Friday, July 11, 2014

Understanding Genetics: Chromosome 2

Chromosome 2 is the second largest human chromosome containing approximately 243 million DNA pairs, according to the Genetics Home Reference. It is also one of the "oldest" in human evolution. Chromosome 2 contains approximately 1,300-1,400 of the total genes that provide protein making instructions. Genetic changes to C2 (as I will now call Chromosome 2) have great impact. Several types of cancer have been identified as a result of C2 changes. Myelodysplastic Syndrome, an affliction of the blood and bone marrow, is due to three copies of Chromosome 2 strands, instead of the typical two. Deleting parts of C2 can cause many disorders such as obesity, short stature, and even Autism.

In 2004 Genome News Network reported a research study originally published by the American Journal of Psychiatry. This study included approximately 2,000 people of which 720 were afflicted with Autism. They found an association between Chromosome 2 and Autism. C2 is responsible, in part, for language development. As we know, one of the hallmarks of Autism is a language deficit. The specific gene on Chromosome 2 that impacts this area is called SLC25A12. This gene occurs with greater frequency in individuals with Autism and family members without this disorder. Researchers point out that Autism impacts many different genes, but someone with this specific gene have two times the risk of developing ASD.

In 2007, the Scientific American, published an article from research spanning 19 countries, 120 scientists, 50 institutions and 1,168 families. The report was originally published in Nature Genetics. Using specialized equipment the researchers scanned the DNA looking for variations in DNA that could contribute to ASD. They found significant variations on Neurexin 1 on Chromosome 2 and also a sequencing issue on Chromosome 11 (covered in a different blog).

What is Neurexin 1? This group of genes controls the coding for proteins involved in neuron communication. Also associated with glutamine, the neurotransmitter responsible for elevating neuron activity and brain wiring during early development, Neurexin 1 is believed to be involved in building synapses and some links which send and receive electrical signals. Some subjects of this study were found to have a deletion of the Neurexin 1 gene.

In 2011 very exciting research was unveiled by the American Journal of Human Genetics and reported at the 61st American Society of Human Genetics Annual Meeting. Medscape published an article about this research from Canada. Scientists studied approximately 2,275 subjects and discovered that in every individual affected by microdeletion syndrome on the Autism Spectrum suffered for a partial or complete deletion of a specific region on Chromosome 2, called MBD5.  This deletion was not found in any of the 7,878 control subjects with no psychiatric diagnosis. Other symptoms of MBD5 deletion include intellectual disability, epilepsy, and significant speech impairment. The size of the deletion is directly correlated with the severity of these manifestations. The team also found that this deletion also impacts RNA. RNA is vital for carrying instructions from DNA to other areas of the body. Individuals who are suffering from RNA imparts are only functioning at approximately 50% of their genetic capacity. Their bodies are only using half their road maps. This team hopes to help improve the quality of life of those suffering from this particular deletion through continuing research.

To read more about Chromosome 2, please see this video and article by PBS or this article by SFARI.

I know this article seems condensed, but there is a lot of information to absorb about Chromosome 2. I think this research is very interesting and may be very beneficial for use in future ASD and related therapies.

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