Causes
There is rarely one single cause of cerebral palsy. For most babies born with cerebral palsy, the cause remains unknown.
For a long time, it was believed that cerebral palsy was due to complications at birth, including asphyxia (lack of oxygen). Researchers now understand that this contributes to only a very small percentage of cases of cerebral palsy.
Now, it is generally accepted that cerebral palsy usually arises from a series of ‘causal pathways’, i.e. a combination of events that can lead to an injury in a baby’s developing brain.
In 13 out of 14 cases of cerebral palsy in Australia, the brain injury leading to cerebral palsy occurs either in the uterus (while the mother is pregnant) or before 1 month of age. At present, the cause is not well understood for most of these babies.
Stroke is the most common cause in babies who acquire cerebral palsy after 1 month of age. The stroke may occur spontaneously or arise from surgical or heart complications.
Risk Factors
Some risk factors for cerebral palsy have been identified. These include:
- premature birth
- low birth weight (small for gestational age)
- blood clotting problems (thrombophilia)
- an inability of the placenta to provide the developing foetus with oxygen and nutrients
- RH or A-B-O blood type incompatibility between mother and baby
- infection of the mother with German measles or other viral diseases in early pregnancy
- bacterial infection of the mother, foetus or baby that directly or indirectly attacks the infant's central nervous system
- prolonged loss of oxygen during the pregnancy or birthing process, or severe jaundice shortly after birth.
It is important to understand that even if a mother or infant does have any of these risk factors, it doesn’t mean that this will definitely result in cerebral palsy. It just means that the chance of having a child with cerebral palsy is increased.
Who is at Greatest Risk?
The Australian Cerebral Palsy Register Report 2009 identified four groups that, statistically, have a greater risk of cerebral palsy.
1. Males - Males are at greater risk of having cerebral palsy.
2. Premature babies - Prematurity is associated with higher rates of cerebral palsy. 42% of children with cerebral palsy are born prematurely, compared to 8% of the Australian population.
3. Small babies - Low birth weight is associated with higher rates of cerebral palsy. This may be a result of prematurity or slow intrauterine growth. 43% of children with cerebral palsy had low birth weight, compared to just over 6% of the Australian population.
4. Twins, triplets and higher multiple births - Multiple births are associated with higher rates of cerebral palsy. 11% of children with cerebral palsy were from a multiple birth, whereas the rates of multiple births are only 1.7% in the Australian population.
Is There A Genetic Link?
For many years, the common understanding has been that cerebral palsy cannot be inherited, and this is basically true. Familial cerebral palsy is uncommon; approximately 1% of people with cerebral palsy will have a sibling with the condition. It is even uncommon in twins – when one twin has cerebral palsy, 90% of co-twins will not have cerebral palsy. However small these statistics, they are enough to suggest that there might be some genetic factors involved in cerebral palsy.
Researchers generally believe that a genetic disposition to characteristics such as:
- prematurity
- small size for gestational age; and
- heart problems ...
... may start a chain of events (a causal pathway). The combination of one or several events along a pathway can result in a child having cerebral palsy.
Any number of problems can occur in the neonatal period when key organs are still developing. For example, a baby in utero may have a genetic predisposition to prematurity and then contract a virus or infection. The baby’s immune system may not respond appropriately which may in turn lead to a premature birth. This baby may need intensive care after birth, but then progress well. It might not be until they reach 6-12 months of age, when developmental milestones are not reached, that a diagnosis of cerebral palsy is made. In this case, it becomes difficult to say that any one factor caused the cerebral palsy. Some children who have a genetic predisposition to a known risk factor might not experience any other events that lead them on one of the pathways that result in cerebral palsy.
In 10% of children with cerebral palsy, brain malformations are present (where the injury to the developing brain happens very early in development). It is thought that this group, as well as those who have had a neonatal stroke (due to inherited thrombophilia), are the most likely to have genetic factors involved.
Families often ask, “I have had one child with cerebral palsy - how likely is it that my next child will also have cerebral palsy?” If you think along the lines of a causal pathway, this is very difficult to answer with certainty. It is likely that your chance is the same as for the first baby. What that chance is, we are unable to tell. For the population as a whole, the chance of having a baby who has cerebral palsy is 1:500. For some, this chance might be higher.
To discuss your concerns, it is advisable to seek genetic counselling before conceiving your next child.
Can Cerebral Palsy Be Prevented or Cured?
At present, there is no way to totally prevent or cure cerebral palsy.
Two interventions are now being used to reduce the risk or severity of cerebral palsy:
- Magnesium Sulphate – is given to pregnant mothers when they are at risk of very preterm birth. This can help protect babies from the brain injury that leads to cerebral palsy.
- Cooling Cap – Newborn babies who have suffered a brain injury due to lack of oxygen before birth (hypoxic ischemic encephalopathy) may be treated with a special cooling cap which aims to reduce the impact of the brain injury.
Brain Plasticity
Recent exciting advances in research have shown that the brain is ‘plastic’ – that is, the brain changes with every different activity it performs. When certain parts of the brain are damaged, sometimes other areas of the brain can, and will, take over to compensate for the injury.
This offers great hope that gene and stem cell therapies may one day be used, even before a baby is born, to repair some or all of the damage to the developing brain that leads to cerebral palsy.
References
Australian Cerebral Palsy Register (2009). Australian Cerebral Palsy Report 2009: Birth years 1993-2003 [PDF]. Sydney.
Jacobs SE, Hunt R, Tarnow-Mordi WO, Inder TE, Davis PG (2007). Cooling for newborns with hypoxic ischaemic encephalopathy, Cochrane Review
Krigger, K W (2006). Cerebral palsy: an overview. American Family Physician, Vol 73, No. 1, pp 91-100
