Ocular swabs on exhumed bodies: An alternative to the collection of “classical” tissue samples in forensic genetics

The eye in forensic practice: In the dead

Post-mortem examination of the eye provides valuable forensic information yet is often overlooked. This brief review focuses on determining the cause/manner of death and post-mortem interval. External eye findings like corneal haziness and tache noire, combined with post-mortem changes in the iris, lens, retina and vitreous humour, can help estimate time since death. Ocular biometrics (iris/retinal scans) may facilitate identification. Age-related ocular changes can provide insights. The eye offers clues into personality (corneal tattooing, trichotillomania) and cause of death (petechiae in strangulation, retinal haemorrhages in abusive head trauma). Ocular trauma and underlying eye disease may be evident. Toxicology of vitreous humour can detect drugs/poisons. As a window into systemic disease and age-related changes, the eye aids pathology interpretations and, accordingly, post-mortem examinations have value. Ocular findings should not be overlooked in forensic examinations as they provide distinct information in determining cause/manner of death and post-mortem interval.

Differential gene expression of the healthy conjunctiva during the day

PURPOSE

To determine if there is diurnal variation in gene expression in normal healthy conjunctival cells.

METHODS

Bulbar conjunctival swab samples were collected from four healthy subjects in the morning and evening of the same day. The two swab samples were taken from one eye of each participant, with a minimum of five hours gap between the two samples. RNA was extracted and analysed using RNA sequencing (RNA-Seq).

RESULTS

A total of 121 genes were differentially expressed between the morning and the evening conjunctival samples, of which 94 genes were upregulated in the morning, and 27 genes were upregulated in the evening. Many of the genes that were upregulated in the morning were involved in defence, cell turnover and regulation of gene expression, while the genes upregulated in the evening were involved in signalling and mucin production.

CONCLUSIONS

This study has identified several genes whose expression changes over the course of the day. Knowledge of diurnal variations of conjunctival gene expression provides an insight into the regulatory status of the healthy eye and provides a baseline for examining changes during ocular surface disease.

Suitability of specific soft tissue swabs for the forensic identification of highly decomposed bodies

When decomposition of a recovered body is fairly advanced, identification based on common morphologic features is often impossible. In these cases, short tandem repeat (STR) marker genotyping has established itself as a convenient and reliable alternative. However, at very progressed stages of decomposition, postmortem tissue putrefaction processes can decrease DNA yields considerably. Hence, not all types of tissue are equally suitable for successful STR marker-based postmortem identification. Bone or dental material is often analysed in corpses with advanced decompositional changes. However, processing of these materials is very elaborate and time and resource consuming. We have therefore focused on the suitableness of various types of soft tissue swabs, where DNA extraction is easier and faster. By sampling 28 bodies at various stages of decomposition, we evaluated the suitability of different tissues for genotyping at varying degrees of physical decay. This was achieved by a systematic classification of the sampled bodies by morphological scoring and subsequent analysis of multiple tissue swabs of the aortic wall, urinary bladder wall, brain, liver, oral mucosa and skeletal muscle. In summary, we found variable degrees of suitability of different types of soft tissue swabs for DNA-based identification. Swabs of the aortic wall, the urinary bladder wall and brain tissue yielded the best results - in descending order - even at advanced levels of decay.