The Connectome in the Human Brain: Defining its Heritability and Association with ADHD

Gustavo Sudre:
Attention Deficit and Hyperactivity Disorder, or ADHD, is the most common neuropsychiatric
disorder of childhood. About one in 1- kids here in Montgomery County are diagnosed with
a disorder, and one in 15 takes psychostimulants as a treatment. Now, what many people don’t
know is that about 30 percent of those kids are still going to have ADHD as adults, and
those adults usually suffer of lower educational and working achievements. Now, one of the
issues is that ADHD is currently diagnosed using a clinical interview. In our lab, we
aim to quantify ADHD using genetics and neural data, and this way have a better understanding
of the disorder. But what kind of markers are we looking for? Well, we know that ADHD
is highly heritable; we also know that ADHD evolves different systems in the brain. So
here we ask, what connections in the brain are both heritable and associated with symptoms
of ADHD? The brain imaging that we’re going to be
using is called diffusion tractography imaging, or DTI. DTI uses properties of water diffusion
to infer the orientation of different connections in the brain. These connections are called
white fiber tracts. So think of a brain image as different 3D cubes, and within each of
these cubes, we’re going to estimate their orientation — and that’s the different
colors in the figure — of the different connections. Then, based on this orientation, we’re going
to group the different fiber tracks into 11 major tracks. That’s what we show here in
the lateral view of the brain. For each of these 11 major tracks, we’re going to estimate
two properties. So think of these connections as a water hose.
Water in a hose can flow along the axis of the hose — so that would be the axial diffusivity
— or along the radius of the hose; that will be the radial diffusivity. So for each of
these 11 major tracks, we have these two different properties. Now, in our findings, out of the
22 possible variables, 10 are highly heritable in ADHD. Out of these 10, four are also associated
with symptoms of ADHD. And I show these tracks in the rotating brain. The fascinating thing
is that these tracks connect regions that have been shown in the literature to be associated
with ADHD. Also, another very important finding is that these results are restricted to the
radial component. Now, people have shown in the literature that the radial component is
related to myelin. Myelin is an insulating sheet in these connections, and it’s crucial
for proper functioning of the nervous system. So we see that these different properties,
the RD properties could be a target for future genomic studies. [end of transcript]

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