Idiopathic scoliosis: how much of a genetic disorder? Report of five pairs of monozygotic twins.

PURPOSE: The role of genetic factors in the development of Adolescent Idiopathic Scoliosis (AIS) has been well documented; however, reports of the specific mode of genetic inheritance are inconclusive. These facts, combined with the phenotypic variability of this disorder, suggest that the genetic expression of idiopathic scoliosis may be dependent on multiple factors and genetic interactions. However, it seems questionable whether there is evidence for a genetic aetiology for adolescent idiopathic scoliosis, when in monozygotic twins there is no 100% concordance of the symptoms and prognosis.

METHODS

Five pairs of monozygotic tested twins with the diagnosis of AIS were presented in the outpatient practice of the author. There was no history of scoliosis in any other member of the family.

RESULTS

Pair 1: Growth is still left in both girls, however prognosis is totally different. The progression factor of the first girl was 1.75 and so she has a risk of >65% for curve progression, Cobb angle 40. Progression factor of the second girl was 0.56 and so she has a risk of <5% for curve progression, Cobb angle 18. Pair 2: Both girls presented with Risser 4. Cobb angle was 55 degrees in one of the twins (progression factor: 3.1; risk for progression >95%) and 220 in the other (progression factor: 0.7; risk for progression <5%). Curve pattern was thoracic in the first, double major in the second girl. Pair 3: Two monozygotic tested boys with similar bad prognoses and similar curve pattern and similar degrees of curvature (90 and 100 degrees). Pair 4: Two not tested girls with similar benign prognoses and similar curve patterns (18 and 22 degrees). Pair 5: Two monozygotic tested girls with different prognoses and similar curve patterns (26 and 49 degrees).

CONCLUSIONS

Different curve patterns in two of the five pairs of twins as well as different prognoses can be discussed as phenotypic variability of AIS, however the findings from the other three pairs may be interpreted in the way that genetic factors play a role in the aetiology of AIS.