Friday, July 25, 2014

Understanding Genetics: Chromosome 16

This is the eighth entry in the series Understanding Genetics. I hope you have been enjoying the overview of just a few of hundreds of genes linked to Autism. We have been covering the most prevalent and scientifically significant chromosomes so far. On our journey to becoming well educated advocates for our loved ones, we have covered many topics, this being the most challenging for me. I love a challenge. So, with the end of our series coming up, let’s get underway in understanding Chromosome 16.

Chromosome 16 has approximately 90 million DNA pairs and represents approximately 3% of the total DNA in every cell. Scientists believe chromosome 16 contains 800-900 genes that provide instructions on making proteins, which play a role in various roles in bodily function. Additions and deletions of chromosome 16 cause a vast number of disorders and are now believed to also impact Autism. 

A 16p11.2 deletion occurs near the middle of chromosome 16. Individuals with this deletion usually have developmental and intellectual delay, and most exhibit some features of ASDs. Expressive language, or the ability to speak, can be severely impacted, but receptive language may be intact. Other individuals may have minor physical abnormalities like low-set ears or webbed toes. It should be noted that no particular pattern of physical abnormalities indicate this deletion, the physical abnormalities listed are simply the most common in occurrence. Any combination of these along with developmental or intellectual delay can indicate this deletion. The prevalence of this deletion is approximately 3 in 10,000 and most are not genetically inherited. 

In 2008 MedPage Today published an article, Chromosome 16 Mutations Linked to Autism. Researchers in Boston studied 2,252 patients with ASD and compared them with 22,200 controls. Researchers found that in most cases mutations appear to be spontaneous, rather than inherited. These errors occur during early development and usually result in a duplication of chromosome 16. In the cases of inheritance they suggest some complexity, since the parents carry the duplication, but are not necessarily Autistic themselves. In some of these parents the mutation may manifest itself as a different disorder, such as ADHD. Researchers estimate the rate of mutations appears to be approximately 1% of those with ASD, compared to approximately 0.01% of the general population.

In a 2009 SFARI article, chromosome 16, previously dobbed the key to the Autism region was not what researchers once thought. This article references a study of 45 people published in the Journal of Medical Genetics and another study of 77 individuals published by the Journal of Neurodevelopmental Disorders. Both studies found that the most common symptom of people carrying a chromosome 16 variant are speech delay and cognitive impairment. This implies that chromosome 16 may not be as big of a player in the genetics game as science once believed, but it should be counted out all together. There is still a link between chromosome 16 and Autism, but it may fall into a supporting role to other genes. 

In 2010 SFARI published another article discussing the link between chromosome 16 ties Autism to obesity. Referencing two studies published in Nature, chromosome 16, associated with Autism, is also linked to obesity and may manifest itself as both disorders in one individual. This article estimates that chromosome 16 deletion occurs in approximately 0.6% of all Autism cases. One of these studies shows that approximately 3% of those with both obesity and developmental delay disorders also carry the chromosome 16 deletion. Doctors have long noticed that individuals with developmental delay also have a tendency to be overweight. A report was published by Obesity in the January 2010 found that 23.4% of children with Autism are obese, compared to approximately 12.2% of typical children.

Chromosome 16 has interesting links to Autism. It may not be as prevalent in every individual, but it certainly does impact a statistically significant portion of the total ASD population. We hope this article has helped to you to add one more tool to your advocacy tool box. 


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