human material. In addition, gene expression assayed by Affymetrix gene expression profiling was performed in the pig study. The porcine model revealed a major influx of N. meningitidis in lungs, liver, spleen, and kidneys accompanied with major production of cardinal inflammatory mediators including tumor necrosis factor, interleukin (IL)-1ß, IL-6, and IL-8, far exceeding the amount detected in blood. Genes encoding for these mediators revealed a similar profile. By comparing the wild-type with a lipopolysaccharide (LPS) deficient meningococcal strain, we documented that LPS was the dominant group of molecules inducing organ inflammation and was required for IL-8 production. IL-10 production was predominantly stimulated by non-LPS molecules. The massive organ inflammation in the porcine model was present in the three patients dying of meningococcal shock and differed markedly from the patients with lethal pneumococcal infections and sudden infant death syndrome. In conclusion, in meningococcal sepsis, a massive local inflammatory response occurs in specific organs.

Genetic variation in the monoamine oxidase A and serotonin transporter genes in sudden infant death syndrome.

AIM: The purpose of this study was to investigate common polymorphisms in the genes encoding monoamine oxidase A (MAOA) and serotonin transporter (5-HTT) in Norwegian cases of sudden infant death syndrome (SIDS). This was done to further elucidate the role of genetic variation in these genes and SIDS. METHODS: A variable number of tandem repeat area in the promoter of the MAOA gene and rs25531 in the promoter region of the gene encoding 5-HTT were investigated in 193 SIDS cases and 335 controls. The methods used were polymerase chain reaction, restriction fragment analysis and gel electrophoresis. RESULTS: There were no differences between SIDS cases and controls for any of the investigated polymorphisms. This was also true when male and female SIDS cases were analysed separately. CONCLUSION: This article indicates that neither the VNTR in the promoter of the MAOA gene, nor rs25531 in the gene encoding 5-HTT, is involved in SIDS. However, as medullary serotonergic abnormalities most likely contribute to the death in at least some SIDS cases, it is important to investigate these genes, as well as other genes involved in the serotonergic network, in more detail.

Is there any correlation between HLA-DR expression in laryngeal mucosa and interleukin gene variation in sudden infant death syndrome?

AIM: The mucosal immune system and cytokines are activated in a large proportion of cases of sudden infant death syndrome (SIDS). Our aim was to search for a possible association between cytokine polymorphisms and immune stimulation of the laryngeal mucosal in SIDS. METHODS: HLA-DR expression in laryngeal mucosal glands and surface epithelium in 97 SIDS victims was evaluated applying a semi-quantitative scoring system. The findings were related to cytokine gene polymorphisms as well as to the level of various cytokines in the cerebrospinal fluid (CSF). A risk score was established: a score of 0 prepresenting negative HLA-DR, supine position and no fever prior to death. RESULTS: The IL-6 -176CG/CC genotype was found in 92.3% of the SIDS cases with positive score for all risk factors (p = 0.01). Infants with high HLA-DR score had high levels of IL-6 in the cerebrospinal fluid (>30 µg/L) (p = 0.005). Furthermore, the IL-8 SNPs -781 CT/TT genotypes and -251 AA/AT genotypes were observed in 93% of the SIDS cases with one or more of the risk factors present compared with SIDS cases no risk factors reported (p = 0.003 and p = 0.016, respectively). CONCLUSION: This study adds further evidence to the hypothesis that there are genetically associated disturbances of immunological homoeostasis in SIDS.

Forensic autopsies in a naturalistic setting in Norway: autopsy rates and toxicological findings.

Autopsies can give valuable information about the cause of death, and represent an important tool for obtaining valid cause of death statistics. In particular, they may shed light on the circumstances of death in ambiguous and criminal cases. To address the need for information on current autopsy practices, forensic autopsy rates in two counties in Central Norway over the period 2007-2009 were assessed. To investigate toxicological findings that could possibly remain undisclosed without the performance of an autopsy, the impact of alcohol and drugs in forensic autopsy cases from this material was evaluated. The total forensic autopsy rate in this material was 3%. The forensic autopsy rates were low for natural deaths (1%), accidental falls (12%) and the heterogeneous category "other accidents" (21%), relatively high for accidental poisonings (84%), and less than adequate for road traffic accidents (57%). For suicides the forensic autopsy rate was 63%, and for recognized homicides 100%. The total forensic autopsy rate was higher for men than for women (5% vs. 2%), and decreased with age, being 38% in the age group <30 years, 23% in the age group 30-59 years, and 1% in the age group >59 years. Despite that Norwegian legislation and regulations regarding forensic autopsy requests are national, the forensic autopsy rates were generally lower in the county of Nord-Trøndelag than in Sør-Trøndelag, with most striking differences in suicide deaths (11% vs. 91%) and road traffic accidents (46% vs. 67%). This illustrates how autopsy rates, and possibly cause of death registries, might be susceptible to the influence of regional variations in law enforcement, with possible consequences for the quality and validity of cause of death statistics. Of the forensic autopsy cases where toxicological analysis was performed (361 of 364 cases) a total of 71% had positive toxicology results; 12% were positive for alcohol only, 44% were positive for drugs only, and 15% were positive for both alcohol and drugs. The toxicology results suggest that alcohol and drugs are important factors in sudden unexpected deaths, and that a thorough and comprehensive toxicological analysis is called for when investigating these deaths. Mean BAC in alcohol positive forensic autopsy cases was 1.7‰ (median 1.6‰, range 0.29-4.1‰). The average number of substances detected in toxicology positive cases was 2.6 (median 2, range 1-10). The by far most frequently detected classes of substances were (1) benzodiazepines, (2) opioids and (3) alcohol.

Aquaporin-4 gene variation and sudden infant death syndrome.

The purpose of this study was to investigate the aquaporin-4 (AQP4) gene in cases of sudden infant death syndrome (SIDS) and controls and to elucidate the hypothesis that a genetically determined disturbed water homeostasis in the brain is involved as a predisposing factor in SIDS. The single nucleotide polymorphisms (SNPs) rs2075575, rs4800773, rs162004, and rs3763043 in the AQP4 gene were investigated in 141 SIDS cases and 179 controls. For each SIDS case, a brain/body weight ratio was calculated. The study revealed an association between the T allele and the CT/TT genotypes of rs2075575 and SIDS (C versus T, p < 0.01; CC versus CT/TT, p = 0.03). For the other three investigated SNPs, there were no differences in genotype frequencies between SIDS cases and controls. For the SNP rs2075575, it was also found an association between brain/body weight ratio and genotype in the SIDS cases aged 0.3-12 wk (p = 0.014, median ratio CC 10.6, CT/TT 12.1). In conclusion, this study indicates that rs2075575 may be of significance as a predisposing factor for SIDS, and that the CT/TT genotypes are associated with an increased brain/body weight ratio in infants dying from SIDS during the vulnerable period from birth up to 3 mo of age.

IL-1 gene cluster polymorphisms and sudden infant death syndrome.

Several studies indicate that interleukin gene polymorphisms are of importance to sudden infant death syndrome (SIDS), and so far it has been reported that associations between SIDS and polymorphism in the genes encoding tumor necrosis factor alpha, IL (interleukin)-6, and IL-10. IL-1 are important for the synthesis of acute phase proteins, and it is a pyrogen cytokine that may cause fever. The purpose of the present study was to investigate two polymorphisms in the IL-1alpha gene; a variable number of tandem repeat (VNTR) in intron 6 and a single nucleotide polymorphism in +4845G/T, as well as the -511C/T polymorphism in the gene encoding IL-1beta, and a VNTR in intron 2 of the competitive antagonist IL-1Ra, in SIDS cases, cases of infectious death, and controls. Furthermore, the genotypes were correlated with known external risk factors for SIDS. When investigating each polymorphism separately, no differences in genotype distribution between the diagnosis groups and controls were found. However, when combining VNTR and single nucleotide polymorphism genotypes, an association between the gene combination IL-1alpha VNTR A1A1/IL-1beta+ +4845TT and SIDS was disclosed (p < 0.01). In the SIDS group it was also found that the genotypes IL-1beta -511CC/CT were significantly more frequent in the SIDS victims found dead in a prone sleeping position, compared with SIDS victims found dead in other sleeping positions (p = 0.004). The findings in the present study indicate that specific interleukin gene variants may be a predisposing factor for sudden unexpected infant death.

Interleukin-6 and the serotonergic system of the medulla oblongata in the sudden infant death syndrome.

Mild infection may trigger sudden death in the vulnerable infant by cytokine interactions with a compromised medullary serotonergic (5-HT) system, leading to disrupted cardiorespiratory regulation and sleep-related sudden death. The cytokine interleukin (IL)-6 is elevated in the cerebrospinal fluid in SIDS. We tested the hypothesis that the expression of IL-6 receptors (IL-6R) and/or gp130 (involved in IL-6R signaling) is altered in the medullary 5-HT system in SIDS. Immunohistochemistry of IL-6R and gp130 was performed on medullae from 25 SIDS infants, 20 infectious deaths, and 14 controls using a semi-quantitative grading system. In the SIDS cases, mean IL-6R intensity grade in the arcuate nucleus (major component of medullary 5-HT system) was significantly higher than in the control group (2.00 +/- 0.07 vs. 1.77 +/- 0.08, P = 0.04), with no other differences in IL-6R or gp130 expression at any other site. Arcuate 5-HT neurons expressed IL-6R, indicating a site of IL-6/5-HT interaction. In SIDS, IL-6R expression is abnormal in the arcuate nucleus, the putative human homolog of rodent ventral medullary chemosensitivity sites involving 5-HT. Aberrant interactions between IL-6 and the arcuate nucleus may contribute to impaired responses to hypercapnia generated by infection (hyper-metabolism) combined with rebreathing.

Surfactant protein A and D gene polymorphisms and protein expression in victims of sudden infant death.

AIM: To investigate the innate immune components surfactant protein A (SP-A) and D (SP-D) in victims of sudden infant death syndrome (SIDS). METHODS: Ten common single nucleotide polymorphisms (SNPs) in the exons of SP-A1, SP-A2 and SP-D genes were analysed in 42 cases of SIDS and 46 explained sudden infant deaths. SP-A and SP-D protein expression in tissue from the aerodigestive tract was semi-quantitatively evaluated by immunohistochemistry. RESULTS: SP-D immunoreactivity was found in lungs and tissue from submandibular gland, palatine tonsils and duodenum. Positive SP-A immune staining was found exclusively in lung tissue. Neither the allele nor the haplotype distribution of the SP-A and SP-D genes was significantly different in SIDS compared to explained deaths. The most common SP-A haplotype, 6A2/1A0, tended to be overrepresented in the cases with low immunohistochemical SP-A expression (61%) compared to cases with high expression (49%), p = 0.08. The SP-D expression was not influenced by the 11 C/T or 160 A/G polymorphisms. CONCLUSION: No significant association between the common genetic variants of SP-A and SP-D and SIDS is disclosed by the present study. However, low SP-A protein expression may possibly be determined by the 6A2/1A0 SP-A haplotype, this should be subject for further investigation.

Helicobacter pylori antigen in stool is associated with SIDS and sudden infant deaths due to infectious disease.

Infection with Helicobacter pylori has been proposed to be a common cause of Sudden Infant Death Syndrome (SIDS). We investigated the frequency of H. pylori infection in 160 infant deaths and 156 live controls by means of the Helicobacter pylori stool antigen (HpSA) immunoassay. Histology was performed in 26 randomly selected cases. H. pylori antigen was detected in 8% (12/156) of the live controls compared with 25% (30/122) of SIDS cases (p < 0.001), 53% (9/17) of deaths due to infection (p < 0.001), and 9% (1/11) of accidental/violent deaths (p = 0.60). In the classic age peak for SIDS, 1-5 mo, 31% (21/67) of SIDS cases were HpSA positive compared with 1.5% (1/68) of live controls (p < 0.001). Rod-like immunoperoxidase positive H. pylori organisms were identified in 7/12 HpSA positive gastric antrum sections compared with 2/14 HpSA negative (p = 0.038). Significantly elevated IL-6 levels in cerebrospinal fluid representing signs of central immune stimulation were demonstrated in HpSA positive SIDS victims compared with HpSA negative victims (p = 0.045). Detection of H. pylori antigen in stool is associated with SIDS and deaths due to infections. We hypothesize that H. pylori infection in infancy may be involved as the triggering pathogen for sudden death during the first 5 month after birth.

TNF-alpha promoter polymorphisms in sudden infant death.

Several studies indicate that the immune system is stimulated in sudden infant death syndrome (SIDS). Tumor necrosis factor-alpha (TNF-alpha) is a proinflammatory cytokine that strongly affects the cytokine cascade. A genetic variant associated with high production of TNF-alpha may thus be of significance in the pathogenesis of SIDS. The purpose of the current study was to investigate possible relationships among the promoter polymorphisms -1031T/C, -857C/T, -308G/A, -244G/A, and -238G/A in the TNF-alpha gene and SIDS. The subjects investigated consisted of 148 SIDS cases, 56 borderline SIDS cases, 41 cases of infectious death, and 131 adult controls. When investigating each single nuclear polymorphism (SNP) separately, associations between -238GG and SIDS (p=0.022) and between -308GA and borderline SIDS (p=0.005) were found. There were no associations between any of the other SNPs investigated. Furthermore, a SNP profile was constructed by creating a genotype pattern from the investigated SNPs. Fifteen gene combinations were obtained, and 4 profiles had significantly different frequencies in SIDS cases and controls. The two SNP profiles -1031CT, -238GG, -857CC, -308GG and -1031TT, -238GG, -857CC, -308AA were found more often in SIDS and may thus be unfavorable. The findings add evidence to the theory that an unfavorable genetic profile in the TNF-alpha gene may be involved in SIDS by exposing the infant to both a high level of and prolonged exposure to TNF-alpha.

Serotonin transporter gene variation in sudden infant death syndrome.

AIM: To investigate polymorphisms in the serotonin transporter (5-HTT) gene in cases of sudden infant death syndrome (SIDS) and controls, and further to elucidate a possible relationship between 5-HTT genotypes and external risk factors for SIDS. METHOD: The subjects investigated consist of 163 SIDS cases and 243 controls. Polymorphisms in both the promoter and intron 2 of the 5-HTT gene were investigated, and the genotypes were determined using polymerase chain reaction (PCR) and gel electrophoresis. RESULTS: In the promoter, there was a tendency for the L allele and L/L genotype to be found more often in the SIDS cases than in the controls (p=0.05 and p=0.07, respectively). Regarding the intron 2 polymorphism, there were no differences between the groups, and the SIDS cases were not found to have a higher frequency of either the L/L-12/12 genotype or the L-12 haplotype than the controls. When investigating possible correlations between genotype and risk factors for SIDS, there was a tendency towards different distribution of the promoter genotypes in cases found dead prone compared to cases found dead in other sleeping positions (p=0.06). CONCLUSION: Polymorphisms in the promoter of the 5-HTT gene may be of importance with regard to SIDS.

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.

Post-neonatal drop in alveolar SP-A expression: biological significance for increased vulnerability to SIDS?

BACKGROUND: Surfactant protein A (SP-A) is synthesized in the lung and is a part of the innate immune system. The aim of this study was to evaluate the expression of SP-A in lung tissue from fetuses, infants, children and adults with special regard to sudden infant death syndrome (SIDS). METHODS: A total of 160 cases were studied; 19 fetuses and neonates, 59 SIDS and 49 explained infant deaths below 1 year of age, 19 toddlers and 14 adults. Immunohistochemical detection of SP-A using monoclonal antibodies was performed by microscopy of lung tissue specimens collected at autopsy. A scoring system was developed enabling semi-quantitative estimation of staining intensity and distribution. RESULTS: SP-A was detected in the terminal bronchioles and alveolar spaces of fetuses >35 weeks gestation. The intra-alveolar SP-A expression increased in the perinatal period followed by a marked drop in infants aged between 1 week and 5 months. Infants aged >5 months had abundant SP-A expression corresponding to older children and adults. There was no difference in the age distribution between cases of SIDS and explained deaths. CONCLUSIONS: The apparent drop in SP-A expression takes place in the first months after birth, corresponding with the classical age peak of SIDS. We therefore hypothesize that low expression of SP-A may be related in some as-yet undetermined way to the increased risk of SIDS at that age.