Fetal alcohol spectrum disorders (FASD) is an umbrella term that describes a range of
symptoms associated with prenatal alcohol exposure. Fetal Alcohol Syndrome (FAS) is the
most severe disorder in the spectrum and is a major health problem in South Africa, with a
prevalence rate of 68.0-89.2 per 1000 children of school-going age. The primary cause of
FAS is in utero alcohol exposure. However, secondary factors that contribute to the
syndrome include various genetic, epigenetic and additional environmental factors. The
proposal that paternal preconception alcohol exposure has adverse effects on offspring
development is supported by children born with FASD-like characteristics whose mothers did
not drink but whose fathers were alcoholics. Mouse models further support these findings.
One of the main epigenetic factors that have been shown to be affected by alcohol is DNA
methylation. This chemical modification of DNA is associated with developmentally important
genes known as imprinted genes. Imprinted genes are expressed in a parent of origin
specific manner. Methylation occurs at specific regions in these genes known as
differentially methylated regions (DMRs) or imprinting control regions (ICRs). Alcohol’s ability
to alter DNA methylation at imprinted genes raises the possibility that epigenetic disruption
could contribute to the clinical features seen in FASD.
The main aim of this research was to examine global DNA methylation and locus specific
H19 ICR DNA methylation in spermatozoa, related to alcohol exposure. This was done using
the luminometric methylation assay (LUMA) and bisulfite based quantitative pyrosequencing,
respectively. In this study there was no significant correlation between alcohol exposure and
global DNA methylation (p = 0.17), nor was there a significant correlation with drinking
frequency (p = 0.31). Although not significant, a slight trend towards decreased global DNA
methylation in alcohol-exposed spermatozoa was observed. This suggests that either
alcohol does not affect global sperm DNA methylation or that the technique used in this study was not sensitive enough to detect minor changes in global DNA methylation
percentage.
There was also no significant correlation between alcohol exposure and average H19 ICR
DNA methylation (p = 0.051), nor was there a significant correlation with drinking frequency
(p = 0.47). There was no significant correlation between alcohol exposure and DNA
methylation at individual CpG sites except for CpG 3, where there was a significant increase
in DNA methylation in the drinking group (p = 0.03).
The findings of this study together with the findings of significant selective demethylation at
individual CpG sites within the IG-DMR from another study on the same sperm samples,
suggest that alcohol may have the ability to affect DNA methylation levels in spermatozoa at
certain loci within the sperm genome. However, these loci-specific effects are not reflected in
global DNA methylation levels. These findings do not disprove the hypothesis that there is
an epigenetic mechanism responsible for the paternal effects seen in FASD. Instead they
suggest that the techniques used in this study were not sensitive enough to detect these
changes in DNA methylation or alternatively, alcohol may be exerting its effects through
other epigenetic mechanisms.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/12679 |
| Date | 24 April 2013 |
| Creators | Patel, Sanam |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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