Forensic SNP Genotyping with SNaPshot: Development of a Novel In-house SBE Multiplex SNP Assay,

A method of identifying the high-risk mutations of sudden cardiac death at KCNQ1 and KCNH2 genes

Sudden Cardiac Death (SCD) often shows negative anatomy results after a systemic autopsy and the gene mutations of potassium channel play a key role in the etiology of SCD. We established a feasible system to detect SCD-related mutations and investigated the mutations at KCNQ1 and KCNH2 genes in the Chinese population. We established a mutation detection system combined with multiplex PCR, SNaPshot technique, and capillary electrophoresis. We genotyped 101 putative mutations at KCNQ1 and KCNH2 genes in 60 SCD of negative anatomy and 50 controls using the established assay and compared Odd Ratio (OR). Four coding variants were identified in the KCNQ1 gene: S546S, I145I, P448R, and G643S. The mutations of I145I and S546S did not differ significantly in the SCD compared with controls. 21 SCD individuals (35 %) and 1 control individual (2 %) showed a genotype of C/G at P448R (OR = 17.5, 95 % CI [2.40-127.82]). 24 SCD individuals (40 %) and 1 control individual (2 %) showed a genotype of C/G at G643S (OR = 20.0, 95 % CI [2.75-145.25]). We established a robust assay for rapid screening the putative SCD-related mutations in KCNQ1 and KCNH2 genes. The new assay in our study is easily amenable to the majority of laboratories without the need for new specialized equipment. Our method will meet the increasing requirement of mutation screening for SCD in regular DNA laboratories and will help screen mutations in those dead of SCD and their relatives.

Age estimation using DNA methylation technique in forensics: a systematic review

Background

In addition to the DNA sequence, epigenetic markers have become substantial forensic tools during the last decade. Estimating the age of an individual from human biological remains may provide information for a forensic investigation. Age estimation in molecular strategies can be obtained by telomere length, mRNa mutation, or by sjTRECs but the accuracy is not sufficient in forensic practice because of high margin error.

Main body

One solution to this problem is to use DNA methylation methods. DNA methylation markers for tissue identification at age-associated CpG sites have been suggested as the most informative biomarkers for estimating the age of an unknown donor. This review aims to give an overview of DNA methylation profiling for estimating the age in cases of forensic relevance and the important aspects in determining the mean absolute deviation (MAD) or mean absolute error (MAE) of the estimated age. Online database searching was performed through PubMed, Scopus, and Google Scholar with keywords selected for forensic age estimation. Thirty-two studies were included in the review, with variable DNA samples but blood commonly as a source. Pyrosequencing and EpiTYPER were methods mostly used in DNA analysis. The MAD in the estimates from DNA methylation was about 3 to 5 years, which was better than other methods such as those based on telomere length or signal-joint T-cell receptor excision circles. The ELOVL2 gene was a commonly used DNA methylation marker in age estimation.

Conclusion

DNA methylation is a favorable candidate for estimating the age at the time of death in forensic profiling, with an uncertainty mean absolute deviation of about 3 to 5 years in the predicted age. The sample type, platform techniques used, and methods to construct age predictive models were important in determining the accuracy in mean absolute deviation or mean absolute error. The DNA methylation outcome suggests good potential to support conventional STR profiling in forensic cases.

Forensic validation of a panel of 12 SNPs for identification of Mongolian wolf and dog

Wolf (Canis lupus) is a species included in appendices of CITES and is often encountered in cases of alleged poaching and trafficking of their products. When such crimes are suspected, those involved may attempt to evade legal action by claiming that the animals involved are domestic dogs (C. l. familiaris). To respond effectively to such claims, law enforcement agencies require reliable and robust methods to distinguish wolves from dogs. Reported molecular genetic methods are either unreliable (mitogenome sequence based), or operationally cumbersome and require much DNA (un-multiplexed microsatellites), or financially expensive (genome wide SNP genotyping). We report on the validation of a panel of 12 ancestral informative single nucleotide polymorphism (SNP) markers for discriminating wolves from dogs. A SNaPshot multiplex genotyping system was developed for the panel, and 97 Mongolian wolves (C. l. chanco) and 108 domestic dogs were used for validation. Results showed this panel had high genotyping success (0.991), reproducibility (1.00) and origin assignment accuracy (0.97 ± 0.05 for dogs and 1.00 ± 0.03 for wolves). Species-specificity testing suggested strong tolerance to DNA contamination across species, except for Canidae. The minimum DNA required for reliable genotyping was 6.25 pg/μl. The method and established gene frequency database are available to support identification of wolves and dogs by law enforcement agencies.

A combination of genome-wide association study screening and SNaPshot for detecting sex-related SNPs and genes in Cynoglossus semilaevis

Chinese tongue sole (Cynoglossus semilaevis) males and females exhibit great differences in growth rate and appearance. The species is heterogametic (ZW/ZZ) and has sex-reversed "pseudomales" that are genetically female and physiologically male. In this study, we identified eight sex-specific single nucleotide polymorphism (SNP) markers for the sex identification of C. semilaevis by using a combination of genome-wide association study (GWAS) screening and SnaPshot validation. Candidate SNPs were screened using genotyping by sequencing to perform GWAS of the differential SNPs between the sexes of C. semilaevis. The SNP loci were amplified using a multiplex PCR system and detected via SNaPshot, which enables multiplexing of up to 30-40 SNPs in a single assay and ensures high accuracy of the results. The molecular markers detected in our study were used to successfully identify normal males and pseudomales from 45 caught and 40 cultured C. semilaevis specimens. Linkage disequilibrium analysis showed that the eight SNP loci were related to each other, with a strong linkage. Moreover, we investigated the expression of prdm6 mRNA containing a missense SNP and confirmed that the gene is differentially expressed in the gonads of the different sexes of C. semilaevis; the expression of prdm6 mRNA was significantly higher in the males than in the females and pseudomales. This means prdm6 may be related to sex differentiation in C. semilaevis.

Practical applications of DNA genotyping in diagnostic pathology

INTRODUCTION

Among various human tissue identity testing platforms, short tandem repeat (STR) genotyping has emerged as the most powerful and cost-effective method. Beyond forensic applications, tissue identity testing has become increasingly important in modern medical practice, in areas such as diagnostic pathology. Areas covered: A brief overview of various molecular/genetic techniques for identity testing is provided. This includes restriction fragment length polymorphism, single nucleotide polymorphism array and STR genotyping by multiplex PCR. Diagnostic applications of STR genotyping are covered in greater details: genotyping diagnosis of gestational trophoblastic disease, resolving tissue specimen mislabeling or histologic contaminant or 'floaters', bone marrow engraftment/chimerism analysis and interrogation of the primary source of malignancy in patients receiving organ donation. Four clinical cases are then presented to further illustrate these important clinical applications along with discussion of the interpretation, limitations, and pitfalls of STR genotyping. Expert commentary: STR genotyping is currently the most applicable method of identity testing and has extended its role well into the practice of diagnostic pathology with novel and powerful applications beyond forensics.