Consanguineous-derived homozygous WNT1 mutation results in osteogenesis imperfect with congenital ptosis and exotropia

Type XV osteogenesis imperfecta: A novel mutation in the WNT1 gene, c.620G >A (p.R207H), is associated with an inner ear deformity

The Wnt signaling pathway is vital in encouraging bone growth. WNT1 gene mutations have been identified as the major cause of type XV osteogenesis imperfecta (OI). Described here is a case of complex heterozygous WNT1 c.620G>A (p.R207H) and c.677C >T (p.S226L) OI caused by a novel mutation at locus c.620G >A (p.R207H). The female patient had type XV OI, distinguished by poor bone density, frequent fractures, a small stature, skull softening, lack of dentine hypoplasia, a brain malformation, and obvious blue sclera. A CT scan of the temporal bone revealed abnormalities of the inner ear, necessitating a hearing aid 8 months after birth. There was no family history of such disorders in the proband's parents. The proband inherited complex heterozygous WNT1 gene variants c.677C>T (p.S226L) and c.620G>A (p.R207H) from her father and mother, respectively. Presented here is a case of OI with inner ear deformation caused by c.620G>A (p.R207H), which is a novel WNT1 site mutation. This case broadens the genetic spectrum of OI and it provides a rationale for genetic testing of mothers and a medical consultation to estimate the risk of fetal illness.

Case report: Early-onset osteoporosis in a patient carrying a novel heterozygous variant of the WNT1 gene

The WNT1 gene is crucial for bone development and homeostasis. Homozygous mutations in WNT1 cause severe bone fragility known as osteogenesis imperfecta type XV. Moreover, heterozygous WNT1 mutations have been found in adults with early-onset osteoporosis. We identified a 35 year-old Caucasian woman who experienced multiple vertebral fractures two months after her second pregnancy. There was no history of risk factors for secondary osteoporosis or family history of osteoporosis. Dual-energy X-ray absorptiometry confirmed a marked reduction of bone mineral density (BMD) at the lumbar spine (0.734 g/cm², Z-score -2.8), femoral neck (0.48 g/cm², Z-score -3.5), and total hip (0.589 g/cm², Z-score -3.0). Blood tests excluded secondary causes of bone fragility. Genetic analysis revealed a heterozygous missense mutation (p.Leu370Val) in the WNT1 gene. Varsome classified it as a variant of uncertain significance. However, the fact that the Leucine residue at position 370 is highly conserved among vertebrate species and the variant has a very low allelic frequency in the general population would exclude the possibility of a polymorphism. The patient was treated for two years with teriparatide therapy associated with calcium and vitamin D supplements. During the follow-up period she did not report further clinical fractures. After 24 months of teriparatide, BMD increased at lumbar spine (+14.6%), femoral neck (+8.3%) and total hip (+4.9%) compared to baseline. We confirm that the heterozygous WNT1 mutation could cause a variable bone fragility and low turnover osteoporosis. We suggest that teriparatide is one of the most appropriate available therapies for this case.

Consanguineous-derived homozygous WNT1 mutation results in osteogenesis imperfect with congenital ptosis and exotropia

Background

Wnt signaling pathway plays an important role in promoting ostergenesis. WNT1 mutations have been considered as a major cause of ostergenesis imperfect (OI). We identified an OI patient with pathogenic consanguineous‐derived homozygous WNT1 missense mutation.

Methods

We designed and applied a panel of known 261 genes associated with hereditary bone diseases for targeted next‐generation sequencing to examine clinically diagnosed OI patients. Detected mutations were confirmed by Sanger sequencing.

Results

The female proband presented with severe OI with low bone density, multiple long bone fractures, short stature, and absence of dentinogenesis imperfect and brain malformation. She had congenital ptosis and exotropia with her left eye, and absence of blue sclera. The proband came from a consanguineous family and had a homozygous WNT1 missense mutation (c.677C>T, (p.S226L)). In addition, three other compound heterozygous mutations (c.1729C>T in FKBP10, c.1958A>C in FGFR3, c.760G>C in TRPV4) were also detected in her family members.

Conclusion

We report the first identified case of consanguineous derived homozygous WNT1 mutation leading to severe osteogenesis imperfecta with congenital ptosis and exotropia.