Autism Genetics

The incidence and prevalence of autism are increasing yet the disorder is still not well understood. Because of the murky nature of autism, affected families grasp for any explanation no matter how scanty the evidence. Most experts agree that autism is a complex disease caused by a combination of environmental and genetic factors.

Aubrey Noelle Stimola of the American Council on Science and Health wrote recently in The New York Times (May 15, 2005),

Generally speaking, most experts agree that autism is likely due to numerous and complex genetic factors, many of which may be acted upon by environmental influences. Perhaps it will even be determined one day that some of these genetic factors predispose some autistics to particular sensitivities, maybe even to heavy metals, casein, gluten, loud noises, bright lights, infectious diseases, or any of the countless other environmental influence that have been associated with autism. And perhaps awareness of these sensitivities, all of which should be researched, will be the basis for the alleviation of symptoms. But the fact will remain that these factors are not causative in and of themselves.

The hunt for genes involved in autism is hindered by the difficulty in defining clear diagnostic criteria for the disorder. However, these are some of the latest scientific studies identifying possible autism candidate genes (more studies can be found by searching under autism gene in PubMed):

1. As many as 15+ genes may be involved. Chromosomes 7q, 2q, and 15q and the genes for GABRB3 and serotonin transporter (Santangelo SL and K Tsatsanis, Am J Pharmacogenomics, 2005; 5(2):71-92)
2. Chromosome 2q31.1 (Romano V, et al., Psychiatr Genet. 2005 June; 15(2):149-150)
3. Centaurin gamma-2 (CENTG2) gene on chromosome 2q37.3 (Wassink TH, et al., Am J Med Genet B Neuropsychiatr Genet, May 12, 2005)
4. GRIN2A and ABAT genes on chromosome 16p (Barnby G, et al., Am J Hum Genet, 2005 Jun, 76(6):950-66)
5. Tryptophan hydroxylase gene (TPH2) (Coon H, et al., Am J Med Genet B Neuropsychiatr Genet. 2005 May 5;135(1):42-6)
6. Human leukocyte antigen class III C4BQ0 (Odell D, et al., Hum Immunol, 2005 Feb; 66(2):140-5.
7. LAMB1 and NRCAM genes on chromosome 7q (Bonora E, et al., Eur J Hum Genet. 2005 Feb;13(2):198-207)
8. GABRB3 on chromosome 15q11-q13 (Samaco RC, et al., Hum Mol Genet. 2005 Feb 15;14(4):483-92. Epub 2004 Dec 22)
9. Neurofibromatosis-1 (NF-1) locus (Marui T, et al., Am J Med Genet B Neuropsychiatr Genet. 2004 Nov 15;131(1):43-7)
10. Reelin gene (RELN) on chromosome 7q22 (Skaar DA, et al., Mol Psychiatry, 2004 Nov 23)
11. Glutamate receptor 6 gene (GluR6) (Shuang M, et al., Am J Med Genet B Neuropsychiatr Genet. 2004 Nov 15;131(1):48-50)
12. GABA(A) receptor subunit cluster on chromosome 15q12 (McCauley JL, et al., Am J Med Genet B Neuropsychiatr Genet. 2004 Nov 15;131(1):51-9)

Autism is a multifactorial disease involving both genetic and environmental factors. The environmental factor most discussed, however, is thimerosal in vaccines. While the role of thimerosal in autism etiology is debatable, it would be wrong to ignore all else just to have something on which to dump all our fears and blame. It is akin to focusing only on sugar in type 2 diabetes morbidity even though diet, exercise, and genetics are all contributory factors.

Don’t get lost in the forest just because you’re only climbing one tree. And, don’t let that one tree cause you to break a bone in a completely unexpected place.