considerable shared environmental influences on hoarding symp-
toms amongst girls. However, similar findings of sex differences
during adolescence have been reported previously regarding
genetic and environmental influences for OCD, [48,49] weight
, and pubertal development . Furthermore, dynamic
developmental genetic effects from childhood to young adulthood,
expressed in genetic attenuation and innovation (i.e. the decline in
impact of certain genes and the activation of genes which
previously had no effect) in symptoms of anxiety and depression
are well documented . It seems plausible that hoarding may
become progressively more heritable over time as the influence of
shared familial environment decreases when young people leave
their parents’ home and have stronger control over their own
living space. Longitudinal studies of the heritability of hoarding
symptoms in young adulthood and beyond are needed to elucidate
developmental trajectories of hoarding in both sexes.
The results should be interpreted considering several limita-
tions. First, we based our classification of clinically significant
hoarding symptoms on a measure not specifically validated in an
adolescent population. Thus, the possibility that it did not capture
hoarding symptoms equally well as in adults cannot be ruled out.
Hopefully, the modification of the clutter item increased its
relevance for this age group. Second, prevalence estimates should
be seen as indicative rather than definitive because we could not
conclusively rule out other medical or psychiatric conditions that
are known to lead to hoarding behavior [52,53]. Third, although
ADHD, ASD and OCD are relatively stable prevalence-wise in
the age span from 9/12 to 15 years, more precise estimates of their
co-occurrence with hoarding symptoms would have been obtained
had they been assessed at age 15 years and not at age 9/12; hence,
we cannot totally exclude an under- or possibly overestimation of
ADHD, ASD and OCD comorbidity. Fourth, albeit modeled
closely after DSM-IV-TR-criteria , comorbid OCD was not
determined using a validated measure, and was based solely on
parental report. Thus, the OCD comorbidity rate might have been
underestimated by parents and should therefore be interpreted
cautiously. Fifth, and finally, since ASD and ADHD were
significantly more common among non-responders, we cannot
rule out that the true comorbidity of hoarding symptoms and
neurodevelopmental disorders might be higher.
This study is the first to investigate the occurrence of hoarding
symptoms in a large population based sample of adolescents.
Hoarding symptoms were prevalent among adolescents and
usually appeared without co-occurring ADHD, ASD and OCD.
Furthermore, the same etiological factors seemed to influence
hoarding symptoms in both sexes although the genetic effect was
much stronger in boys. Longitudinal studies are required to
elucidate the developmental trajectories of hoarding symptoms
and their heritability from adolescence onto adulthood.
The authors would like to thank Camilla Palm at the Department of
Medical Epidemiology and Biostatistics, Karolinska Institutet for assistance
in data management and preparation.
Conceived and designed the experiments: DMC PL HA ZC CHG SL NL
CR ES. Analyzed the data: VZI DMC PL ZC CR. Wrote the paper: VZI
DMC ES PL HA ZC CHG SL NL CR.
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PLOS ONE | www.plosone.org 6 July 2013 | Volume 8 | Issue 7 | e69140