Scoliosis is a medical condition defined by an abnormal, sideways curvature of the spine, usually developing during a child’s growth spurt just before puberty. The most common form, Adolescent Idiopathic Scoliosis (AIS), accounts for approximately 80% of cases. The term “idiopathic” signifies that no single, identifiable cause has been determined. Because scoliosis often appears to run in families, the question of its inheritance pattern—whether it is recessive or dominant—frequently arises. Scientific evidence indicates that AIS does not fit the straightforward, single-gene patterns of classic Mendelian inheritance. Instead, the genetic picture is far more intricate, involving the combined effect of many genes and other factors.
The Genetic Reality of Scoliosis Inheritance
The inheritance of Adolescent Idiopathic Scoliosis is best described as a complex trait, meaning it is influenced by multiple factors rather than a single gene. This complexity requires moving beyond the simple categories of dominant or recessive inheritance, which only apply when a trait is controlled by a single gene pair. AIS is classified as a polygenic and multifactorial condition, reflecting the involvement of numerous genetic and environmental components.
The term polygenic means that many different genes work together, each contributing a small risk, to influence the likelihood of developing the condition. No single gene has enough power to cause scoliosis on its own, which is why a simple dominant or recessive label is inadequate. This cumulative effect of multiple genetic variants explains why the condition can appear with variable severity, even within the same family.
The condition is also considered multifactorial, meaning that an individual’s genetic predisposition must interact with other, non-genetic factors for the condition to manifest. These non-genetic influences may include hormonal changes, biomechanical forces, or various environmental exposures. Researchers describe AIS using a multifactorial-threshold model, where a person must accumulate a certain number of risk factors—both genetic and environmental—to cross a “threshold” and develop the spinal curve.
This model of inheritance is further complicated by the concept of low penetrance and variable expression. Penetrance refers to the probability that a person with the genetic predisposition will actually show the physical trait. For AIS, penetrance is low, meaning many individuals carry the risk genes but never develop scoliosis. Variable expression means that even among those who do develop the curve, the severity can range widely, from a mild curve to a severe deformity requiring surgery.
Distinct Categories of Scoliosis and Their Genetic Links
Scoliosis acts as an umbrella term, encompassing several distinct types of spinal curvature, each with a different genetic origin. While the most common form, AIS, is polygenic, other less common categories of scoliosis can follow clearer inheritance patterns. These are typically classified as Congenital Scoliosis or Syndromic Scoliosis.
Congenital Scoliosis is present at birth, resulting from a failure of the vertebrae to form correctly during fetal development. This type is generally caused by structural abnormalities in the spinal bones themselves, such as a vertebra that is only partially formed or two vertebrae that are fused together. While environmental factors during pregnancy can play a role, some cases are linked to specific gene mutations that disrupt early skeletal development.
Syndromic Scoliosis occurs when the spinal curve is a secondary feature of a known genetic disorder. In these cases, the inheritance pattern of the underlying syndrome dictates the genetic risk for scoliosis. For example, several disorders that cause syndromic scoliosis follow a clear autosomal dominant inheritance pattern.
These include Neurofibromatosis Type 1 (NF1), a disorder that affects nerve tissue growth, and Marfan Syndrome, a connective tissue disorder. Autosomal dominant inheritance means that a child only needs to inherit one copy of the mutated gene from one parent to inherit the syndrome and the associated risk for scoliosis. In these specific syndromic cases, the pattern of inheritance is much more defined than in the general AIS population.
Identifying Specific Genetic Markers
Current research efforts focus on pinpointing the specific genetic variations that contribute to the overall risk of Adolescent Idiopathic Scoliosis. The primary tool used for this large-scale search is the Genome-Wide Association Study (GWAS), which compares the entire DNA of thousands of individuals with and without scoliosis. This method has successfully identified numerous regions in the human genome, or loci, that are associated with increased susceptibility.
Researchers have implicated several chromosomal regions, including loci on chromosomes 6, 9, 16, and 17, as potential risk areas for AIS. Within these regions, specific candidate genes like LBX1, GPR126, and CHD7 have been identified as important contributors to the disease. These genes are often involved in biological functions, such as skeletal development, nerve function, and connective tissue integrity.
The challenge in this research is that each identified gene contributes only a small fraction to the overall risk of developing scoliosis. This means there is no single “scoliosis gene” to be found; instead, it is the accumulation of multiple low-risk variants that raises an individual’s susceptibility.
This polygenic architecture has led to the development of commercial genetic screening tools. These available tests analyze a panel of DNA markers to calculate a patient’s risk of curve progression, typically yielding a numerical score. It is important to understand that these tests predict the likelihood of an existing curve worsening, not whether a person will develop scoliosis in the first place. The results only provide a prediction of risk, not a guarantee of future spinal development.
Calculating Familial Risk
The polygenic and multifactorial nature of Adolescent Idiopathic Scoliosis translates into a significantly elevated, but still non-guaranteed, risk for family members. Population studies show that the general risk of developing AIS is approximately 2% to 3%. However, this risk increases substantially for first-degree relatives—parents, siblings, and children—of an affected individual.
For a first-degree relative, the probability of also developing scoliosis is notably higher, with studies suggesting a risk of around 11%. For a sibling of an affected person, the risk can be even higher. This increased risk is a direct result of inheriting a greater number of the contributing risk genes.
The familial pattern is also demonstrated by twin studies, which show that identical twins have a much higher concordance rate for scoliosis (around 73%) compared to fraternal twins (approximately 36%). This difference highlights the strong genetic influence.
Because of this elevated familial risk, early and regular screening is highly recommended for children who have first-degree relatives with scoliosis. While the genetic risk cannot be changed, early detection of a spinal curve allows for timely interventions like bracing, which can prevent the curve from progressing to a severity that might require surgical correction. This proactive approach is the most actionable step families can take to manage the inherited predisposition.