Pediatr Res. 2015 (Jun); 77 (6): 823–828
Pärtty A, Kalliomäki M, Wacklin P, Salminen S, Isolauri E
Department of Pediatrics,
University of Turku and Turku University Hospital,
Finnish Red Cross Blood Service,
Functional Foods Forum,
University of Turku,
BACKGROUND: Recent experimental evidence suggests that gut microbiota may alter function within the nervous system providing new insight on the mechanism of neuropsychiatric disorders.
METHODS: Seventy-five infants who were randomized to receive Lactobacillus rhamnosus GG (ATCC 53103) or placebo during the first 6 mo of life were followed-up for 13 y. Gut microbiota was assessed at the age of 3 wk, 3, 6, 12, 18, 24 mo, and 13 y using fluorescein in situ hybridization (FISH) and qPCR, and indirectly by determining the blood group secretor type at the age of 13 y. The diagnoses of attention deficit hyperactivity disorder (ADHD) and Asperger syndrome (AS) by a child neurologist or psychiatrist were based on ICD-10 diagnostic criteria.
RESULTS: At the age of 13 y, ADHD or AS was diagnosed in 6/35 (17.1%) children in the placebo and none in the probiotic group (P = 0.008). The mean (SD) numbers of Bifidobacterium species bacteria in feces during the first 6 mo of life was lower in affected children 8.26 (1.24) log cells/g than in healthy children 9.12 (0.64) log cells/g; P = 0.03.
CONCLUSION: Probiotic supplementation early in life may reduce the risk of neuropsychiatric disorder development later in childhood possible by mechanisms not limited to gut microbiota composition.
From the FULL TEXT Article:
Psychiatric disorders are already ranked among the leading
causes of disability in industrialized countries. With
the current progressive increase in the incidence, they may
be expected to assume the first place also globally within
the next few years. [1, 2] Attention-deficit hyperactivity disorder
(ADHD), characterized by inattention, impulsivity,
and hyperactivity, affects three to seven percent of children
worldwide. [3, 4] Moreover, symptoms of inattention and
hyperactivity are frequent in children with Asperger syndrome
(AS), which is characterized by stereotyped behavior
and deficient social interaction and communication skills. 
Besides the common behavioral features, shared biological
pathways and neuroanatomical links between these diseases
have been reported. [5, 6]
Despite intensive research on ADHD and AS, the precise
chain of pathological events underlying them remains
unknown. The available data indicate ADHD and AS to be
multifactorial disorders, in which genetic risk predominates,
reinforced by various environmental and biological factors
such as fetal stress, prematurity, toxins, and diet.  Recently,
the search for etiologies has been expanded both within the
central nervous system and beyond. Experimental data are
accumulating to suggest that the presence of gut microbiota
as such, as compared with the absence of it, and especially its
certain beneficial bacteria, probiotics, make for altered function
within the nervous system. [8–12] As a recent empirical
study indicates  probiotics may provide a tool to manipulate
brain activity even in humans.
To test the hypothetical involvement of the gut brain-axis
in the manifestation of ADHD and AS, we analyzed the association
of compositional development of the gut microbiota,
the blood group secretor type as an indirect evidence of gut
microbiota involvement, and the impact of specific probiotic
intervention on the emergence of these two neuropsychiatric
disorders in a cohort followed until 13 y of age.
The results of our preliminary study demonstrate for the first
time that specific probiotics may reduce the risk of the development
of ADHD and AS possibly by mechanisms not directly
associated with gut microbiota composition, since no single constant
microbiota composition or their difference could be distinctive
in children with or without neuropsychiatric disorders.
These findings must be viewed in the light of some caution as
preliminary and initial observation into this novel area. First,
our probiotic intervention study was originally designed and
statistically powered for prevention of atopic eczema, not for
prevention of more uncommon neuropsychiatric disorders
ADHD and AS. Regardless of that, it is interesting to notice
that allergic disease has been shown to be associated with an
increased risk of ADHD and differences in neurodevelopment [14, 15] suggesting a possibility for common environmental
determinants. Second, the number of drop-outs was quite considerable
during the follow-up. Therefore, we cannot discount
the possibility that the issue would not have biased our findings.
However the number of drop-outs was equally divided
in the both intervention groups and base-line characteristics
of the drop-outs and the study finishers were similar, except
for the duration of exclusive breast-feeding, demonstrating
that these two groups were unbiased in almost all of the
known factors. On the other hand, the careful and prospective
13–y follow-up period is the strength of the study. A further
strength of the study is that gut microbiota has been analyzed
comprehensively by FISH and qPCR as well as indirectly by
blood group secretor type analysis.
ADHD is a disease of substantial genetic predisposition, as
suggested by a number of adoption, twins, and family studies. [7, 16, 17] This notwithstanding, recent studies document
up to 20% discordance in identical twins, leaving room for
environmental and epigenetic determinants of ADHD. Thus
far, prenatal exposure to maternal smoking , low birth
weight, prematurity [19, 20], and specific environmental exposures
such as lead and organic pollutants  have been linked
to ADHD. In contrast, research on dietary factors such as
sugar, artificial food colorings, zinc, iron, and ω–3 fatty acids,
has established only vague causality in ADHD , despite
some hints of their therapeutic potential. [21, 22] An empirical
elimination diet has indeed been shown to be effective in
the treatment of ADHD.  Moreover, breastfeeding, as a
potent inducer of Bifidobacteria in the gut microbiota ,
has proved to be associated with lower levels of conduct disorder
symptoms in middle childhood, which is in line with our
findings in this study  demonstrating defiencies in early
Bifidobacterium composition in those with later ADHD or AS.
Although the precise possible mechanisms of action of
the gut microbiota in the gut-brain axis are unclear, a previous
experimental study offers an interesting clue. In
the study in question, mice with experimentally induced
chronic colitis showed anxiety-like behavior. Treatment with
Bifidobacterium longum abolished such behavior. However,
the anxiolytic effect of Bifidobacterium longum was absent in
vagotomized mice, suggesting that the effect was transmitted
to the central nervous system by activating vagal pathways at
the level of the enteric nervous system.  It is thus intriguing
to note that in our study the amount of the same species
was found to be decreased in early life in children later developing
ADHD or AS.
Our data demonstrate that early administration of
Lactobacillus rhamnosus GG may reduce the risk of ADHD
and AS. Lactobacillus rhamnosus GG has been shown to stabilize
the gut permeability barrier by effects on tight junctions,
mucin production and antigen-specific immunoglobulin
A production.  In addition, a recent experimental study
has demonstrated that Lactobacillus rhamnosus regulates,
again via the vagus nerve, emotional behavior and the central
GABAergic system, which is also associated with neuropsychiatric
disorders. [11, 26] Of note, a recent study with
healthy women demonstrated that a consumption of a mixture
of probiotic bacteria had significant effects on brain regions
that control central processing of emotion and sensation. 
Probiotics had no significant effect on microbiota composition
in the study suggesting that the effects on central nervous
system were either induced by altered vagal afferent signaling
or by systemic metabolic changes related to probiotic intake.  Furthermore, another experimental study with mice
showed that pretreatment with probiotic Lactobacillus rhamnosus
prevents learning and memory dysfunction in Citrobacter
rodentium-infected mice.  It thus remains to be elucidated
whether these effects of Lactobacillus rhamnosus are of
importance in the development of neuropsychiatric disorders
in humans. However, in accord with our clinical findings here
it has been postulated that neural pathways may alter already
early in development. If such an alteration takes place at a critical
moment, the sequential dysfunction of the gut-brain axis
may become relatively constant into adulthood. [28, 29]
Our findings demonstrate a possible preventive risk reducing
effect of a probiotic LGG on later development of ADHD
and AS. We also report an interconnection between the early
gut microbiota and development of these neuropsychiatric disorders,
although no single constant microbiota composition
component or change was detected. However, keeping in mind
the above-mentioned limitations of the study, we consider the
findings preliminary but encouraging for further studies of
the subject both in the area of well-powered clinical trials and
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