The WNT1G177C mutation specifically affects skeletal integrity in a mouse model of osteogenesis imperfecta type XV

The recent identification of homozygous WNT1 mutations in individuals with osteogenesis imperfecta type XV (OI-XV) has suggested that WNT1 is a key ligand promoting the differentiation and function of bone-forming osteoblasts. Although such an influence was supported by subsequent studies, a mouse model of OI-XV remained to be established. Therefore, we introduced a previously identified disease-causing mutation (G177C) into the murine Wnt1 gene. Homozygous Wnt1G177C/G177C mice were viable and did not display defects in brain development, but the majority of 24-week-old Wnt1G177C/G177C mice had skeletal fractures. This increased bone fragility was not fully explained by reduced bone mass but also by impaired bone matrix quality. Importantly, the homozygous presence of the G177C mutation did not interfere with the osteoanabolic influence of either parathyroid hormone injection or activating mutation of LRP5, the latter mimicking the effect of sclerostin neutralization. Finally, transcriptomic analyses revealed that short-term administration of WNT1 to osteogenic cells induced not only the expression of canonical WNT signaling targets but also the expression of genes encoding extracellular matrix modifiers. Taken together, our data demonstrate that regulating bone matrix quality is a primary function of WNT1. They further suggest that individuals with WNT1 mutations should profit from existing osteoanabolic therapies.

Osteogenesis imperfecta: a literature review and a clinical case of a perinatal-lethal type of disease

The article presents the modern views of clinicians and geneticists on one of the most severe genetic disorders of skeletal and connective tissues - osteogenesis imperfecta. The review provided the literature data that showed the incidence rates, genetic heterogeneity of osteogenesis imperfecta, as well as the role of some proteins involved in the construction of bone tissue, as well as a clinical classification of the main types of the disorder. The authors described a clinical case: a girl with typical clinical and radiological manifestations of the rarest of all types of osteogenesis imperfecta - type II (perinatal-lethal, congenital osteogenesis imperfecta, Vrolik’s syndrome). The child’s diagnosis was verified by a parallel DNA sequence analysis which showed a heterozygous mutation in exon 29 (c.1966G> A) of COL1A1 gene not previously described in the literature. It caused the substitution of glycine for serine at position 656. The role of antenatal diagnostics and the importance of medical genetic counselling of the family before planning the next pregnancy due to the existing risk of re-birth of a sick child is outlined. Due to the fact that majority of the patients with the most prognostically unfavourable type II osteogenesis imperfecta, as a rule, die in utero, the described case of observation of the girl with typical clinical and X-ray signs of the disorder for almost 3 months of postpartum period is extremely rare and highly indicative. The detection of the heterozygous mutation in exon 29 (c.1966G > A) of COL1A1 gene by a parallel DNA sequence analysis which was not previously described in the literature gives an additional significance to the described observation.

A RARE CASE OF OSTEOGENESIS IMPERFECTA TYPE I

A 7 year old female patient was admitted to hospital having experienced bowing of upper and lower limbs, repeated fractures over the past 4 years. Clinical ndings and radiological investigations such as recurrent fractures and deformity of bones while bearing weight, blue sclera and low bone mineral density, all led us to conclude that this child has a mild form of osteogenesis imperfecta type I. The patient was immediately started on calcium (1000mg/day), vitamin D (800mg/day) and pamidronate (60mg) was given intravenously. Following the above protocol, we found that the quality of life of the patient showed signicant improvement. This patient is a rare case of OI type I.