Osteogenesis imperfecta type V: Marked phenotypic variability despite the presence of the IFITM5 c.-14C>T mutation in all patients

Background: Osteogenesis imperfecta (OI) type V is an autosomal dominant bone fragility disorder that we had described a decade ago. Recent research has shown that OI type V is caused by a recurrent c.-14C>T mutation in IFITM5. In the present study, we assessed all patients diagnosed with OI type V at our institutions for the presence of the IFITM5 mutation. Methods: IFITM5 exon 1 was analysed by Sanger sequencing in genomic DNA from 42 patients with OI type V (age: 2-67 years; 18 female). Results: The c.-14C>T mutation of IFITM5 was detected in all individuals. Indicators of disease severity varied widely: Height z-scores (n=38) ranged from -8.7 to -0.1, median -3.5. Median final height was 147cm in men (N=15) and 145cm in women (N=10). Lumbar spine areal bone mineral density z-scores in the absence of bisphosphonate treatment (n=29) were between -7.7 and -0.7, median -5.3. Scoliosis was present in 57%, vertebral compression fractures in 90% of patients. Conclusions: Even though the disease-causing mutation is identical among patients with OI type V, the interindividual phenotypic variability is considerable.