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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