Metabolic autopsy with postmortem cultured fibroblasts in sudden unexpected death in infancy: diagnosis of mitochondrial respiratory chain disorders

Molecular autopsy for sudden death in Japan

Japan has various death investigation systems; however, external examinations, postmortem computed tomography, macroscopic examinations, and microscopic examinations are performed regardless of the system used. These examinations can reveal morphological abnormalities, whereas the cause of death in cases with non-morphological abnormalities can be detected through additional examinations. Molecular autopsy and postmortem genetic analyses are important additional examinations. They are capable of detecting inherited arrhythmias or inherited metabolic diseases, which are representative non-morphological disorders that cause sudden death, especially in infants and young people. In this review, we introduce molecular autopsy reports from Japan and describe our experience with representative cases. The relationships between drug-related deaths and genetic variants are also reviewed. Based on the presented information, molecular autopsy is expected to be used as routine examinations in death investigations because they can provide information to save new lives.

Accurate interpretation of genetic variants in sudden unexpected death in infancy by trio-targeted gene-sequencing panel analysis

In sudden unexpected death in infancy cases, postmortem genetic analysis with next-generation sequencing potentially can extract candidate genes associated with sudden death. However, it is difficult to accurately interpret the clinically significant genetic variants. The study aim was to conduct trio analysis of cases of sudden unexpected death in infancy and their parents to more accurately interpret the clinically significant disease-associated gene variants associated with cause of death. From the TruSight One panel targeting 4813 genes we extracted candidate genetic variants of 66 arrhythmia-, 63 inherited metabolic disease-, 81 mitochondrial disease-, and 6 salt-losing tubulopathy-related genes in 7 cases and determined if they were de novo or parental-derived variants. Thirty-four parental-derived variants and no de novo variants were found, but none appeared to be related to the cause of death. Using trio analysis and an in silico algorithm to analyze all 4813 genes, we identified OBSCN of compound heterozygous and HCCS of hemizygous variants as new candidate genetic variants related to cause of death. Genetic analysis of these deceased infants and their living parents can provide more accurate interpretation of the clinically significant genetic variants than previously possible and help confirm the cause of death.

Generation of three induced pluripotent stem cell lines from postmortem tissue derived following sudden death of a young patient with STXBP1 mutation

We established three iPSC lines from postmortem-cultured fibroblasts derived following the sudden unexpected death of an 8-year-old girl with Lennox-Gastaut syndrome, who turned out to have the R551H-mutant STXBP1 gene. These iPSC clones showed pluripotent characteristics while retaining the genotype and demonstrated trilineage differentiation capability, indicating their utility in disease-modeling studies, i.e., STXBP1-encephalopathy. This is the first report on the establishment of iPSCs from a sudden death child, suggesting the possible use of postmortem-iPSC technologies as an epoch-making approach for precise identification of the cause of sudden death.

Metabolic autopsy with next generation sequencing in sudden unexpected death in infancy: Postmortem diagnosis of fatty acid oxidation disorders

The recent introduction of metabolic autopsy in the field of forensic science has made it possible to detect hidden inherited metabolic diseases. Since the next generation sequencing (NGS) has recently become available for use in postmortem examinations, we used NGS to perform metabolic autopsy in 15 sudden unexpected death in infancy cases. Diagnostic results revealed a case of carnitine palmitoyltransferase II deficiency and some cases of fatty acid oxidation-related gene variants. Metabolic autopsy performed with NGS is a useful method, especially when postmortem biochemical testing is not available.

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This is the first metabolic autopsy performed with next generation sequencing (NGS).

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We detected one case of CPT II deficiency and three cases of FAOD-related rare variants.

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Some of them had no specific abnormality except for genetic variants.

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These cases would be undetected without NGS.

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We advocate metabolic autopsy performed with NGS.

A pathologist׳s perspective on the perinatal autopsy

The perinatal autopsy is an important tool in the investigation of fetal and neonatal death, and a complete understanding of its risks and benefits is necessary for providers of perinatal care. This review, from the perspective of a perinatal pathologist, reports the details of the autopsy procedure, its goals, its value to individual patients and the health care system in general, and its alternatives. Even with new emerging technologies, the conventional perinatal autopsy remains the gold standard for determining the cause of death and the final summary of all pathologic findings. Therefore, the information provided in this review can help providers properly convey information about perinatal autopsy to bereaved families.

Molecular diagnosis of mitochondrial respiratory chain disorders in Japan: focusing on mitochondrial DNA depletion syndrome

BACKGROUND

Although mitochondrial respiratory chain disorders (MRCD) are one of the most common congenital metabolic diseases, there is no cumulative data on enzymatic diagnosis and clinical manifestation for MRCD in Japan and Asia.

METHODS

We evaluated 675 Japanese patients having profound lactic acidemia, or patients having symptoms or signs of multiple-organ origin simultaneously without lactic acidemia on respiratory chain enzyme activity assay and blue native polyacrylamide gel electrophoresis. Quantitative polymerase chain reaction was used to diagnose mitochondrial DNA depletion syndrome (MTDPS). Mutation analysis of several genes responsible for MTDPS was also performed.

RESULTS

A total of 232 patients were diagnosed with a probable or definite MRCD. MRCD are common, afflicting one in every several thousand people in Japan. More than one in 10 of the patients diagnosed lacked lactic acidemia. A subsequent analysis of the causative genes of MTDPS identified novel mutations in six of the patients. A 335 bp deletion in deoxyguanosine kinase (DGUOK; g.11692_12026del335 (p.A48fsX90)) was noted in two unrelated families, and may therefore be a common mutation in Japanese people. The proportion of all patients with MTDPS, and particularly those with recessive DNA polymerase γ (POLG) mutations, appears to be lower in Japan than in other studies. This is most likely due to the relatively high prevalence of ancient European POLG mutations in Caucasian populations. No other significant differences were identified in a comparison of the enzymatic diagnoses, disease classifications or prognoses in Japanese and Caucasian patients with MRCD.

CONCLUSION

MTDPS and other MRCD are common, but serious, diseases that occur across all races.