The etiology and pattern of inheritance for the transmission of idiopathic scoliosis remain unknown, though studies of families with multiple affected members suggest that a single gene or limited number of genes are linked to the disease. Recent studies have used an autosomal dominant pattern of transmission, with incomplete penetrance and variable expressivity, to conduct linkage studies [1, 3, 8, 9].
This pattern was also observed in the family studied in this study; however, the high level of consanguinity observed should be highlighted, as well as the fact that the family originates from a small town of approximately 15,000 inhabitants, for this reason, we also have done a linkage analysis considering an autosomal recessive pattern of inheritance and allele frequency of 0.01%. Nevertheless, we did not find any specific chromosome region associated with the disease.
The criteria for characterization of an individual as affected by the disease in the literature includes the presence of scoliosis equal to or greater than 10° as determined by the Cobb method, with vertebral rotation observed in radiographs realized in the frontal position in orthostasis [1–3, 5–9].
Axenovich et al (1999) conducted segregation analysis on 101 families with idiopathic scoliosis patients and observed a monogenic, dominant pattern of inheritance, using a diallelic model, considering individuals with curvature greater than 11° as affected . Wise et al (2000) studied families whose probands presented curves equal to or greater than 50° or who required corrective surgery. Among the families analyzed in previous works, expressive variation was observed in the spinal curve values of affected patients, which suggests the possible influence of other genetic and environmental factors . In the present study, we analyzed affected individuals with a physical exam compatible with idiopathic scoliosis and radiographs indicating curvature equal to or greater than 15°. Individuals suspected of having the disease showed some clinical sign and radiographs suggestive of idiopathic scoliosis, though a curvature greater than 10° was not considered obligatory. Thus, it was possible to construct a heredogram with an autosomal dominant characteristic. The family studied showed characteristics typical of idiopathic scoliosis; notably the individuals were Caucasian and the female members were predominantly affected (100%).
Since 2000, familial studies have been conducted in an attempt to map the chromosome regions responsible for idiopathic scoliosis. Wise et al (2000) suggested that regions on chromosomes 6, 10 and 18 were related to idiopathic scoliosis . Salehi et al (2002) investigated three generations of one family of Italian origin with 11 affected members who presented curves between 10 and 20° and an autosomal dominant pattern of inheritance with complete penetrance . Their study mapped a region of approximately 20 cM on chromosome 17p11 linked to idiopathic scoliosis. In the same year, Chan et al (2002) identified a region of 5.2 cM in the region 19p13 and reported a secondary candidate region on chromosome 2, while studying seven Chinese families with an autosomal dominant pattern of inheritance and probands with curves between 20 and 55° that required the use of a brace or surgical treatment . In 2005, Alden et al also reported a region on chromosome 19 with potential links to idiopathic scoliosis, when studying 1198 individuals from 202 families that presented at least 2 affected members with curves equal to or greater than 11°. However, correlation with region 19p13 only occurred when analyzing families with probands with curvature equal to or greater than 30° . Ocaka et al (2008) studied 25 unrelated multiplex adolescent idiopathic scoliosis families . Of these, 24 families were Caucasian of British descent, and one was of African-Caribbean origin. The authors considered families with at least three affected members who had curves equal to or greater than 10°, with rotation. The probands had curves that required orthopedic treatment, varying 20 and 55°. An autosomal dominant pattern of inheritance with penetrance estimated at 80% was verified. The authors reported two chromosome regions potentially linked to adolescent idiopathic scoliosis on chromosomes 9p34 and 17q25.