Genetic Testing

Autism has no single known cause. Several explanations have been proposed, and research has not established any of them. Causes of some symptoms of autism, on the other hand, can be determined through a process called genetic testing.

Genetic testing is a medical test that can identify changes in chromosomes, genes, and proteins. It is done to confirm or rule out a certain condition or help determine a person’s chance of passing on or developing such a condition. A medical geneticist evaluates a genetic test.

Types of Genetic Testing

Gene tests

Gene testing is a test that examines a person’s Deoxyribonucleic Acid (DNA). DNA is a large double-stranded, helical molecule that is the carrier of genetic information. This test is conducted by getting a sample from a person’s blood or other body fluids such as saliva or tissues. It detects any structure abnormalities, quantity abnormalities, presence or absence of a gene.

Biochemical tests

Biochemical tests are often used for newborn screening wherein certain metabolic disorders such as Phenylketonuria (PKU) are determined. It is a test that basically looks at the amount of activity of key proteins.

Chromosomal tests

A chromosomal test is a test that examines a person’s chromosomes, which are large DNA-containing structures in the nucleus of a cell. Changes, such as deletion of some chromosomal pieces and expansion or switching of chromosomal location, are determined during this test. Two common chromosomal tests are:

Karyotyping - This is a test that takes a picture of all chromosomes of a person. It is designed to identify any changes in the chromosomal number and significant changes in DNA structure. An example of a disorder determined by karyotyping is Down syndrome, wherein there is the presence of an extra copy of chromosome 21.

Fluorescent in situ hybridization, or FISH analysis: this is a test that identifies small missing or extra pieces of specific chromosomes. An example of a disorder that FISH can determine is the velocardiofacial syndrome, wherein chromosome 22 is missing fragments.

For a child diagnosed with autism, doctors today usually recommend chromosomal microarray, which finds small missing or extra pieces across all the chromosomes at once, and fragile X testing first (American College of Medical Genetics and Genomics, 2013). Many now also offer exome sequencing. These tests find a genetic cause in a minority of children, more often when the child also has an intellectual disability or other medical signs.

Through genetic testing, it can be determined if any autism-related symptom, such as metabolic disorder that your child has, is due to a genetic disorder or has no known genetic cause. If a genetic cause is found, a genetic counselor can tell the family the chance of it happening in another pregnancy. For some causes the chance is high; for a change that is new in the child, it is low. For instance, phenylketonuria has a reoccurrence risk of 1:4 or 25%. Even when no genetic cause is found, a younger brother or sister of an autistic child is more likely to be autistic: about 1 in 5 in a large study of infant siblings (Ozonoff et al., 2011), and higher for boys and when more than one older sibling is autistic. Many genes, each with a small effect, together with non-genetic factors, are thought to explain this.

Reference:   http://www.nlm.nih.gov/medlineplus/ency/article/001526.htm

Ozonoff, S., et al. (2011). Recurrence risk for autism spectrum disorders: A Baby Siblings Research Consortium study. Pediatrics, 128(3), e488–e495.

Schaefer, G. B., & Mendelsohn, N. J. (2013). Clinical genetics evaluation in identifying the etiology of autism spectrum disorders: 2013 guideline revisions. Genetics in Medicine, 15(5), 399–407.

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