autism spectrum disordersAutism spectrum disorders are a range of conditions categorized in the diagnosis of autism. Autism is one of most prevalent but poorly differentiated diagnoses because it is a loosely connected collection of genetic disorders of unknown origin. The common elements of Autism Spectrum Disorders (ASD) is a profound learning disability and mental retardation, which varies greatly from one affected individual to another. Because of high heterogeneity in clinical manifestations it is very difficult to provide more precise diagnosis, let alone to find an effective treatment. However, recent genetic analyses of Autism Spectrum Disorders identified specific disease-causing genetic alterations and provide interesting insights on potential treatments.

How genetic testing helps with the diagnosis of Autism Spectrum Disorders

Genetic analyses of Autism Spectrum Disorders identified even greater heterogeneity of Autism – each family harbors a unique set of disease-causing variants explaining why clinicians have such difficulty diagnosing and treating the disease. However, these studies show great growth for the personalized treatment of Autism.

In these studies 10% contribution to Autism Spectrum Disorders risk by spontaneous mutations (de novo mutations) in genes are associated with the fragile X protein, FMRP, reinforcing links between autism and synaptic plasticity. Intriguingly the frequency of de novo mutations is related to paternal age – older fathers have a higher risk of conceiving autistic child.

Additional studies indicted that about 6% of Autism Spectrum Disorders cases are due to new large scale changes in chromosomes that affect gene copy number (de novo CNVs ). About 5% of Autism Spectrum Disorders cases are caused by complete disruption of gene function – 3% of which are distributed across various chromosomes and 2% are affecting predominantly boys since they occur on the X-chromosome.

Genome analysis, and particularly exome sequencing, show that mutations in many neuronal genes can cause autism – such as mild mutations in PEX7, SYNE1, VPS13B, PAH, POMGNT1. These genes play important but distinct roles in neuronal signaling or brain development. For each affected child the mutation is different and requires different treatment strategy.

Example of a Autism Spectrum Disorders Case

One example is a child affected by Autism Spectrum Disorders has a milder defect in the AMT gene that affects metabolism of glycin – important amino acid that regulates neuronal signaling. Patients with severe mutations in AMT typically present with Glycin encelopathy or nonketotic hyperglycinemia (NKH) – excess in glycin in blood (Applegarth and Toone, 2004). Classical NKH is severe genetic disease that leads to death within first year of life due to progressive lethargy, hypotonia, and severe seizures (Hamosh and Johnston, 2001). Elevated levels of glycin in patients with mild AMT mutation lead to delays in expressive language, behavioral problems, and only small subset has seizures. Therefore, it is possible to find ways to reduce glycin levels through special diets or treatment that reduce glycin absorption from food.

Some common medications could be re-purposed for treating neuronal diseases. For example treatment of mice genetically engineered to mimic the Fragile X disorder with lovastatin alleviated the abnormal neuronal activity by correcting the protein synthesis, opening possibilities that one day some children might benefit from simple and proven medications.

Such studies are greatly increasing the speed of translation of research discoveries to clinical practice. Personalized genetic diagnostics of Autism Spectrum Disorders is important to find correct and optimal treatment strategy for each child.

What’s next?

If you would like to learn more about autism, continue reading this related blog post: “What Causes Autism in Children?”.

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