Learning problems

Link between handedness and dyslexia

January, 2011

A genome study has found a gene variant that leads to greater right-hand skill in dyslexics, but not others. The gene is implicated in embryonic development.

While brain laterality exists widely among animal species, the strong dominance of right-handedness in humans is something of an anomaly. As this implies a left-hemisphere dominance for motor function, it’s been suggested that the evolution of language (also mainly a function of the left hemisphere) may be behind the right-handed bias, leading to a search for a connection between hand preference and language disorders. To date, no convincing evidence has been found.

However, a genetic study of 192 dyslexic children has now revealed a strong link between a variant of a gene called PCSK6 and relative hand skill in these children. Specifically, those who carried the variant in PCSK6 were, on average, more skilled with their right hand compared to the left than those not carrying the variant. However, among the general population, this gene variant is associated with less right-hand skill.

The findings provide evidence for a link between brain lateralization and dyslexia. The gene’s protein is known to interact with another protein (NODAL) that plays a key role in establishing left-right asymmetry early in embryonic development, suggesting that the gene may affect the initial left-right patterning of the embryo, with consequences for cerebral lateralization.

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Children with autism have distinctive patterns of brain activity

December, 2010

An imaging study has found three different brain signatures discriminating children with autistic spectrum disorders, siblings of children with ASD, and other typically-developing children.

Last month I reported on a finding that toddlers with autism spectrum disorder showed a strong preference for looking at moving shapes rather than active people. This lower interest in people is supported by a new imaging study involving 62 children aged 4-17, of whom 25 were diagnosed with autistic spectrum disorder and 20 were siblings of children with ASD.

In the study, participants were shown point-light displays (videos created by placing lights on the major joints of a person and filming them moving in the dark). Those with ASD showed reduced activity in specific regions (right amygdala, ventromedial prefrontal cortex, right posterior superior temporal sulcus, left ventrolateral prefrontal cortex, and the fusiform gyri) when they were watching a point-light display of biological motion compared with a display of moving dots. These same regions have also been implicated in previous research with adults with ASD.

Moreover, the severity of social deficits correlated with degrees of activity in the right pSTS specifically. More surprisingly, other brain regions (left dorsolateral prefrontal cortex, right inferior temporal gyrus, and a different part of the fusiform gyri) showed reduced activity in both the siblings group and the ASD group compared to controls. The sibling group also showed signs of compensatory activity, with some regions (right posterior temporal sulcus and a different part of the ventromedial prefrontal cortex) working harder than normal.

The implications of this will be somewhat controversial, and more research will be needed to verify these findings.

Reference: 

[1987] Kaiser, M. D., Hudac C. M., Shultz S., Lee S. M., Cheung C., Berken A. M., et al.
(2010).  Neural signatures of autism.
Proceedings of the National Academy of Sciences.

Full text available at http://www.pnas.org/content/early/2010/11/05/1010412107.full.pdf+html

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Autism study reveals how a genetic variant rewires the brain

December, 2010

An imaging study has revealed how one of the many genes implicated in autism is associated with an atypical pattern of connectivity between the hemispheres and within and from the frontal lobe.

Many genes have been implicated in autism; one of them is the CNTNAP2 gene. This gene (which is also implicated in specific language disorder) is most active during brain development in the frontal lobe. An imaging study involving 32 children, half of whom had autism, has revealed that regardless of their diagnosis, the children carrying the risk variant showed communication problems within and with the frontal lobe. The frontal lobe was over-connected to itself and poorly connected to the rest of the brain, particularly the back of the brain.

There were also differences in connectivity between the left and right sides of the brain — in those with the non-risk gene, communication pathways in the frontal lobe linked more strongly to the left side of the brain (which is more strongly involved in language), but in those with the risk variant, the communications pathways connected more broadly to both sides of the brain.

The findings could lead to earlier detection of autism, and new interventions to strengthen connections between the frontal lobe and left side of the brain. But it should be emphasized that the autistic spectrum disorders probably encompass a number of different genetic patterns associated with different variants of ASD.

It should also be emphasized that this gene variant, although it increases the risk of various neurodevelopmental disorders (such as specific language impairment, which has also been associated with this gene), is found among a third of the population. So the pattern of connectivity, although not ‘normal’ (i.e., the majority position), is not abnormal. It would be interesting to explore whether other, more subtle, cognitive differences correlate with this genetic difference.

Reference: 

Scott-Van Zeeland., A.A. et al. 2010. Altered Functional Connectivity in Frontal Lobe Circuits Is Associated with Variation in the Autism Risk Gene CNTNAP2. Science Translational Medicine, 2 (56), DOI: 10.1126/scitranslmed.3001344 http://stm.sciencemag.org/content/2/56/56ra80.abstract

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Girls less likely to be diagnosed autistic even when symptoms severe

December, 2010

A new study finds that gender and maternal assertiveness are factors in determining whether children with autistic symptoms are diagnosed with ASD.

No one is denying that boys are far more likely to be autistic than girls, but a new study has found that this perception of autism as a male disorder also means that girls are less likely to be diagnosed with autistic spectrum disorder (ASD) even when their symptoms are equally severe.

Another factor affecting diagnosis was maternal age — those diagnosed with ASD were likely to have older mothers. It’s suggested that this may be because older mothers are better at identifying their children's difficulties and have more confidence in bringing concerns to the clinic. This is supported by the finding that first-born children were less likely to be diagnosed with ASD, as were children of mothers with depression.

Ethnic origin, maternal class and mother's marital status did not significantly predict a child either having an ASD diagnosis or displaying severe autistic traits.

The findings were based on an analysis of data from a longitudinal UK cohort study, the Avon Longitudinal Study of Parents and Children (ALSPAC).

Reference: 

Russell, G., Steer, C. & Golding, J. 2010. Social and demographic factors that influence the diagnosis of autistic spectrum disorders. Social Psychiatry and Psychiatric Epidemiology. DOI 10.1007/s00127-010-0294-z.
Full text is available at http://springerlink.com/content/a67371l826m1xl76/fulltext.pdf

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Fetal alcohol exposure associated with a decrease in cognitive performance

November, 2010

Fetal exposure to large amounts of alcohol is found to be associated with reduced cognitive efficiency in perception, attention and recognition memory, in older children.

Data from 217 children from Inuit communities in Arctic Quebec (average age 11), of whom some had mothers that reported binge drinking during pregnancy, has revealed that the alcohol-exposed group, while similar to the control in accuracy and reaction time, showed a significant differences in their brains’ electrical activity while doing those tasks (a Go/No-go response inhibition task and a continuous recognition memory task). The differences suggest that fetal alcohol exposure is associated with reduced efficiency in the initial extracting of the meaning of a stimulus, reduced allocation of attention to the task, and poorer conscious recognition memory processing.

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An early marker of autism

October, 2010

A strong preference for looking at moving shapes rather than active people was evident among toddlers with autism spectrum disorder.

A study involving 110 toddlers (aged 14-42 months), of whom 37 were diagnosed with an autism spectrum disorder and 22 with a developmental delay, has compared their behavior when watching a 1-minute movie depicting moving geometric patterns (a standard screen saver) on 1 side of a video monitor and children in high action, such as dancing or doing yoga, on the other.

It was found that only one of the 51 typically-developing toddlers preferred the shapes, but 40% of the ASD toddlers did, as well as 9% of the developmentally delayed toddlers. Moreover, all those who spent over 69% of the time focusing on the moving shapes were those with ASD.

Additionally, those with ASD who preferred the geometric images also showed a particular pattern of saccades (eye movements) when viewing the images — a reduced number of saccades, demonstrated in a fixed stare. It’s suggested that a preference for moving geometric patterns combined with lengthy absorption in such images, might be an early identifier of autism. Such behavior should be taken as a signal to look for other warning signs, such as reduced enjoyment during back-and-forth games like peek-a-boo; an unusual tone of voice; failure to point at or bring objects to show; and failure to respond to their name.

Reference: 

[1891] Pierce, K., Conant D., Hazin R., Stoner R., & Desmond J.
(2010).  Preference for Geometric Patterns Early in Life As a Risk Factor for Autism.
Arch Gen Psychiatry. archgenpsychiatry.2010.113 - archgenpsychiatry.2010.113.

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Sensory integration in autism

October, 2010

A new study provides evidence for the theory that sensory integration is impaired in autism.

Children with autism often focus intently on a single activity or feature of their environment. A study involving 17 autistic children (6-16 years) and 17 controls has compared brain activity as they watched a silent video of their choice while tones and vibrations were presented, separately and simultaneously.

A simple stimulus takes about 20 milliseconds to arrive in the brain. When information from multiple senses registers at the same time, integration takes about 100 to 200 milliseconds in normally developing children. But those with autism took an average of 310 milliseconds to integrate the noise and vibration when they occurred together. The children with autism also showed weaker signal strength, signified by lower amplitude brainwaves.

The findings are consistent with theories that automatic sensory integration is impaired in autism, and may help explain autism’s characteristic sensitivity to excessive sensory stimulation.

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Light shed on the cause of the most common learning disability

September, 2010

The discovery that the mutated NF1 gene inhibits working memory through too much GABA in the prefrontal cortex offers hope for an effective therapy for those with the most common learning disability.

Neurofibromatosis type 1 (NF1) is the most common cause of learning disabilities, caused by a mutation in a gene that makes a protein called neurofibromin. Mouse research has now revealed that these mutations are associated with higher levels of the inhibitory neurotransmitter GABA in the medial prefrontal cortex. Brain imaging in humans with NF1 similarly showed reduced activity in the prefrontal cortex when performing a working memory task, with the levels of activity correlating with task performance. It seems, therefore, that this type of learning disability is a result of too much GABA in the prefrontal cortex inhibiting the activity of working memory. Potentially they could be corrected with a drug that normalizes the excess GABA's effect. The researchers are currently studying the effect of the drug lovastatin on NF1 patients.

Reference: 

[1688] Shilyansky, C., Karlsgodt K. H., Cummings D. M., Sidiropoulou K., Hardt M., James A. S., et al.
(2010).  Neurofibromin regulates corticostriatal inhibitory networks during working memory performance.
Proceedings of the National Academy of Sciences. 107(29), 13141 - 13146.

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New technology can help assess autistic & language disorders

August, 2010

New technology offers hope of early diagnosis of both autism spectrum and language disorders, as well as promising help to parents in assessing the effectiveness of therapy.

A new automated vocal analysis technology can discriminate pre-verbal vocalizations of very young children with autism with 86% accuracy. The LENA™ (Language Environment Analysis) system also differentiated typically developing children and children with autism from children with language delay. The processor fits into the pocket of specially designed children's clothing and records everything the child vocalizes. LENA could not only enable better early diagnosis of autism spectrum disorders, but also allow parents to continue and supplement language enrichment therapy at home and assess their own effectiveness for themselves.

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ADHD linked to welfare benefits, low maternal education, solo parents

July, 2010

Data from an entire birth cohort in Sweden has revealed that poverty and having a poorly educated mother are major risk factors in ADHD (or at least being medicated for it).

A national Swedish study involving the 1.16 million children in a national birth cohort identified nearly 8000 on the country's Prescribed Drug Register as using a prescription for ADHD medication (and thus assumed to suffer from severe ADHD). These children were significantly more likely to come from a family on welfare benefits (135% more likely), to have a mother with only the most basic education (130% more likely than those with mothers with university degrees), and to come from a single parent family (54% more likely). Boys were three times more likely to be on ADHD medication than girls, with medication use highest in boys aged between 10 and 15. The finding that family adversity is such a strong risk factor points to the need for more research into the role of environment

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