Treatment response to long term antiresorptive therapy in osteogenesis imperfecta type VI: does genotype matter?

Osteogenesis imperfecta type VI (OI VI) follows a progressive and severe course, yet unlike other forms of severe OI it has a later onset of fractures, and extra-skeletal findings are not part of the clinical picture. Another difference is that there is an increase in unmineralized osteoid tissue in OI VI, which hinders the effect of bisphosphonates-the current standard of treatment for OI. Therefore, the response to standard treatments in OI VI is not satisfactory. Herein, we report long-term follow-up of two cases with novel SERPINF1 mutations, who show great variation in their treatment response to bisphosphonates.

The first case was given pamidronate at the age of 15 months when he could sit independently, followed a fluctuating course under treatment, fracture rate did not decrease, however he was able to mobilize with walker at the age of 10 years. On the other hand, the second case developed severe deformities and became wheelchair-bound under pamidronate, thus the treatment was switched to denosumab. Unfortunately, there was no improvement under denosumab after 15 months too, and since bone pain increased, denosumab treatment was stopped. He was put on zoledronic acid instead.

SERPINF1 transcript amount may be an important factor to explain the variation in response to pamidronate therapy. In OI VI patients, the factors affecting the clinical course should be identified and new or combined treatment options should be established.