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What Causes Autism? Understanding The Reasons Causing Autism

Autism is a developmental and neurological disorder which occurs in during early childhood. While nobody exactly knows the reason for it, with years of research and studies we have been able to figure out the various known factors that can be the causes of autism. Out of these, the most common ones include genetics, vaccinations, ante-natal and perinatal factors, environmental factors, gut issues and some theories that suggest the role of heavy metals. However, we still cannot rule out any specific causes of autism and mostly rely on these probable factors that could have contributed to the risk of developing Autism. Understanding these factors has given some idea as to how they increase the tendency of a child to develop autism.

Genetic Causes of Autism

Genes seem to have a significant influence in developing Autism. Studies do suggest that autism has a strong connection with the genetic variation and heritability. Various genotypes have been related to cause autism. The fact that it is more common in identical twins gives us substantial evidence of the role of genes in causing autism. Also, if there is any known case in the family, the chances of having autism is higher in the other kids.
A consanguineous marriage (Married in blood relation) increases the probability of having autism, indicating the role of similar genetic coding as an important factor. In the genetic study of kids having autism, we have seen certain gene mutations are commonly found and are known to cause developmental, cognitive and intellectual disorders.

There are various chromosomal duplications or deletions which are related to Autism. Some of the common genetic mutations found in autism are:

  • fragile x
  • 22q13 deletion
  • 1q21.1 microdeletion
  • chromosome 18 deletion (Distal 18q deletion syndrome)
  • chromosome 15 deletion (15q13.3 microdeletion)
  • chromosome 15 duplication (Duplication of 15q11-13 chromosome region) Chromosome 22 duplication, etc.

Most of these chromosomal mutations are known to cause intellectual disabilities, delayed development, learning disabilities, seizures, microcephaly or behavioral issues in children. Genetic screening is therefore advised in a majority of the cases of autism to rule out the presence of any such genetic mutations. If present, genetic testing for both the parents is conducted to find similar genetic changes in either or both the parents. Also, a history of Down’s syndrome has been found in cases of autism.

History of certain psychiatric disorders like depression is commonly seen in the family of kids with autism. Also, kids with autism spectrum are at high risk of developing depression, obsessive-compulsive disorder, and anxiety. So, the genes that make an individual vulnerable to develop a psychiatric disorder might also have some role to play.
Also, there are many cases where we do not find any genetic mutations or known case of autism in the family. Further research work is still being carried out to find a definitive analysis of the role of genes in autism.


There is a strong relationship observed between vaccines and the onset of autism. Sometimes, parents report a regression in the child after a vaccination shot. However, it is unclear what exactly is the role of vaccinations in autism. The most common vaccine that has been a suspected cause of autism is the MMR vaccine. It is a trivalent vaccination preserved in a mercury-based solution and is used against Measles-mumps-rubella virus. The mercury base of this vaccine is also thought to cause autism. Thimerosal is a mercury-based preservative found in many vaccinations. This heavy metal seems to have some toxic effect on the central nervous system (CNS) and increases the risk of autism. In the United States, vaccinations are now being prepared without the mercury or lead-base preservative. There are still some doubts that vaccines do increase the risk of autism in children. But many studies suggest that autism is more common in kids who received vaccination rather than in those who did not.

Pregnancy-Related Causes of Autism 

Some conditions if present during pregnancy can increase the probability of Autism developing in the child. However, it is uncertain how significant a role these factors play in the development of autism. But there are certain conditions which are frequently found in the gestational history of autism cases. Below are some of those common complications or conditions:

Infections during Pregnancy

Infections like German measles or cytomegalovirus if present during pregnancy increases the risk of autism in the child.


Also known as German measles, it can lead to some serious side effects on the baby’s development if a pregnant woman gets infected with it during pregnancy. The infected female might show some flu-like symptoms, for example, a low-grade fever, runny nose, headache, redness of eyes or joint pains. A rash usually follows these flu-like symptoms. It can cause some serious effects on the unborn baby, like congenital rubella syndrome, microcephaly, vision problems, premature baby, miscarriage, or stillbirth. The baby may also be born with some birth defects.

Cytomegalovirus (CMV)

It is a virus which is only carried by humans. Females infected with it mostly do not show any major symptoms, while some might complain of fever, swollen glands, cough or cold. Therefore, it is usually confirmed by the CMV test which is always recommended during pregnancy. CMV might not always have a significant impact on the baby, but in some cases, it can lead to a poor hearing, poor vision and also cause intellectual impairment in the baby.

Gestational Diabetes

When a female develops diabetes (high blood sugar levels) during pregnancy, it is called gestational diabetes. It might not directly lead to autism, but its effects and consequences and can make the baby prone to develop autism. If a mother has diabetes, it can cause hypoxia, growth abnormalities, and the baby can be too large for the gestational age (This can increase the risk of having an assisted/instrumental delivery like vacuum/forceps or C-Section). It can also cause intra-uterine growth retardation and also makes the mother vulnerable to have premature labor. It can trigger the production of excessive insulin by the pancreas of the baby and causes hypoglycemia.
Gestational diabetes also commonly causes depression in pregnant females. A newborn can develop hypocalcemia (low calcium levels) and hypomagnesemia (low magnesium levels). If the diabetes is not controlled during pregnancy, it can also lead to respiratory distress syndrome in the child.

Thyroid during Pregnancy

Having thyroid disorders during pregnancy is very common, and it is not mandatory that the child will develop some developmental issues because of it. However, it is one of the contributing factors which might increase the risk of intra-uterine growth retardation, miscarriage, preterm delivery or low IQ levels of the child. Also, there is some association of thyroxine deficiency which produces changes in the brain of the unborn baby and makes him vulnerable to develop autism.

Usage of Certain Drugs

There have been some drugs identified, whose usage during pregnancy can increase the probability of having autism in the babies. Some of these drugs include anti-epileptic medicine, anti-depressants, and drugs used to prevent premature labor. There is no proven evidence that they do cause autism but it has been observed that their administration increases the risk of autism by three folds. The risk of developing autism is higher especially if the baby is exposed to these drugs during the last months of pregnancy.

Age of Mother at Conception

It is commonly seen that if a woman conceives after or around the age of 40 years, the child is at a higher risk of developing Autism or other developmental issues. Teenage pregnancy is also related to increasing the risk of autism in the child.


Autism is commonly seen in the cases of twin or multiple pregnancies. Gene studies show that there is some relation between twin pregnancy and autism. Autism is especially more common in identical twins than in fraternal twins.

Other conditions

Some other conditions which can increase the risk of autism include depression during pregnancy, oligohydramnios (reduced amniotic fluid), obesity in mothers, smoking, un-natural mode of conception like ovulation therapy, IVF. These factors have been identified in diagnosed cases of autism as a part of the history of pregnancy.

Complications at Birth

Any condition which can cause fetal distress or delay the initial oxygen supply to the brain can be a factor predisposing the child to develop Autism or other developmental delays later. Many conditions are a part of the birth history which are related to autism.

Contributory Conditions

Meconium Aspiration

When a neonate aspirates (breathes in) the stool at the time of birth, it is called Meconium aspiration.
Risk factors for Meconium aspiration include difficult or prolonged labor, post-maturity or advanced gestation age, or if the mother is a smoker. The aspiration of Meconium leads to the obstruction of airways of the fetus. If the aspiration is for a long duration, it causes increased lung resistance, acute Hypoxemia, fetal hypoxia, infection and pulmonary inflammation. The hypoxia at time of birth can lead to autism or other developmental disorders in the child. It also leads to a syndrome commonly known as Meconium Aspiration Syndrome.

Symptoms of Meconium Aspiration include:

  • Bluish/greenish discoloration of the baby
  • Problems with breathing
  • Low heart rate

Hypoxia (Reduced oxygen supply) to the brain

There are various complications at the time of birth that can cause reduced or delayed oxygen supply to the brain of the newborn baby.
This delay in oxygen supply can lead to some significant developmental delays in the child.

Prolonged/Obstructed Labor

Prolonged labor that lasts very long can cause fetal distress, reduction in the fetal heart sound, or hypoxia.

Assisted Delivery

Assisted deliveries that make use of a vacuum pump, or a forceps delivery can be other reasons leading to reduced oxygen supply to the brain. They can also affect the head circumference of the neonate at birth.

Delayed Birth Cry

Another significant sign which indicates reduced or delayed oxygen supply to the brain at birth is a delayed birth cry. It is a critical factor and must be ruled out in every case of autism.

Umbilical Cord Around Neck

An umbilical cord wrapped around a baby’s neck in case of a standard vaginal delivery can have a suffocating effect, again causing fetal distress or reduced oxygen supply.

Hypoglycemia at Birth

Hypoglycemia refers to low blood sugar levels, while neonatal hypoglycemia refers to a temporary drop in blood sugar in infants. It usually occurs at birth or within the first few days after birth. It is one of the common causes of brain injury in infants. The source of glucose during pregnancy is through the placenta, and after birth, it is the breast milk. The liver of the infant also produces a certain amount of glucose. The brain uses sugar or glucose for building up tissues and is an essential source of energy.

Causes of Hypoglycemia

  • Premature babies
  • Kids born to diabetic mother are vulnerable to develop it
  • Production of excess insulin
  • Lack of an adequate amount of breast milk being fed to the baby
  • Insufficient glucose being produced by the baby
  • Intra-uterine growth Retardation
  • Congenital metabolic syndrome
  • Hypoxia at birth

Symptoms of Hypoglycemia

  • Bluish discoloration of skin or Cyanosis
  • Loose muscle tone
  • Breathing issues, it may be fast, or there may be apnea
  • Vomiting
  • Weak cry
  • Low body temperature

If continued for a longer duration, hypoglycemia can result in neurological damage and can also cause any of the following severe conditions:

  • Epilepsy or seizures
  • Brain damage
  • Cerebral Palsy
  • Developmental disorders like Autism
  • Learning Disabilities
  • Affects the Cardio-vascular function

Gut-Related Causes of Autism 

Gut or gastrointestinal issues are some of the most common disorders associated with autism. There are various gut disorders, food allergies, and deficiencies that have been associated with autism. It is difficult to say if they play the causative role, but they contribute to developing autism. Some of the recent research also suggests the role of gut bacteria. Certain gut disorders related to autism are gluten sensitivity, coeliac disease, leaky gut syndrome, milk allergy, chronic constipation, diarrhea and irritable bowel syndrome.
Presence of these gut issues in autistic kids can also increase their behavioral problems. Kids with autism respond very effectively to certain diets, which indicates the role of the gut in autism.

Diets that are gluten-free, casein-free or anti-yeast help in controlling behavioral symptoms, sleep patterns, and hyperactivity in autistic children.

Leaky gut syndrome causes chronic inflammation. Chronic inflammation also seems to trigger some symptoms of autism. The theory behind it is that chronic inflammation decreases the IgA levels. IgA (antibody immunoglobin A) plays an essential role in protecting the body against yeast infections. Yeast is considered to make the child vulnerable to develop sensory concerns that make the child more hyperactive, sleepless and frustrated.
Deficiencies can also be considered as the contributing factors. Children with autism are commonly to found to be low on iron, B12, magnesium, etc. Vitamin B12 plays a vital role in the manufacture of the myelin sheath (layer on nerves), carbohydrates, and production of neurotransmitters. Low magnesium levels produce symptoms like poor focus and concentration, poor memory issues, tremors, muscle cramps, twitches and generalized seizures.

Heavy Metal Load

Many neurological disorders have been associated with heavy metal toxicity. Exposure to certain heavy metals has been found to increase the risk of autism. Mercury, Lead, Aluminum, and Zinc are the most common ones.
High levels of mercury may cause brain damage and increase the probability of neurodevelopmental delays. It doubles the risk of developing autism.
Mercury is commonly found in various vaccinations as a preservative, especially in hepatitis-B vaccine and MMR.
Fish is also a good source of mercury, eating an excess of fish can also raise mercury levels.
There are also reports that if the mother is exposed to heavy metals or pesticides during pregnancy, it can affect the mental development of the fetus inside the womb.

Seizure / Epilepsy

A seizure is a brain disorder which occurs due to excessive or abnormal neuronal activity in the brain. Epilepsy is a disorder where when one has a tendency of recurrent seizures.
About one-fifth of kids with autism have an associated epileptic history. It can’t be exactly said that epilepsy causes autism or autism increases the chances of epilepsy. But both share some relation.
Kids with epilepsy are more prone to develop autism. And there are some changes in the brain of the autistic kids which predispose them to develop epilepsy or seizures.
A family history of epilepsy is also found in cases of autism, showing some relation between the two. Treating seizures in autism also helps lower the severity of the developmental delays and cognitive symptoms.

There are also some genetic changes associated with autism in which we find epilepsy to be an important feature. A sleep EEG can help detect epileptic activity in children.

Environmental Causes of Autism 

Certain environmental conditions like air pollution, extreme cold weathers, and exposure to environmental chemicals during pregnancy can increase the risk of developing autism. Common environmental toxins like herbicides, insecticides or pesticides are harmful to the brain development of the baby in the womb. So, if a female is exposed to all these (especially during the last trimester of pregnancy), the probability of developing autism gets increased.

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