Is cerebral palsy an inherited syndrome? Does the disorder run in families? Can it be passed from parent to child by way of genetic information, like eye color? These questions have dogged medical researchers for decades; their answers remain poorly understood.
The Complex Link Between Genetics & Cerebral Palsy
We know that a large proportion of cerebral palsy cases are caused by fetal brain damage, usually sustained during the second or third trimesters of pregnancy. Maternal infections, for example, can be transmitted to a developing fetus and ultimately damage the brain tissue relevant for neuromuscular function. We also know that a significant subset of cases are primarily the result of oxygen deprivation that occurs during the labor and delivery process. These causal factors give “acquired” cases of cerebral palsy their name, as opposed to “congenital” forms of the disorder that develop prior to birth.
Twin Studies & Siblings
However, a growing body of research has shown that some cases of cerebral palsy do appear to have genetic anomalies as their primary cause.
Studies of twins, for example, who share the same genetic code, have proven a particularly fertile area of research. In one large 2014 study of over 2 million Norwegian births, public health scientists at the University of Bergen found that, if one twin was born with cerebral palsy, the risk of the second twin being born with the disorder increased nearly 16-fold.
This trend appeared to extend even to non-twin siblings. In families with one “singleton” child who had been diagnosed with cerebral palsy, the risk of a subsequent child being born with CP was around 9.2-times higher than in the general population. So too for half siblings, who were around 3-fold more likely to develop the condition. Importantly, when the researchers controlled for preterm births, an important risk factor for cerebral palsy, the association between genetic similarity and CP actually strengthened.
High Incidence Of Congenital Anomalies
Indirect evidence for the genetic foundations of cerebral palsy have come in other forms as well. For example, the rate of congenital anomalies in people with cerebral palsy is far higher than rates among the general population.
As researchers at the Genomic Medicine Institute noted in 2012, between 11% and 32% of children diagnosed with cerebral palsy are found to have other conditions associated with genetic abnormalities, from cerebral disorders like microcephaly to congenital heart malformations. In members of the general population, congenital anomalies are far less prevalent, occurring in between 2% and 3% of people.
Moreover, studies of familial descent have found higher rates of cerebral palsy among children born to “consanguineous” parents, ones who come from the same blood line.
In fact, the risk among children born to parents who share a common lineage may be up to 250% higher than in parents who found their partners Assuming that cerebral palsy is correlated with genetic mutations, this is precisely the result one would expect to find. Consanguineous parentage conserves genetic traits, rather than bumping up genetic diversity.
Strong Genetic Component Isn’t End Of The Story
Most researchers now agree that cerebral palsy has a strong genetic component, though there is no single gene that can predict the disorder’s development.
Overwhelming scientific evidence shows that cerebral palsy disorders are not associated with a single genetic trait that can be passed from parent to child. Thus, cerebral palsy is not a heritable disease, at least not in the simple sense that we consider eye or hair color to be inherited traits. The link between heritable genetic mutations and cerebral palsy appears to be more complicated than that.
Scientists have found evidence that a number of different genes (six so far) appear to be involved in the condition, which could explain why cerebral palsy affects different children in extremely different ways. In reality, cerebral palsy refers to a spectrum of related disorders – each with a unique presentation – much as we have come to understand autism in recent decades. As scientists say, cerebral palsy is a “heterogeneous” diagnosis, encompassing a diverse array of neurodevelopmental disorders.