Molecular autopsy

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DNA structure

Molecular autopsy or postmortem molecular testing is a set of molecular techniques used in forensic medicine to attempt to determine the cause of death in unexplained cases, in particular sudden unexplained deaths (for example sudden cardiac death). About 30% of sudden cardiac deaths in young people are not explained after full conventional autopsy, and are classified as sudden unexplained deaths. The use of a panel of genetic markers for long QT syndrome, catecholaminergic polymorphic ventricular tachycardia and cardiac channel miopathies elucidated around 40 to 45% of the cases. [1]

Contents

Ethics

In today’s day and age the use of Molecular Autopsy has come with its share of ethical issues. The issues are raised because there are no set laws that a Medical Examiner must follow. For instance it is not required for an examiner to get permission from a relative to go forth with a molecular autopsy. This has created many issues for families because they may not always want to know the results of why a loved one died. Knowing this information can create anxiety and concern for family members over a possible mutation of their own gene that could cause their death, while they would have no way of stopping it. It also creates an issue because with most if not all examinations, samples of a test are retained in a lab. This means the tests from a loved one is saved forever, to be possibly used in a different experiment. The family usually has no say on whether this will happen or not.

The problem that arises for medical examiners is that if an examination is done and the lives of family members could be at risk, they have no authorization to tell the family if they do not wish to know. Some examiners believe that this is against their duty as a professional doctor. For example, it has been estimated that 30% of young sudden cardiac deaths can be traced to being inherited. So doctors feel that it is against their profession to not let someone know when they could be at risk. [2]

Methods

When a traditional medical autopsy is not able to determine the sudden cause of death, molecular autopsy may help provide an alternative insight through the use of Deoxyribonucleic acid (DNA) sequencing. It looks at things from a cellular level instead of only what the human eye can see.

The first step in performing a molecular autopsy is to obtain a sample of blood or tissue from the individual after death has occurred. DNA is then extracted from the blood sample in order to undergo a process of genetic sequencing. Then, the DNA sequence is carefully analyzed to detect any gene mutations that may be a cause of sudden death. Initially, molecular autopsy focused on the direct DNA sequencing of four genes. However, recent advancements in sequencing technologies have made it possible to screen a large number of genes at once from a small sample of DNA through whole-exome sequencing (WES) in which the coding regions of all 22,000 genes are sequenced. This potentially allows the detection of genetic variants of genes related to all major diseases. [3]

Case Studies

A study of sudden death brought a mother to once question whether her thirteen-year-old son has what previously killed her seventeen-year-old son. This son had been found lying in bed dead with an autopsy that was inconclusive. Many blamed it on drug use and abuse, but that was really not the cause.

PQRST complex of a heart beat SinusRhythmLabels.svg
PQRST complex of a heart beat

Almost half the sudden deaths of previously healthy children have no findings on autopsy. These children are referred to as having sudden unexplained death syndrome (SUDS). In the Olmsted County population study, six of the twelve cases died of unknown causes of SUDS. A lot of forensic pathologists blame a fatal arrhythmia of the heart to be the cause of SUDS due to the lethal disorders like long QT syndrome (LQTS). This is a prolonged QT interval in the heart’s natural rhythm. This is can leave no trace for an autopsy. The clinical signs of LQTS are syncope, seizures, or sudden death.

In England there are around 200 SUDS cases yearly, and nearly a third of those were blamed on LQTS. This however, cannot be proved without an electrocardiogram before death.

By looking at the molecular level of the issues that cause SUDS and/or LQTS, they may be able to find the ion channels that are cardiac defective. There are six LQTS genetic markers, five LQTS genes, and around 200 mutations identified all in patients with LQTS. By targeting these molecules, molecular autopsy can be possible. This is how molecular autopsy is relevant in all three of the following cases.

Case 1

In this case of the mother with questions of her living son possible having the same issue that her now dead son had, there was a history of these LQTS clinical signs that were stated above in the family. Specifically, the grandmother had syncopal episodes multiple times. Although, multiple electrocardiograms showed no significant findings that would lead to a diagnosis of LQTS.

There were multiple studies done, one in particular was the epinephrine-triggered alterations in repolarization. This showed the results of having five nucleotides (guanine [g], cytosine [c], guanine, cytosine, and thymidine [t]) from positions 735 - 739 were not present. These are the genetic components of DNA. This resulted in the cardiac potassium channel to cause a shift of amino acids. This shift is where the stop codon at an amino acid is introduced and needed. This can severely impact the depolarization and repolarization of the heart, which is crucial for the normal rhythm of the muscle. [4]

Case 2

Another study was done for molecular autopsy on the RyR2-encoded cardiac ryanodine receptor in SUDS. There were 49 cases in this study, 30 of which were male. Thirteen of the 49 studied had a family history of syncope. In seven of these cases of SUDS, there were six distinct RyR2 missense mutations. During these deaths, the activities were as follows: three cases of exertion, one case of emotion, and three unknown cases. This study was of the first on RyR2 in molecular autopsy. It targeted 18 of the 105 protein-encoding exons of the cardiac ryanodine receptor/calcium release channel. This revealed one in every seven to be positive for the RyR2 mutations in SUDS. This studied showed that testing of this mutation should be a part of the autopsy investigation. This study also proved that this mutation is possibly inheritable. [5]

Case 3

Another study is the pharmacogenomics as molecular autopsy for forensic toxicology. This study is looking at the genotyping of cytochrome P450 3A4*1B and 3A5*3. Pharmacogenetics is the study of genetic contributions to drug action. This can help in certifying a fentanyl toxicity. Fentanyl is used for anesthesia in surgery or pain control/management in animals and humans. This drug can have variable metabolisms due to the different alleles in the cytochrome P450. This study looked at 25 different fentanyl related deaths (22 caucasians, 1 African American, and 2 Native Americans). from the Milwaukee county medical Examiner’s office and referrals. Blood was taken and analyzed after death by radioimmunoassay and liquid chromatography/mass spectrometry. This study showed the average fentanyl concentration in CYP3A4*1B wild type and 3A5*3 homozygous variant cases were higher than those of the CYP3A4*1B variant cases (this was not a significant difference). The data taken from this study gave scientific evidence that CYP3A5 is involved in the fentanyl metabolism, where as the homozygous CYP3A5*3 causes impaired metabolism of fentanyl. Genotyping CYP3A4*1B and 3A5*3 variants may help to certify the fentanyl toxicity. For further studying of this subject, there will be more cases needed. This study was mainly to supply information for this drug monitoring and pain management. [6]

Relationship with molecular autopsy

Molecular autopsy has become a huge component in the investigation process of SUD, specifically sudden cardiac death (SCD). The causes of SCD range widely but the greatest contributor to SCD is an underlying genetic predisposition, especially in those under the age of 40. The inherited diseases include, but are not limited to, primary arrythmogenic disorders and inherited cardiomyopathies. Molecular autopsy not only helps identify an explanation for SUD, but evaluates the potential risks that relatives may have in relation to cardiovascular disease. Over 3 million people die of SCD a year, making molecular autopsy for SCD in high demand. Using molecular autopsy for SCD in the young, fit, and seemingly healthy individual is an increasingly interesting topic for research. Up to 30% of the autopsies given post-mortem to young individuals who die of SCD have no cause of death identified, called autopsy-negative or sudden arrhythmic death syndrome (SADS). This is because many primary arrhythmogenic disorders do not cause structural damage to the heart, making it difficult for pathologists to draw a conclusion on the cause of death.

Genetic testing for SADS cases started over ten years ago. A sample of the cadaver’s blood is taken and tested. The molecular autopsy focuses on four main genes: KCNQ1, KCNH2, SCN5A, and RYR2. Greater than 95% of the mutations found in the molecular autopsy are a chromosome dominant trait, indicating that half of the children to the tested individual also carry the mutated gene. [7]

Related Research Articles

A microsatellite is a tract of repetitive DNA in which certain DNA motifs are repeated, typically 5–50 times. Microsatellites occur at thousands of locations within an organism's genome. They have a higher mutation rate than other areas of DNA leading to high genetic diversity. Microsatellites are often referred to as short tandem repeats (STRs) by forensic geneticists and in genetic genealogy, or as simple sequence repeats (SSRs) by plant geneticists.

<span class="mw-page-title-main">Brugada syndrome</span> Heart conduction disease

Brugada syndrome (BrS) is a genetic disorder in which the electrical activity of the heart is abnormal due to channelopathy. It increases the risk of abnormal heart rhythms and sudden cardiac death. Those affected may have episodes of syncope. The abnormal heart rhythms seen in those with Brugada syndrome often occur at rest. They may be triggered by a fever.

<span class="mw-page-title-main">Long QT syndrome</span> Medical condition

Long QT syndrome (LQTS) is a condition affecting repolarization (relaxing) of the heart after a heartbeat, giving rise to an abnormally lengthy QT interval. It results in an increased risk of an irregular heartbeat which can result in fainting, drowning, seizures, or sudden death. These episodes can be triggered by exercise or stress. Some rare forms of LQTS are associated with other symptoms and signs including deafness and periods of muscle weakness.

<span class="mw-page-title-main">Sarcoplasmic reticulum</span> Menbrane-bound structure in muscle cells for storing calcium

The sarcoplasmic reticulum (SR) is a membrane-bound structure found within muscle cells that is similar to the smooth endoplasmic reticulum in other cells. The main function of the SR is to store calcium ions (Ca2+). Calcium ion levels are kept relatively constant, with the concentration of calcium ions within a cell being 10,000 times smaller than the concentration of calcium ions outside the cell. This means that small increases in calcium ions within the cell are easily detected and can bring about important cellular changes (the calcium is said to be a second messenger). Calcium is used to make calcium carbonate (found in chalk) and calcium phosphate, two compounds that the body uses to make teeth and bones. This means that too much calcium within the cells can lead to hardening (calcification) of certain intracellular structures, including the mitochondria, leading to cell death. Therefore, it is vital that calcium ion levels are controlled tightly, and can be released into the cell when necessary and then removed from the cell.

<span class="mw-page-title-main">Arrhythmogenic cardiomyopathy</span> Medical condition

Arrhythmogenic cardiomyopathy (ACM), arrhythmogenic right ventricular dysplasia (ARVD), or arrhythmogenic right ventricular cardiomyopathy (ARVC), most commonly is an inherited heart disease.

<span class="mw-page-title-main">Frameshift mutation</span> Mutation that shifts codon alignment

A frameshift mutation is a genetic mutation caused by indels of a number of nucleotides in a DNA sequence that is not divisible by three. Due to the triplet nature of gene expression by codons, the insertion or deletion can change the reading frame, resulting in a completely different translation from the original. The earlier in the sequence the deletion or insertion occurs, the more altered the protein. A frameshift mutation is not the same as a single-nucleotide polymorphism in which a nucleotide is replaced, rather than inserted or deleted. A frameshift mutation will in general cause the reading of the codons after the mutation to code for different amino acids. The frameshift mutation will also alter the first stop codon encountered in the sequence. The polypeptide being created could be abnormally short or abnormally long, and will most likely not be functional.

<span class="mw-page-title-main">Jervell and Lange-Nielsen syndrome</span> Medical condition

Jervell and Lange-Nielsen syndrome (JLNS) is a rare type of long QT syndrome associated with severe, bilateral sensorineural hearing loss. Those with JLNS are at risk of abnormal heart rhythms called arrhythmias, which can lead to fainting, seizures, or sudden death. JLNS, like other forms of long QT syndrome, causes the cardiac muscle to take longer than usual to recharge between beats. It is caused by genetic variants responsible for producing ion channels that carry transport potassium out of cells. The condition is usually diagnosed using an electrocardiogram, but genetic testing can also be used. Treatment includes lifestyle measures, beta blockers, and implantation of a defibrillator in some cases. It was first described by Anton Jervell and Fred Lange-Nielsen in 1957.

<span class="mw-page-title-main">Romano–Ward syndrome</span> Medical condition

Romano–Ward syndrome is the most common form of congenital Long QT syndrome (LQTS), a genetic heart condition that affects the electrical properties of heart muscle cells. Those affected are at risk of abnormal heart rhythms which can lead to fainting, seizures, or sudden death. Romano–Ward syndrome can be distinguished clinically from other forms of inherited LQTS as it affects only the electrical properties of the heart, while other forms of LQTS can also affect other parts of the body.

Ryanodine receptors form a class of intracellular calcium channels in various forms of excitable animal tissue like muscles and neurons. There are three major isoforms of the ryanodine receptor, which are found in different tissues and participate in different signaling pathways involving calcium release from intracellular organelles. The RYR2 ryanodine receptor isoform is the major cellular mediator of calcium-induced calcium release (CICR) in animal cells.

<span class="mw-page-title-main">Genetic analysis</span>

Genetic analysis is the overall process of studying and researching in fields of science that involve genetics and molecular biology. There are a number of applications that are developed from this research, and these are also considered parts of the process. The base system of analysis revolves around general genetics. Basic studies include identification of genes and inherited disorders. This research has been conducted for centuries on both a large-scale physical observation basis and on a more microscopic scale. Genetic analysis can be used generally to describe methods both used in and resulting from the sciences of genetics and molecular biology, or to applications resulting from this research.

Sudden unexpected death in epilepsy (SUDEP) is a fatal complication of epilepsy. It is defined as the sudden and unexpected, non-traumatic and non-drowning death of a person with epilepsy, without a toxicological or anatomical cause of death detected during the post-mortem examination.

<span class="mw-page-title-main">Catecholaminergic polymorphic ventricular tachycardia</span> Medical condition

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited genetic disorder that predisposes those affected to potentially life-threatening abnormal heart rhythms or arrhythmias. The arrhythmias seen in CPVT typically occur during exercise or at times of emotional stress, and classically take the form of bidirectional ventricular tachycardia or ventricular fibrillation. Those affected may be asymptomatic, but they may also experience blackouts or even sudden cardiac death.

<span class="mw-page-title-main">Ryanodine receptor 2</span> Transport protein and coding gene in humans

Ryanodine receptor 2 (RYR2) is one of a class of ryanodine receptors and a protein found primarily in cardiac muscle. In humans, it is encoded by the RYR2 gene. In the process of cardiac calcium-induced calcium release, RYR2 is the major mediator for sarcoplasmic release of stored calcium ions.

<span class="mw-page-title-main">FKBP1B</span> Protein-coding gene in the species Homo sapiens

Peptidyl-prolyl cis-trans isomerase FKBP1B is an enzyme that in humans is encoded by the FKBP1B gene.

<span class="mw-page-title-main">Ankyrin-2</span> Protein-coding gene in the species Homo sapiens

Ankyrin-2, also known as Ankyrin-B, and Brain ankyrin, is a protein which in humans is encoded by the ANK2 gene. Ankyrin-2 is ubiquitously expressed, but shows high expression in cardiac muscle. Ankyrin-2 plays an essential role in the localization and membrane stabilization of ion transporters and ion channels in cardiomyocytes, as well as in costamere structures. Mutations in ANK2 cause a dominantly-inherited, cardiac arrhythmia syndrome known as long QT syndrome 4 as well as sick sinus syndrome; mutations have also been associated to a lesser degree with hypertrophic cardiomyopathy. Alterations in ankyrin-2 expression levels are observed in human heart failure.

<span class="mw-page-title-main">Exome sequencing</span> Sequencing of all the exons of a genome

Exome sequencing, also known as whole exome sequencing (WES), is a genomic technique for sequencing all of the protein-coding regions of genes in a genome. It consists of two steps: the first step is to select only the subset of DNA that encodes proteins. These regions are known as exons—humans have about 180,000 exons, constituting about 1% of the human genome, or approximately 30 million base pairs. The second step is to sequence the exonic DNA using any high-throughput DNA sequencing technology.

<span class="mw-page-title-main">Sudden arrhythmic death syndrome</span> Medical condition

Sudden arrhythmic death syndrome (SADS) is a sudden unexpected death of adolescents and adults, mainly during sleep. One relatively common type is known as Brugada syndrome.

JTV-519 (K201) is a 1,4-benzothiazepine derivative that interacts with many cellular targets. It has many structural similarities to diltiazem, a Ca2+ channel blocker used for treatment of hypertension, angina pectoris and some types of arrhythmias. JTV-519 acts in the sarcoplasmic reticulum (SR) of cardiac myocytes by binding to and stabilizing the ryanodine receptor (RyR2) in its closed state. It can be used in the treatment of cardiac arrhythmias, heart failure, catecholaminergic polymorphic ventricular tachycardia (CPVT) and store overload-induced Ca2+ release (SOICR). Currently, this drug has only been tested on animals and its side effects are still unknown. As research continues, some studies have also found a dose-dependent response; where there is no improvement seen in failing hearts at 0.3 μM and a decline in response at 1 μM.

<span class="mw-page-title-main">Celivarone</span> Experimental drug being tested for use in pharmacological antiarrhythmic therapy

Celivarone is an experimental drug being tested for use in pharmacological antiarrhythmic therapy. Cardiac arrhythmia is any abnormality in the electrical activity of the heart. Arrhythmias range from mild to severe, sometimes causing symptoms like palpitations, dizziness, fainting, and even death. They can manifest as slow (bradycardia) or fast (tachycardia) heart rate, and may have a regular or irregular rhythm.

Masonic Medical Research Institute (MMRI) is a non-profit medical research center located in Utica, New York. The institute studies experimental cardiology with an emphasis on cardiac arrhythmias, ischemic heart disease and sudden cardiac death. Research topics also include autism, Noonan Syndrome, brown fat, nano-imaging, targeted drug delivery, and more. There are five Principal Investigators at MMRI, each with their own lab, team, and area of study. The Institute's research and staff are independent, but MMRI gets its name from its original funding in 1958 by the Masonic Grand Lodge of New York.

References

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  2. McGuire, Amy L., Quianta Moore, Mary Majumder, Magdalena Walkiewicz, Christine M. Eng, John W. Belmont, Salma Nassef, Sandra Darilek, Katie Rutherford, Stacey Pereira, Steven E. Scherer, V. Reid Sutton, Dwayne Wolf, Richard A. Gibbs, Roger Kahn, Luis A. Sanchez, and The Molecular Autopsy Consortium of Houston (MATCH). "The Ethics of Conducting Molecular Autopsies in Cases of Sudden Death in the Young." The Ethics of Conducting Molecular Autopsies in Cases of Sudden Death in the Young (2016): n. pag. Genome Research. Cold Spring Harbor Laboratory Press, Sept. 2016. Web. 21 Apr. 2017.
  3. Lahrouchi, Najim, Elijah R. Behr, and Connie R. Bezzina. “Next-Generation Sequencing in Post-Mortem Genetic Testing of Young Sudden Cardiac Death Cases.” Frontiers in Cardiovascular Medicine 3 (2016): 13. PMC. Web. 2 Apr. 2017.
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  5. Tester, David J., BS, Daniel B. Spoon, BS, Hector H. Valdivia, MD, PhD, Jonathan C. Makelski, MD, and Michael J. Ackerman, MD, PhD. "Targeted Mutational Analysis of the RyR2-Encoded Cardiac Ryanodine Receptor in Sudden Unexplained Death: A Molecular Autopsy of 49 Medical Examiner/Coroner's Cases." May Clinic Proceedings. N.p., 2004. Web.
  6. Jin, Ming, Susan B. Gock, Paul J. Jannetto, Jeffrey M. Jentzen, and Steven H. Wong. "Pharmacogenomic as Molecular Autopsy for Forensic Toxicology: Genotyping Cytochrome P450 3A4*1B and 3A5*3 for 25 Fentanyl Cases." Journal of Analytical Toxicology. N.p., 2005. Web.
  7. Semsarian, Christopher, and Robert M. Hamilton. (2012) "Key Role of the Molecular Autopsy in Sudden Unexpected Death." Heart Rhythm 9.1: 145-50. doi: 10.1016/j.hrthm.2011.07.034. Semsarian, C., Ingles, J. and Wilde, A.A. (2015) Sudden Cardiac Death in the Young: The Molecular Autopsy and a Practical Approach to Surviving Relatives. European Heart Journal, 36 (21), 1290-1296. Doi: 10.1093/eurheartj/ehv063