• Human Twins at Birth Highlight Importance of Intrauterine Environment

ScienceDaily (July 15, 2012) — Your genes determine much about you, but
environment can have a strong influence on your genes even before birth, with
consequences that can last a lifetime. In a study published online in Genome
Research, researchers have for the first time shown that the environment
experienced in the womb defines the newborn epigenetic profile, the chemical
modifications to DNA we are born with, that could have implications for disease
risk later in life.

Epigenetic tagging of genes by a chemical modification called DNA methylation is
known to affect gene activity, playing a role in normal development, aging, and
also in diseases such as diabetes, heart disease, and cancer. Studies conducted
in animals have shown that the environment shapes the epigenetic profile across
the genome, called the epigenome, particularly in the womb. An understanding of
how the intrauterine environment molds the human epigenome could provide
critical information about disease risk to help manage health throughout life.

Twin pairs, both monozygotic (identical) and dizygotic (fraternal), are ideal
for epigenetic study because they share the same mother but have their own
umbilical cord and amniotic sac, and in the case of identical twins, also share
the same genetic make-up. Previous studies have shown that methylation can vary
significantly at a single gene across multiple tissues of identical twins, but
it is important to know what the DNA methylation landscape looks like across the
genome.

In this report, an international team of researchers has for the first time
analyzed genome-scale DNA methylation profiles of umbilical cord tissue, cord
blood, and placenta of newborn identical and fraternal twin pairs to estimate
how genes, the shared environment that their mother provides and the potentially
different intrauterine environments experienced by each twin contribute to the
epigenome. The group found that even in identical twins, there are widespread
differences in the epigenetic profile of twins at birth.

"This must be due to events that happened to one twin and not the other," said
Dr. Jeffrey Craig of the Murdoch Childrens Research Institute (MCRI) in
Australia and a senior author of the report. Craig added that although twins
share a womb, the influence of specific tissues like the placenta and umbilical
cord can be different for each fetus, and likely affects the epigenetic profile.

Interestingly, the team found that methylated genes closely associated with
birth weight in their cohort are genes known to play roles in growth,
metabolism, and cardiovascular disease, lending further support to a known link
between low birth weight and risk for diseases such as diabetes and heart
disease. The authors explained that their findings suggest the unique
environmental experiences in the womb may have a more profound effect on
epigenetic factors that influence health throughout life than previously thought.

Furthermore, an understanding of the epigenetic profile at birth could be a
particularly powerful tool for managing future health. "This has potential to
identify and track disease risk early in life, said Dr. Richard Saffery of the
MCRI and a co-senior author of the study, "or even to modify risk through
specific environmental or dietary interventions."

Journal Reference:

Gordon L, Joo JE, Powell JE, Ollikainen M, Novakovic B, Li X, Andronikos R,
Cruickshank MN, Conneely KN, Smith AK, Alisch RS, Morley R, Visscher PM, Craig
JM, Saffery R. Neonatal DNA methylation profile in human twins is specified by a
complex interplay between intrauterine environmental and genetic factors,
subject to tissue-specific influence. Genome Res, July 16, 2012 DOI:
10.1101/gr.136598.111

Cold Spring Harbor Laboratory (2012, July 15). Differences between human twins
at birth highlight importance of intrauterine environment. ScienceDaily.
Retrieved July 17, 2012, from
http://www.sciencedaily.com­ /releases/2012/07/120715193843.htm