Improving the age estimation model for toenails.

In a previous study, we have provided the first proof that chronological age can be estimated through DNA methylation (DNAm) patterns in fingernails and toenails. DNAm data of 15 CpGs located in 4 genetic markers (ASPA, EDARADD, ELOVL2 and PDE4C) were evaluated, of which variable selection yielded age prediction models with a mean absolute deviation (MAD) ranging from 7.68 to 9.36 years, depending on the sampling location. Three additional age-associated markers (KLF14, MIR29B2CHG and TRIM59) were assessed in the current study with the goal of increasing the prediction accuracy of the model initially constructed for toenails. This new and improved age estimation assay yielded an MAD of 4.82 and 5.61 years for the training and test set, respectively. The feasibility of the application for post-mortem cases was also demonstrated through testing a limited set of samples collected from deceased individuals.

Age determination through DNA methylation patterns in fingernails and toenails.

Over the past decade, age prediction based on DNA methylation has become a vastly investigated topic; many age prediction models have been developed based on different DNAm markers and using various tissues. However, the potential of using nails to this end has not yet been explored. Their inherent resistance to decay and ease of sampling would offer an advantage in cases where post-mortem degradation poses challenges concerning sample collection and DNA-extraction. In the current study, clippings from both fingernails and toenails were collected from 108 living test subjects (age range: 0-96 years). The methylation status of 15 CpGs located in 4 previously established age-related markers (ASPA, EDARADD, PDE4C, ELOVL2) was investigated through pyrosequencing of bisulphite converted DNA. Significant dissimilarities in methylation levels were observed between all four limbs, hence both limb-specific age prediction models and prediction models combining multiple sampling locations were developed. When applied to their respective test sets, these models yielded a mean absolute deviation between predicted and chronological age ranging from 5.48 to 9.36 years when using ordinary least squares regression. In addition, the assay was tested on methylation data derived from 5 nail samples collected from deceased individuals, demonstrating its feasibility for application in post-mortem cases. In conclusion, this study provides the first proof that chronological age can be assessed through DNA methylation patterns in nails.