Mosaic loss of chromosome Y : methods for detection and consequences for affected leukocytes and men

Abstract: It has been known for centuries that men live shorter lives than women, but until recently, the biological mechanisms driving this sex bias has been poorly understood. Mosaic loss of chromosome Y (mLOY) refers to chromosome Y aneuploidy, a male specific and the most common somatic mutation in human blood cells. Known risk factors include age, smoking and genetic predisposition. Men with mLOY carry a fraction of blood cells without the Y chromosome, due to its loss from hematopoietic progenitor cells during life. Hence, in a single cell LOY is a binary event causing the absence of almost 2% of the male haploid nuclear genome. When measured in bulk samples, it is present as a continuous mosaicism affecting a fraction of cells. A paper published in 1963 demonstrated that mLOY is frequent in cells of the hematopoietic system in aging men, but it was long viewed as a neutral event. In contrast, recent discoveries demonstrate that mLOY in blood is associated with various forms of cancer, autoimmune conditions, Alzheimer’s disease, cardiovascular events, diabetes as well as age-related macular degeneration. Studies support the hypothesis that mLOY in leukocytes may exacerbate disease processes in other organs. Thus, given the associations with several common diseases, mLOY in blood cells could help explain reduced male longevity.A main aim and a long term goal of the work presented in this thesis is the development of novel methods for improved mLOY detection. Focus here is exploration of analytes such as DNA, RNA and proteins, including studies of bulk samples as well as single cell approaches. Among the evaluated methods are SNP-arrays, ddPCR, WGS, RNA-seq and CITE-seq. Furthermore, a novel method called SPARC was developed for co-detection of the transcriptome and a panel of 92 proteins in single cells. Future methods with clinical utility for mLOY should, in addition to robust detection, be able to simultaneously discriminate mLOY in different types of immune cells. The latter builds on recent results showing cell type specificity with regard to disease associations. To meet these needs, single cell analyses using mLOY associated cell surface proteins have been pursued and proof-of-concept established. Implementation of mLOY screening in general populations has the potential to identify men with increased risk for various disease. It could be envisioned that further medical examination of men affected with mLOY would enable earlier diagnoses of ongoing disease processes as well as serving to guide targeted interventions.

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