A sideways-curving spine is the most troubling aspect of scoliosis, but it’s not the real problem. To figure out what actually causes scoliosis, scientists must look beyond the curve.
We now know that spinal curvature stems from a miscommunication between the brain and the muscles that support the spine. The child’s postural control centers fail to tell the muscles how to properly respond to gravity, so instead of growing straight the spine becomes curved. But why aren’t those messages being sent?
It’s a question with which doctors continue to grapple. Is scoliosis genetic? Hereditary? Caused by environmental factors? Most of the time there’s no clear answer, and that’s what makes scoliosis such a difficult condition to treat.
In about 20 percent of cases, the scoliosis causes are obvious; birth defects, bone damage and neuromuscular disorders can all cause spinal curves to form. But they’re a small minority. More than eight in 10 scoliosis cases are idiopathic, which means they have no known cause.
Through decades of research, scientists have been able to piece together a number of observations and findings about adolescent idiopathic scoliosis. But so far those findings have defied any unified theory to explain why one child’s curve progresses rapidly while another’s requires no medical attention at all.
“Adolescent idiopathic scoliosis probably results from a combination of genetic and environmental factors,” says the National Institute of Health. “Studies suggest that the abnormal spinal curvature may be related to hormonal problems, abnormal bone or muscle growth, nervous system abnormalities, or other factors that have not been identified.”
Is Scoliosis Hereditary or Genetic?
Strong evidence suggests that scoliosis runs in families. Nearly a third of patients with adolescent idiopathic scoliosis have a family history of the condition, and first-degree relatives of scoliosis patients have an 11 percent chance of developing it themselves.
“It is possible that genetic factors may be involved in specific aspects of scoliosis, including the shape of a scoliosis curve and the risk for curve progression,” said scoliosis specialist Christopher R. Good, M.D., in the Journal of the Spinal Research Foundation. “A number of population studies have documented that scoliosis runs within families and that there is a higher prevalence of scoliosis among relatives of patients with scoliosis than within the general population.”
The numbers do support the theory that scoliosis is hereditary, or passed down from family members — but does that necessarily mean it’s genetic?
To answer that question, it’s important to understand the difference between genetic and hereditary. Most people use them synonymously, and in many cases they are, but there are subtle differences. A trait can be hereditary without being genetic; cultural characteristics, for example, are passed down through families but aren’t connected to genes. And genetic traits aren’t always hereditary. Consider cancer, which arises from mutant genes but in most cases isn’t inherited from one’s parents.
By examining the inheritance patterns of scoliosis, scientists have concluded that the condition is genetic as well as hereditary, but they still haven’t been able to identify which genes are responsible.
“Researchers suspect that many genes are involved in adolescent idiopathic scoliosis,” says the National Institute of Health. “Some of these genes likely contribute to causing the disorder, while others play a role in determining the severity of spinal curvature and whether the curve is stable or progressive. Although many genes have been studied, few clear and consistent genetic associations with adolescent idiopathic scoliosis have been identified.”
Is Scoliosis Environmental in Nature?
When studying what causes scoliosis, hereditary factors can provide a lot of insight — but they also raise as many questions as they answer.
For example, if scoliosis is hereditary, why does it also crop up in children with no family history of the condition? Another oddity researchers have noted is that the condition seems to have variable effects within each generation. A mother with a mild curve might have a daughter with a severe one, or the scoliosis might skip a generation entirely.
Scientists have explained these anomalies by acknowledging that environmental factors probably contribute to differences in scoliosis development, progression and age at detection. Consider that at least 4 percent of scoliosis curves progress to the threshold for surgery, yet only 1 percent of patients have a high genetic risk of severe curvature. If genes are a factor in only 1 percent of cases, environmental factors must account for the severity in the other 3 percent.
But identifying what those factors are is tricky. Studies have ruled out the theory that the curves are caused by specific behaviors such as slouching or carrying a heavy backpack. They’ve also found no link between scoliosis and living in an industrialized area.
Understanding what causes scoliosis is like hitting a moving target. It’s not a fixed deformity but a dynamic process that appears to spring from a combination of different factors. The more we study it, however, the better equipped we become to effectively treat the condition.