Genetic and evolutionary studies on imprinted genes and human behavior with special reference to Prader-Willi Syndrome

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(Thesis) Ph.D.
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Genomic imprinting may have evolved due to an evolutionary conflict between alleles of different parental origin, carried by the mother and her offspring, which may be differently related to one's kin. Thus, genomic imprinting may be expected to highlight genes affecting regulatory mechanisms of behavior that may alter the distribution of maternal resources among offspring. The altered behavioral phenotypes shown in neurodevelopmental disorders that involve a lack of expression for one or several imprinted genes, may be further interpreted to represent extreme and dysfunctional phenotypes of human behavior. I have applied the kinship model for evolution of genomic imprinting to relevant literature on neurodevelopmental syndromes of genomic imprinting to address two questions central to understanding how genes interact with neural systems and regulate human behavior. Firstly, I propose how the evolution of genomic imprinting may be reflected in the behavioral phenotypes of the Prader-Willi- and Angelman syndromes (PWS and AS). Secondly, I ask if genetic variation of imprinted genes circulating in typical human populations might also affect non-clinical variation in human behaviors that may be partially co-regulated by imprinted genes. In chapter 2, I show that genetic variation for the maternally expressed UBE3A which is affected in both AS and PWS may also affect non-clinical variation in phenotypes of schizotypy among typically developing individuals. In chapter 3, I review evidence from relevant literature and evaluate whether phenotypes of sleep and eating in PWS and AS may be partly opposite to one another and propose hypotheses on how evolution of genomic imprinting may be reflected in the neural and behavioral phenotypes of AS and PWS. In chapter 4, I show that genetic variation of the paternally expressed SNORD116 gene, which shows a lack of expression in PWS, may also affect non-clinical variation in schizotypy among typically developing females. Finally, in chapter 5, I show that non-clinical variation in phenotypes of depression, schizotypy, autism spectrum cognition, social anxiety, sleep problems and emotional eating show significant co-variation in a population of typical individuals. The pattern of co-variation shown may reflect influences of genetic regulatory mechanisms involved in hypothalamic neural pathways, which have been shown to jointly alter the phenotypes of sleep, feeding and behavior. Behavioral phenotypes which are co-regulated by hypothalamic pathways may also be affected by variation of imprinted genes as several paternally expressed imprinted genes have also been shown to exert effects on hypothalamic pathways. In summary, I show that paternally and maternally expressed imprinted genes may exert partly opposite effects on human behaviors that may alter phenotypes affecting the distribution of maternal resources among offspring. These behavioral alterations may further reveal genetic and neural mechanisms affecting human behaviors and may thus hold further implications for mental health and well-being both in clinical settings and among healthy individuals.
162 pages.
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Thesis advisor: Crespi, Bernard
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