Possible Genetic Link: Insomnia and Depression

This is one of those "interesting, wonder if it'll ever pan out"
studies.  So far it has been presented at a meeting, but not
published.   The study was summarized in an article on
Medpage Today (free registration):

href="http://www.medpagetoday.com/MeetingCoverage/APSS/14689#ayk">APSS:
Depression and Insomnia May Be Genetically Linked

SEATTLE, June 12 -- Insomnia and mood disorders may share a
common genetic pathway, which could explain both depression and
wakefulness observed in teens, researchers here said.



In a study of more than 1,400 twin pairs, about a third of those who
were diagnosed with depression or anxiety also had insomnia, said
Philip Gehrman, M.D., assistant professor of psychiatry at University
of Pennsylvania School of Medicine, Philadelphia, who presented his
findings at the annual meeting of the Association of Professional Sleep
Societies...



... The twins studied were aged eight to 17, and 749 of the pairs were
monozygotic twin pairs...



...Dr. Gehrman and colleagues studied 1,442 twin pairs and determined
that 1.3% of the sample had depression, while 18% were diagnosed with
anxiety.



Among those with either depression or anxiety, 32.4% had insomnia
compared with 16.5% of adolescents who had insomnia but were free of
clinical anxiety and/or depression...

A few comments.  They studied adolescents.  This is
interesting, but it introduces a confounding variable.  Those who
experience onset of affective or anxiety symptoms in adolescence may
not be representative of the population of persons who develop such
symptoms at any point in their lifetimes.  The same may be true of
insomnia. 



Another thing: it often is not difficult to find an apparent
association between two fairly common conditions.  Figuring out
what, if anything, it means can be devilishly difficult.  It could
simply represent the uninteresting fact that once one thing goes wrong,
it is more likely that something else will go wrong.



Or it could be true that insomnia presents a more specific risk factor
that makes it more likely that a variable genetic vulnerability will be
expressed to an extent that it becomes pathological.  That
hypothesis is attractive, in that it has face validity. 



I sometimes think of depression as an illness involving faulty
regulation of vegetative functions.  That is, some with depression
eat too much, others eat too little; some sleep too much, others too
little; some have low energy, while others are restless.  Some are
exquisitely sensitive to rejection, whereas others are rather
indifferent.  (Rejection sensitivity is not a vegetative symptom,
but the same principle applies.)  It would be interesting to know
if the Gehrman study data would permit association between insomnia and
individual symptoms of depression.  Is insomnia associated with
one particular subtype of depression? 

...Dr. Gehrman said he planned additional studies to
investigate the loci of genes related to insomnia and to identify
relevant mutations that make a young patient more likely to have
insomnia...

This would be a natural follow-up study. It may tell us whether or not
there is anything substantive to the association they found in the
pilot study.  I hope that he also follows these patients over a
longer period of time, to see how well these findings hold up across
the lifespan.