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You may have noticed that your child was different, even as a small baby. Perhaps they seem less involved with the world around them than other children. And may be your child doesn't show much interest in people.

You may be trying to work out if the differences you have noticed are autism. Or you may have been told that your child has autism and want to find out the best way to help them.

• If your child has autism, they may not learn to speak at the usual age. And they may have problems communicating in other ways too.
• Also, your child may not be interested in other people. And they may have set ways of behaving and may do the same activity over and over again.
• Usually, these signs show up before your child is 3 years old.
• We don't know what causes autism. But it's linked to how your child's brain works. It's not caused by anything you as a parent might have done.
• About 6 in 1,000 children have an autistic spectrum disorder. That means they have autism or a related condition. Some children have only mild symptoms and some children have bad symptoms.
• There isn't any cure for autism. Your child will always have it. But getting treatment early on can help make a difference to your child's life.¹
• There hasn't been much good research on which treatment works best.

Children change in many ways as they get older. They grow physically. For example, they put on weight and get taller and stronger.

But they grow in other important ways too. They learn how to speak, smile and get along with people in other ways, such as playing. Doctors call all of these changes development. These changes normally happen by specific ages. So you may hear them called developmental milestones. A milestone is just a way to tell how far you have come.

Doctors watch for milestones to tell if your child is developing properly. You can watch for them too. If you are worried about your child having autism, here are some milestones you can watch for.^{2 3 4 5}

• By the age of 2 months, most babies smile.
• By 9 months, most babies follow your finger if you point to something.
• By 1 year, most babies babble and point to things they want.
• By 2 years, most babies can speak phrases of two words on their own (not copying their parents) and can play pretend.

But children don't always follow this pattern exactly. Also, they can be slow to reach certain milestones but not others. Ask your doctor if you think your child is falling behind in any way.

Skills such as speaking, smiling and getting on are controlled by your brain. It does this through several networks or pathways of nerves that connect your brain to other parts of your body. As your child grows their brain forms new and more pathways so they develop more skills.

With autism, your child's brain doesn't work as it should.¹ This affects how your child develops in many ways. So doctors call autism a pervasive developmental disorder (PDD for short).

On the outside, children with autism usually grow and look like other children. But they don't develop the skills they need to get along well with others or to keep up in school.

With autism, your child usually has problems with speaking. And they may not like being touched in any way, such as cuddling. Also, they may behave in odd ways. For example, your child may do the same activity over and over again. Or they may follow the same routine all the time.

Sometimes, children with autism are very good at a certain skill or subject, such as math, technical drawing or music. That's because they can focus very hard on just one thing. This is linked to their autism. But this happens rarely.

Autism affects different children in different ways. Some children never learn to speak and need help throughout their life. Other children can learn the skills they need to live on their own.

Autism belongs to a group of similar conditions. Doctors call this group autistic spectrum disorder. The group also includes a condition called Asperger's syndrome. To learn more, see Autistic spectrum disorder.

On these pages, we are looking at autism itself.

If your child has autism, you may worry that something you did caused it. But nothing you have done as a parent could have caused your child's autism.

In most children with autism, doctors don't know the exact cause for it.⁶ All we know is that the brains of children with autism work in a different way.¹

Researchers have looked at many factors to see if they are linked to autism. We've described some of these below.

Studies give us good evidence that autism is mainly caused by genes, rather than by any things your baby or child experiences. You get half of your genes from your father and half from your mother. Your genes control how your body develops. If you have a faulty gene, it can cause problems with growth and health. But this doesn't always happen.

A combination of certain faulty genes from both parents may increase a child's chance of getting autism. We're still not sure which genes are involved or how the faulty genes affect your child's brain. We have good evidence from research that autism is mainly caused by genes.

• Some studies have looked at autism in families. When a family has one child with autism, the chance of having another child with autism are about 1 in 20.⁷ This is much higher than we would expect.⁶
• Other studies have looked at identical twins. Identical twins have the same genes. These studies have shown that if one twin has autism, there is a 6 in 10 to 9 in 10 chance that the other twin also has autism.⁸ This is a much higher chance than for nonidentical twins. Nonidentical twins don't have the same genes.

If you already have a child with autism, or you or your partner has an autistic spectrum disorder, you may worry about the chance of your future children also having autism. You can get advice about this from a genetic counselor. This is a person who will look closely at your family. Ask your doctor about genetic counseling.

The genes your child has may not be the only reason for their autism. Things your child goes through in the womb, at birth or afterward, might help bring on the condition. Autism probably happens because of a combination of genes and these other things. But researchers haven't found any good evidence for this. So we can't say for sure.⁹

Sometimes autism is caused by a medical condition that your child gets. But this isn't common.⁸ In about 1 in 10 children with autism, the autism is clearly caused by a medical condition.⁹ To learn more, see Medical causes of autism.

In the past, some experts thought that vaccination with the MMR vaccine (a vaccine for measles, mumps and rubella) might be linked to autism. Because of the worry, many parents have decided not to give their children this vaccine. But several big studies have looked into this question. All these studies have said there isn't any evidence of a link between the MMR vaccine and autism.

Leading researchers and doctors who specialize in child health advise parents to give their children the MMR vaccine.^{8 10 11 12}

To learn more, see MMR vaccine and autism.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.