How does Phenylketonuria result in Autism?


Autism is a neuropsychiatric disorder and spread all over the world from 1st world country to the 3rd world. This is the most vital reason to worry about this brain disease. Another reason is the cure of this mental retardation. This is because autism is strongly genetic and is an incurable disorder, unlike the other neurological disorders.

According to the past and present CDC data report, the number and percentage of autistic children have been found at very increased rate in the U.S. So,

# Awareness
# Early Diagnosis
# Proper treatment (knowing that autism is incurable)

are necessary to reduce the autistic symptoms as well as the percentage of autistic children, which is 1 out of 68 children according to the latest 2010 CDC data report.

Many articles are written on it to make people aware about this genetic brain disease. The result is, more or less we know that autism is genetic and many genetic bio-markers responsible for it have also been found.

But there is a problem. People should be aware of autism or ASD (Autism Spectrum Disorders), but misunderstanding or misconception can lead the people or parents of mentally challenged children to the wrong direction of treatment.

The goal of this article is to make people know that all low I.Q patients or children with genetic mutation are not the victims of autism.


In Born Error Metabolism can be responsible for few cases of mental retardation and low I.Q.


What is this In-Born Error Metabolism?

Biochemical reactions occur in stepwise conversion of one substrate to other. Each step has been catalysed by enzyme. Now a mutant gene may produce a defective protein/ enzyme and it will be unable to carry out the reaction properly.

This results in

  • Accumulation of substrate
  • Decreased formation of product
  • Increased production of alternative metabolite

There are many in-born error metabolic diseases. Phenylketonuria is one of them, responsible for the low I.Q and mental retardation of children.


Phenylketonuria: An In-Born Error Metabolic Disease

Deficiency of phenylalanine hydrolase (enzyme) causes accumulation of phenyl alanine. Phenyl alanine is then converted to alternative metabolic product, phenylpyruvic acid.

Clinical Manifestation:
# Appearance of phenylketone in urine
# Increase of phenylalanine in serum level

PKU leads Mental Disabilities
PKU leads Mental Disabilities









Image Courtesy:


# Child shows low I.Q and mental retardation
# Hyperactivity
# Hypo-pigmentation
# Mousy odour in body sweat


Diagnostic Test:

There are several tests to know if a child suffering from low I.Q, mental retardation and hyperactivity is with autistic disabilities or with Phenylketonuria.

The one more simple and effective way to diagnose is ferric chloride test.
In this test, a drop of FeCl3 is added to half field test tube of patient’s urine. A transient blue green colour shows the presence of phenylketone in urine.


We know that the autistic patients now can be treated through restricted diet. Firstly, the known diet for autistic children and patients was GF/ CF diet but now Broccoli and Cannabis are added in the list of restricted diet.

If patients or children with mental retardation are found with Phenylketonuria, then diet with low level of phenylalanine can recover the symptoms.

So, proper diagnosis is needed before you or your patient is going for any treatment. That may be for autism or for the other diseases.

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