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Sunday, January 27, 2013

Autism and Schizophrenia: Shared Genetics?

Autism (autistic disorder) is a type of neurodevelopmental disorder that causes impairments in social interaction, impairments in communication, and restricted, repetitive, and stereotyped patterns of behavior, interests, and activities.

The onset of autism is always prior to three years of age. Schizophrenia is a neurologically based mental disorder in which one loses contact with reality, experiences abnormal thinking, and has poor emotional responsiveness. The onset of schizophrenia is typically in the late teens to mid 30s.

Unlike autism, schizophrenia does not have an onset prior to age three. In fact, even onset of schizophrenia during adolescence is rare. If schizophrenia does present in childhood/adolescence, it presents after years of normal or near normal development (assuming no other condition is present). It is possible for someone with autism to later develop schizophrenia and some studies (not all) have shown that autism increases the risk for schizophrenia.

Unlike schizophrenia, autism does not present with prominent delusions of hallucinations. A hallucination is a strong sensory perception that one has of an object or event while awake, when no such object or event exists. A delusion is a persistent false belief that is strongly held despite clear evidence that the belief is actually false.

Despite their obvious differences, autism and schizophrenia share some common features. This includes disturbances in language, affect (the outward way a person shows feelings/emotions), and problems relating socially to others. Both conditions are also known to be associated with rare structural genetic abnormalities. These abnormalities are usually copy number variations (CNVs) which mean that a cell has an abnormal number of copies of one or more section of DNA (an abbreviation for deoxyribonucleic acid). DNA is a chain of many connected genes. Genes contain coded instructions for how proteins should be constructed and how certain bodily characteristics should develop. There are many different forms of genes. Each form is known as an allele. Some alleles are normal and others are abnormal. Abnormal alleles can cause diseases.

The above commonalities have led some to question whether autism and schizophrenia have shared genetic abnormalities. Researchers in the American Journal of Medical Genetics: Neuropsychiatric Genetics recently published a study that examined this issue. The study involved analyzing the genes of 2,737 people with autism spectrum disorders (autism and closely related conditions) and 3,332 Europeans with schizophrenia. The authors examined whether autism and schizophrenia shared alleles in common (known as common risk alleles). The results of the study showed that there was no important sharing of common risk alleles between autism spectrum disorders and schizophrenia.

Suggested Reading: Autism: A Practical Guide for Parents

Reference: Vorstman JA, Anney RJ, Derks EM, Gallagher L, Gill M, de Jonge MV, van Engeland H, Kahn RS, Ophoff RA; the Autism Genome Project, the International Schizophrenia Consortium. (2013). No evidence that common genetic risk variation is shared between schizophrenia and autism. Am J Med Genet B Neuropsychiatr Genet. 162(1):55-60.

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