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ABOUT AUTISM SPECTRUM DISORDER (ASD)

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder, present in childhood, involving distinct human deficits or difficulties around social communication and repetitive behaviors. Not every autistic human shares the same difficulties. However, some  of the overlapping difficulties involve:

a)     Social emotional reciprocity i.e. how you share your social world.

b)  Repetitive behaviors of interest and routines, as well as repetitive motor behaviors.

c)      An infrequent or inappropriate use of gestures.

d)     Challenges in social interactions and relationships.

Other difficulties involve high sensitivity to sounds, light, touch, smell or taste. As well as a lack of sensory reactions to pain, temperature or sounds. Although, all of these features are diagnostic, individuals under the ASD umbrella often represent a wide range of severity and often co-occurring signs and symptoms that can include anxiety, depression, sleep disturbance, epilepsy, or savant skills e.g.  obsessive preoccupation with, and memorization of music, maps, historical facts, etc.

Until 2019, according to the statistics, ~ 2.7-3.6% of the American population has been found with an autism diagnosis. Unfortunately, the estimate has been rising over time. Although, ASD ranks at the top of the neuropsychiatric disorders with regard to its relative genetic contribution and variety of clinical manifestations, we still don’t have clear diagnostic biomarkers for it. One of the first successful efforts at isolating true ASD risk genes involved the identification of  mutations in Nlg3 and Nlg4 genes. These genes belong to a phylogenetically conserved family of adhesion proteins located in the post-synapsis. Impaired function of Nlg3 and Nlg4 genes is associated with ASD in humans, and impaired social behavior in mice. Nowadays,  there is  enough evidence to support the association of about a dozen copy number variant (CNV)* loci and more than 100 genes involved in ASD, with this list growing.

The fact that ASD involves very different human features, poses a challenge for the interpretation of results coming from evolutionarily distinct experimental models e.g. mice. For this reason, in addition to the progress in gene discovery, there have been huge efforts to encourage what is known as the “convergence neuroscience research approach”, which involve the intersection among molecular-level, cellular level and circuit level functions across multiple ASD risk genes. This approach has revealed among others that:

1) Developing excitatory neurons in the human cortex differ substantially between ASD and control subjects. In ASD subjects the excitatory neurons in the developing frontal & parietal cortices contain high expression of ASD genes during early mid-gestation.

2) ASD genetic risk may cause disruptions in the neurogenesis of the cortex by disrupting the connectivity of the network within the cortical layers.

3) ASD risk genes are differentially enriched in distinct cell types of the human brain. For example, post-mortem ASD human cortex reveals an increase in the representation of excitatory neurons and microglia in comparison to control brains.

In the last few years,  there has been a global phenomenon of increasing autism prevalence. It is not clear  what is changing in the developing brains to make autism more common. Early diagnosis contributes to improving the cognitive skills of the ASD population. Thus, there has been tremendous efforts to generate  biomarkers that allow for a quick and accurate diagnosis. Some of these efforts involves deep learning algorithms trained to detect  particularities at the level of  behavior e.g.  eye movements &  facial gestures, brain imaging & circuits, as well as genetic profiles. Other strategies involve novel gene therapies like gene replacement, editing, and antisense sense oligonucleotide strategies.

Early diagnosis in combination with cognitive and behavioral therapies are fundamental for improving the cognitive skills and life quality of the ASD population. More work needs to be done in order to guarantee access to early diagnosis regardless of race, gender or social status. It turns out to be fundamental to reflect about how  the ASD population perceive the world, what their needs are  and how we can adapt our environment and social construction for them.

*Copy number variation (CNV) is a phenomenon in which sections of the genome are repeated and the number of repeats in the genome varies between individuals.

Sources:

1) Willsey H.R. et.al (2022), Genomics convergent neuroscience and progress in understanding autism spectrum disorder, Nature Reviews Neuroscience, 323-341.

2) Autism by the numbers (2021), Spectrum’s Guide to Prevalence Estimates, Spectrum, Simons Foundation.

3)https://autismwales.org/en/community-services/i-work-with-children-in-health-social-care/the-birthday-party/

4)     Embracing Autism, A little help for Our Friends Podcast

5)     https://www.spectrumnews.org/

6)    Corthals, et. al., (2017) Neuroligins Nlg2 and Nlg4 affect social behavior in Drosophila Melanogaster, Frontiers in Psychiatry, 1-13.

AUTUMN LEAVES

Fall is probably my favorite season. The autumn light is particularly beautiful and the display of leaves switching from green to yellow, orange, red, or eventually brown makes me think of the beauty of the seasons and changes.

The change in the color of the leaves and their falling is mainly dictated by the calendar.  As the nights grow longer and cooler, a series of biochemical processes in the leaf start to paint the hues of fall. When the trees sense from the environment the cold and shortness of the days, they signal a cascade of biochemical events to start their downbeat for the winter. These signals start to degrade the chlorophyll , the green pigment , that allows the trees to absorb energy from light,  and also makes them green.  Once the chlorophyll starts to degrade, other pigments that have always been in the leaf start to display,  and that is how you get yellows, oranges and sometimes browns. Thus,  autumn colors are given by other non- chlorophyll pigments. The pigments responsible for the autumn palette are:

• carotenoids: producing yellow, orange and brown leaves. These pigments give color to the leaves of birches, poplar and elms, as well as to foods like bananas and carrots.

• anthocyanins: producing red, purples and blended combinations of these. Unlike the carotenoids, the anthocyanins aren’t present throughout the growing season, they are produced once the cold temperatures start. Their formation depends on the breakdown of sugars in the presence of light as the phosphate levels in the leaf start to decrease. These new anthocyanin pigments make leaves turn red or purple. The more sugar the brighter the color. Red & sugar maple trees and foods such as beets and radishes get their colors from this pigment

But,  why would the trees spend energy producing reds for leaves that will fall into the ground? Some scientists think these pigments act as a sunscreen or a deterrent for insects, protecting the leaves as the tree is trying to save as much of the material as possible . In some way the red helps the leaves to hang a bit longer from the tree. Thus, it is a tradeoff,  the tree is using some energy to get the other energy that is present in the leaf back to the tree.  However, this is not a conclusive explanation behind the red pigmentation.

After the leaves change color they are ready to separate from the tree and a little bit of  wind or rain will make them fall to the ground. So before all leaves fall into the ground and the winter arrives, go out for a hike and smile at the autumn and its colors.  

Sources:

1) https://www.compoundchem.com/2014/09/11/autumnleaves/

2) https://www.fs.usda.gov/visit/fall-colors/science-of-fall-colors