Serum PEDF levels were measured by ELISA in 6 OI patients with SERPINF1 mutations, 6 carriers of one copy of the SERPINF1 mutation, 88 OI patients with COL1A1, CLO1A2, IFITM5 and other pathogenic mutations of OI and 24 healthy controls.
To date, all patients with the uncommon c.119C>T mutation have presented with severe OI, rather than OI type V. Thus, this report further strengthens the case for a genotype-phenotype correlation for IFITM5-related OI.
In contrast to "classical" forms of osteogenesis imperfecta (OI) types I to IV, caused by a mutation in COL1A1/A2, OI type V is due to a gain-of-function mutation in the IFITM5 gene, encoding the interferon-induced transmembrane protein 5, or bone-restricted interferon-inducible transmembrane (IFITM)-like protein (BRIL).
Furthermore, a single point mutation (c.119C>T) in the coding region of IFITM5 was identified in OI patients with more severe symptoms than patients with OI-V.
After 2006, mutations were identified in the CRTAP, FKBP10, LEPRE1, PLOD2, PPIB, SERPINF1, SERPINH1, SP7, WNT1, BMP1, and TMEM38B genes, associated with recessive OI and mutation in the IFITM5 gene associated with dominant OI.
The genetic mutation resulting in osteogenesis imperfecta (OI) type V was recently characterised as a single point mutation (c.-14C > T) in the 5' untranslated region (UTR) of IFITM5, a gene encoding a transmembrane protein with expression restricted to skeletal tissue.
Our finding has important consequences for the genetic "work-up" of patients suspected to have OI, both in prenatal and in postnatal settings: The entire gene-not only the 5'-UTR harboring the "classical" OI type V mutation-has to be analyzed to exclude a causal role of IFITM5.
Osteogenesis imperfecta (OI) types V and VI are caused, respectively, by a unique dominant mutation in IFITM5, encoding BRIL, a transmembrane ifitm-like protein most strongly expressed in the skeletal system, and recessive null mutations in SERPINF1, encoding pigment epithelium-derived factor (PEDF).
We report a 5-year-old child with clinical features of OI type III or severe OI type IV (characteristic facies, gray sclerae, typical fractures) and absence of classical features of OI type V with a de novo recurrent IFITM5 mutation (c.-14C > T), now typical of OI type V. This highlights the variability of OI caused by IFITM5 mutations and suggests screening for mutations in this gene in most cases of OI where type 1 collagen mutations are absent.