Mitochondrial tRNA genes and flanking regions in sudden infant death syndrome

Mitochondrial G8292A and C8794T mutations in patients with Niemann-Pick disease type C

Niemann-Pick disease type C (NP-C) is a neurovisceral lipid storage disorder. At the cellular level, the disorder is characterized by accumulation of unesterified cholesterol and glycolipids in the lysosomal/late endosomal system. NP-C is transmitted in an autosomal recessive manner and is caused by mutations in either the NPC1 (95% of families) or NPC2 gene. The estimated disease incidence is 1 in 120,000 live births, but this likely represents an underestimate, as the disease may be under-diagnosed due to its highly heterogeneous presentation. Variants of adenosine triphosphatase (ATPase) subunit 6 and ATPase subunit 8 (ATPase6/8) in mitochondrial DNA (mtDNA) have been reported in different types of genetic diseases including NP-C. In the present study, the blood samples of 22 Iranian patients with NP-C and 150 healthy subjects as a control group were analyzed. The DNA of the blood samples was extracted by the salting out method and analyzed for ATPase6/8 mutations using polymerase chain reaction sequencing. Sequence variations in mitochondrial genome samples were determined via the Mitomap database. Analysis of sequencing data confirmed the existence of 11 different single nucleotide polymorphisms (SNPs) in patients with NP-C1. One of the most prevalent polymorphisms was the A8860G variant, which was observed in both affected and non-affected groups and determined to have no significant association with NP-C incidence. Amongst the 11 polymorphisms, only one was identified in the ATPase8 gene, while 9 including A8860G were observed in the ATPase6 gene. Furthermore, two SNPs, G8292A and C8792A, located in the non-coding region of mtDNA and the ATPase6 gene, respectively, exhibited significantly higher prevalence rates in NP-C1 patients compared with the control group (P<0.01). The present study suggests that there may be an association between mitochondrial ATPase6/8 mutations and the incidence of NP-C disease. In addition, the mitochondrial SNPs identified maybe pathogenic mutations involved in the development and prevalence of NP-C. Furthermore, these results suggest a higher occurrence of mutations in ATPase6 than in ATPase8 in NP-C patients.

Mitochondrial deoxyribonucleic acid may play a role in a subset of sudden infant death syndrome cases

AIM

It has been suggested that progressive adenosine triphosphate (ATP) depletion could play a key role in sudden infant death syndrome (SIDS). Because mitochondrial deoxyribonucleic acid (mtDNA) codes for a subset of essential genes for oxidative phosphorylation, we investigated 22 mtDNA polymorphisms in a large sample of Caucasian SIDS cases.

METHODS

A total of 774 samples were analysed, 365 from infant SIDS cases (mean age 131 days) and 409 from controls. These were investigated for the presence of 22 haplogroup-specific single nucleotide polymorphisms (SNPs), using a SNaPshot assay, a mini-sequencing assay that combines polymerase chain reaction (PCR) and sequencing.

RESULTS

No significant differences in assigned haplogroups could be detected between the groups. With regard to gender and age, we found significant correlations for SNP positions 3010, 8251, 13 708, 14 470, 15 904 and 16 519. The most prominent result was the A allele in SNP 14 470 in male SIDS cases (p = 0.01).

CONCLUSION

This is the largest study on mtDNA polymorphisms in SIDS to date, and our results indicate that mtDNA may play a role in a subset of SIDS cases. In order to complement these significant results, it is important to consider nuclear gene coding for mitochondrial proteins in future studies.

Sarcomeric gene mutations in sudden infant death syndrome (SIDS)

In developed countries, sudden infant death syndrome (SIDS) represents the most prevalent cause of death in children between 1 month and 1 year of age. SIDS is a diagnosis of exclusion, a negative autopsy which requires the absence of structural organ disease. Although investigators have confirmed that a significant percentage of SIDS cases are actually channelopathies, no data have been made available as to whether other sudden cardiac death-associated diseases, such as hypertrophic cardiomyopathy (HCM), could be responsible for some cases of SIDS. The presence of a genetic mutation in the sarcomeric protein usually affects the force of contraction of the myocyte, whose weakness is compensated with progressive hypertrophy and disarray. However, it is unclear whether in the most incipient forms, that is, first years of life, the lack of these phenotypes still confers a risk of arrhythmogenesis. The main goal of the present study is to wonder whether genetic defects in the sarcomeric proteins, previously associated with HCM, could be responsible for SIDS. We have analysed 286 SIDS cases for the most common genes implicated in HCM in adults. A total of 680 mutations localised in 16 genes were analysed by semi-automated matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDITOF-MS) using the Sequenom MassARRAY(®) System. Ten subjects with completely normal hearts showed mutated alleles at nine of the genetic variants analysed, and one additional novel mutation was detected by conventional sequencing. Therefore, a genetic mutation associated with HCM may cause sudden cardiac death in the absence of an identifiable phenotype.

Molecular Investigations of Sudden Unexplained Deaths

Sudden unexplained deaths in apparently healthy individuals (newborn through adult) pose a vexing challenge to medical examiners, law enforcement and society as a whole. Recent advances in “molecular autopsies” have begun to uncover the mystery surrounding sudden unexplained deaths by identifying mutations that can result in or predispose an apparently healthy individual to sudden death. Genetic risks of sudden unexplained deaths have been studied from several different perspectives, and categorized generally by systems, including: cardiac, nervous, immune, and metabolic. This article reviews the genetic risks in sudden unexplained deaths, presents the current state and challenges of molecular investigations, and sheds light on future directions in sudden unexplained death investigations.

Gene variants predisposing to SIDS: current knowledge

Genetic risk factors play a role in sudden unexpected infant death; either as a cause of death, such as in cases with medium-chain acyl-coenzyme A dehydrogenase deficiency and cardiac arrest due to long QT syndrome, or as predisposing factors for sudden infant death syndrome (SIDS). Most likely genetic predisposition to SIDS represent a polygenic inheritance pattern leading to sudden death when combined with other risk factors, such as a vulnerable developmental stage of the central nervous system and/or the immune system, in addition to environmental risk factors, such as a common cold or prone sleeping position. Genes involved in the regulation of the immune system, cardiac function, the serotonergic network and brain function and development have so far emerged as the most important with respect to SIDS. The purpose of the present paper is to survey current knowledge on SIDS and possible genetic contributions.

Sudden infant death syndrome (SIDS) in African Americans: polymorphisms in the gene encoding the stress peptide pituitary adenylate cyclase-activating polypeptide (PACAP)

AIMS

Mice lacking pituitary adenylate cyclase-activating polypeptide (PACAP) are prone to sudden death in the second post-natal week, having respiratory and metabolic disturbances reminiscent of the human Sudden Infant Death Syndrome (SIDS). Here we test the hypothesis that the human PACAP gene is a site of genetic variance associated with SIDS in a cohort of 92 victims and 92 matched controls.

METHODS

Using polymerase chain reaction and sequencing, we examined the PACAP gene in 92 SIDS cases (46 Caucasians and 46 African Americans) and 92 race- and gender-matched controls.

RESULTS

We found no significant associations between PACAP and SIDS in Caucasians. However, in the African Americans, a non-synonymous single nucleotide polymorphism (i.e. an aspartic acid/glycine coding variant, rs2856966) within exon 2 of PACAP was significantly associated with SIDS (p = 0.004), as were haplotypes containing this polymorphism (p < 0.0001). Glycine was three times more likely at this location in the African-American SIDS victims (17 cases) than African-American controls (5 cases).

CONCLUSION

These data are the first to suggest an association between a variant within the coding region of the PACAP gene and SIDS. Based on these findings, further investigations are warranted into the functional importance of PACAP signaling in neonatal survival and the role of PACAP-signaling abnormalities in SIDS.

Sudden infant death syndrome: another year of new hope but no cure

PURPOSE OF REVIEW

Sudden infant death syndrome has inspired increasingly sophisticated studies at a time when rates are declining because of the Back-to-Sleep campaign, but ethnic disparities are widening. This review evaluates and discusses original, recent research in this area.

RECENT FINDINGS

The epidemiology of sudden infant death syndrome was evaluated, corroborating known risk factors and identifying new risk factors such as socioeconomic depression and air pollution. Deficits in our understanding of risk factors for this syndrome persist, suggesting a need for ethnicity-specific education, especially among the underserved. Both autopsy and genetic testing were found to improve diagnostic accuracy or identify other causes of death (e.g. long Q-T syndrome). Debate persists over counseling regarding pacifiers and co-sleeping within the context of breastfeeding. Support was found for a relationship between sudden infant death syndrome and autonomic dysregulation via the serotonergic pathway, but more research is needed.

SUMMARY

The cause of sudden infant death syndrome remains elusive. Recent studies, however, suggest that improved culturally sensitive educational programs, increased diagnostic specificity, and further clarification of the link between genetics and developmental stage might further decrease the number of infants lost to this devastating disease and elucidate the mechanism(s) responsible for this syndrome.