A child's snore may sound cute, or even funny, but habitual snoring in children may contribute to problems ranging from bed-wetting to poor school performance.

In fact, some children with sleep disorders associated with snoring are mistakenly diagnosed with attention deficit-hyperactivity disorder, or ADHD, when what they really need is a good night's sleep.

Dr. David Gozal, a professor of pediatrics at the University of Louisville, and director of the Pediatric Sleep Center at Kosair Children's Hospital, has studied the link between learning difficulties and what is known as sleep disordered breathing.

Below, Gozal discusses the signs and symptoms of sleep disordered breathing, and available treatments.

What causes snoring in children?

Snoring in children can result from three things. First, there is an anatomical component, such as a small jaw or a small airway that the child was born with. Secondly, there's the possibility that the muscles and the nerves controlling those muscles are not well integrated during sleep and therefore do not open the airway enough. But the most common reason children snore is enlarged tonsils and adenoids.

How common is the snoring in children?

It's a very common condition. From our studies in the US population and other populations around the world, habitual snoring affects about 11 percent to 12 percent of all children between the ages of 1 through 9.

With habitual snoring, a child will have snoring, at least three to four times a week, that is loud enough that the parents will know about it.

Why should parents of children who are habitual snorers be concerned?

Parents should be aware of it because snoring can be associated with significant disruption of the quality of sleep and other underlying conditions that can affect the brain and the heart.

With habitual snoring, many parents will say, 'Oh, I don't care too much,' and I've had parents who actually were very proud of it, saying, 'My child is a little adult because he snores as strong as his grandpa.'

Well, that's not a funny thing to me. That actually indicates that the child may be having significant problems, and that their snoring needs to be evaluated.

How is snoring different in children than in adults?

The principle is about the same. In other words, snoring is noisy breathing that results from the vibration of air going through the upper airway.

So in itself, it's just a sound. But what it indicates is that there are increases in the upper airway resistance, meaning that the resistance to air passing through the upper airway is high.

During sleep, the muscles go to sleep a little bit, and that relaxation makes the airway collapse a little bit more. Consequently, the same amount of air has to go through a smaller space.

Snoring may reflect other, more serious conditions such as sleep apnea or upper airway resistance syndrome. About 3 percent of all children between the ages of 1 though 9, have sleep apnea or upper airway resistance syndrome, and those conditions can lead to substantial consequences.

What is the difference between upper airway resistance syndrome and sleep apnea?

Children with upper airway resistance syndrome sometimes wake up because of the resistance in the airway, or because their snoring is loud, or because the snoring requires so much effort. But there are no changes in the oxygen levels or the carbon dioxide levels within the blood or in the tissues in the child.

In sleep apnea, the airway sometimes collapses and doesn't open, and the child struggles to breathe and can't get any air in.

As a result, the carbon dioxide goes up, the oxygen goes down, and then finally the child has to wake himself or herself up in order to catch his or her breath. We've seen children with 500 and 600 awakenings in the night just to be able to catch their breath and go back to sleep.

Is chronic snoring in children ever harmless?

We don't know. Snoring is not normal, but that doesn't mean that it always needs to be treated. Clearly, if a child wakes up because of the snoring - that is, if they have upper airway resistance syndrome or sleep apnea - they need to be treated.

What increases risk for sleep apnea in children?

Obesity is the predominant risk factor. If you lay down and you have a mass of fat in your neck, that puts even more pressure on tissues that are already relaxed, and makes the pharynx, or airway, even smaller.

Children who are born into a family that has a high risk of sleep apnea are at increased risk. And children with Down syndrome, children who have significant hypotonia - that means that their muscles are relatively very weak - and children who have neuromuscular diseases are at much higher risk for sleep apnea than other kids.

Obviously, if you get allergies, you get substantial swelling of the lining of the nose, and that can lead to enlargement of adenoids, and altogether this makes it more likely that a child will have difficulty breathing through their nose.

Some kids who are asthmatic, obviously, can have sleep apnea. But if two diseases are common, then they are likely to coincide even though they may not share any common mechanisms.

However, in children whose parents smoke, we see a major risk factor for snoring.

What are some of the short-term consequences of sleep apnea in children?

The short-term consequence of it is very simple. If you have sleep apnea, you wake up after what is called unrefreshing sleep.

You're tired, you have difficulty with concentration, and you feel very groggy in the morning. Through the night children may wet their bed because they're so anxious to sleep that whenever they feel the pressure to urinate, they don't care. This may also lead to nightmares and night terrors.

How does sleep apnea affect behavior and learning?

Children with sleep apnea have difficulty concentrating, and they may, in many ways, behave as if they have attention deficit hyperactivity disorder. For example, kids who don't like to sleep resist sleep by becoming hyperactive. They start fighting with everybody, and then finally they crash.

The next day, these kids are having difficulty paying attention and staying put, and behave as if they have ADHD. We have shown recently that a substantial number of children who are diagnosed with hyperactivity disorder have sleep apnea, and if you treat the sleep disordered breathing their hyperactivity disappears.

Sleep apnea also affects learning.

If you don't sleep well at night and your brain suddenly does not receive enough oxygen, you may start losing brain cells. So during a period of brain development, the cognitive abilities of the children are affected by sleep apnea.

In a study that we did several years ago we found that children who were not doing well in school were much more likely to have sleep apnea than normal children. We also found that if you treated those children for their sleep apnea, their grades came up.

We have also found evidence in some of the studies that we've done, both in children and in animals, that the consequences can be life-lasting. So if you don't treat sleep apnea early enough, then the brain has suffered and this could be an irreversible loss. In other words, children may not be able to compensate, and therefore lose IQ points, for example, that they will never recover.

What are other biological consequences?

When you are going through these episodic periods of awakening and low levels of oxygen, the nervous system also gets turned on and there's a strain on the heart. Over time it may lead to changes in the blood pressure that may, if an individual is predisposed to have hypertension as an adult, lead to much more severe hypertension.

Another consequence is what I call the vicious cycle of sleep apnea and eating. If you don't sleep well, the next day you're much more hungry for calories, especially fast calories such as fat and sugars. And if you're tired, you don't exercise.

You become more obese, and obesity can even make the sleep apnea worse. So that leads to substantial problems with cholesterol, with prediabetic conditions, and risk for cardiovascular disease at a much earlier age.

What are treatments for sleep apnea?

In children, it's a little bit different than it is for adults. In general, adults, because the major cause is obesity, will require a machine that is called CPAP (continuous positive airway pressure).

In other words, there's a little mask with pressure that essentially will keep the airway open.

In children, because the most common reason for sleep apnea is enlarged tonsils and adenoids, the best way to treat sleep apnea is by sending them to an ear, nose and throat surgeon to have them removed. In about 85 percent to 90 percent of the cases, we'll see complete resolution, at least for a few years, of that problem.

That doesn't necessarily mean that sleep apnea will not recur during adulthood.

If surgery is not effective, which is true in about 10 percent of the cases, such as in the more obese children or in those with more severe or complicated conditions, then CPAP and/or BIPAP (bi-level positive airway pressure) are the techniques that we use.

What about orthodontic measures?

That's an important question, because obviously the proportions of how the jaw is positioned is very important in defining the size of the upper airway. There's one study out of Italy that has shown that application of orthodontics can make sleep apnea better in children.

But the first line of treatment in a child with enlarged tonsils and adenoids is to first take care of the tonsils and adenoids, and then if there's residual sleep apnea, I would do the orthodontic treatment.

Is surgery risky in some children with sleep apnea?

There are some groups of children, including the very young, children with severe apnea, or those with other disorders that may be contributing to the sleep apnea, who we usually retain for at least 24 hours' monitoring in the hospital after surgery, instead of doing the procedure as an outpatient procedure.

What advice would you give to parents whose child is habitually snoring? First of all, they should recognize that snoring is not something that we would call a benign condition.

They should be concerned if their child is tired in the morning, has very restless sleep, has difficulty performing at school or has behavioral issues. Other issues are having a lot of nightmares, morning headaches, or, in older children, having a lot of bedwetting that is unexplained.

All of these characteristics, in addition to snoring, should raise the suspicion in the parents that they should pay more attention and have their child seen by a pediatrician and evaluated for potential sleep disorder breathing.