Spondylocarpotarsal Synostosis Research Articles

Expanded clinical spectrum of spondylocarpotarsal synostosis syndrome and possible manifestation in a heterozygous father

We report on a 5-year-old boy with spondylocarpotarsal synostosis (SCT) syndrome who presents with disproportionate short stature, thoracic scoliosis, pes planus, dental enamel hypoplasia, unilateral conductive hearing loss and mild facial dysmorphisms. Radiographs showed abnormal segmentation of the spine with block vertebrae and carpal synostosis. In addition to the typical phenotype of SCT syndrome, he showed pronounced delay of carpal bone age and bilateral epiphyseal dysplasia of the proximal femora. The patient's father has mild short stature and unilateral hip dysplasia. Molecular studies of the filamin B gene (FLNB) revealed a homozygous mutation in the index patient while both parents were heterozygous for the mutation. In this report we expand the phenotype of SCT syndrome in a patient with a causal FLNB mutation.

Disruption of the Flnb gene in mice phenocopies the human disease spondylocarpotarsal synostosis syndrome

Spondylocarpotarsal synostosis syndrome (SCT) is an autosomal recessive disease that is characterized by short stature, and fusions of the vertebrae and carpal and tarsal bones. SCT results from homozygosity or compound heterozygosity for nonsense mutations in FLNB. FLNB encodes filamin B, a multifunctional cytoplasmic protein that plays a critical role in skeletal development. Protein extracts derived from cells of SCT patients with nonsense mutations in FLNB did not contain filamin B, demonstrating that SCT results from absence of filamin B. To understand the role of filamin B in skeletal development, an Flnb-/- mouse model was generated. The Flnb-/- mice were phenotypically similar to individuals with SCT as they exhibited short stature and similar skeletal abnormalities. Newborn Flnb-/- mice had fusions between the neural arches of the vertebrae in the cervical and thoracic spine. At postnatal day 60, the vertebral fusions were more widespread and involved the vertebral bodies as well as the neural arches. In addition, fusions were seen in sternum and carpal bones. Analysis of the Flnb-/- mice phenotype showed that an absence of filamin B causes progressive vertebral fusions, which is contrary to the previous hypothesis that SCT results from failure of normal spinal segmentation. These findings suggest that spinal segmentation can occur normally in the absence of filamin B, but the protein is required for maintenance of intervertebral, carpal and sternal joints, and the joint fusion process commences antenatally.

Filamin B represses chondrocyte hypertrophy in a Runx2/Smad3-dependent manner

FILAMIN B, which encodes a cytoplasmic actin binding protein, is mutated in several skeletal dysplasias. To further investigate how an actin binding protein influences skeletogenesis, we generated mice lacking intact Filamin B. As observed in spondylocarpotarsal synostosis syndrome patients, Filamin B mutant mice display ectopic mineralization in many cartilaginous elements. This aberrant mineralization is due to ectopic chondrocyte hypertrophy similar to that seen in mice expressing Runx2 in chondrocytes. Accordingly, removing one copy of Runx2 rescues the Filamin B mutant phenotype, indicating that Filamin B is a regulator of Runx2 function during chondrocyte differentiation. Filamin B binds Smad3, which is known to interact with Runx2. Smad3 phosphorylation is increased in the mutant mice. Thus, Filamin B inhibits Runx2 activity, at least in part, through the Smad3 pathway. Our results uncover the involvement of actin binding proteins during chondrogenesis and provide a molecular basis to a human genetic disease.

Unusual facies, thumb hypoplasia, distinctive spinal fusions and extraspinal mobility limitation, in a pair of monozygotic twins

We report a pair of monozygotic twins with unusual facies and hypoplastic thumbs associated with progressive spinal fusion and joint immobility. The radiographic features were neither consistent with the multiple synostosis syndrome of Herrmann, nor with the spondylocarpotarsal synostosis syndrome. The overall spinal radiographic abnormalities seen in our patients were suggestive of an exceptionally early onset of Forestier disease (anterolateral, perivertebral, ligament ossification), but the thumb hypoplasia and pterygium colli are not seen in that condition. We report what might be a novel genetic entity.

Atlanto-axial rotatory fixation in a girl with Spondylocarpotarsal synostosis syndrome

We report a 15-year-old girl who presented with spinal malsegmentation, associated with other skeletal anomalies. The spinal malsegmentation was subsequently discovered to be part of the spondylocarpotarsal synostosis syndrome. In addition, a distinctive craniocervical malformation was identified, which included atlanto-axial rotatory fixation. The clinical and the radiographic findings are described, and we emphasise the importance of computerised tomography to characterize the craniocervical malformation complex. To the best of our knowledge, this is the first clinical report of a child with spondylocarpotarsal synostosis associated with atlanto-axial rotatory fixation.

Spondylocarpotarsal synostosis syndrome: MRI evaluation of vertebral and disk malformation

Spondylocarpotarsal synostosis syndrome (SSS) is a rare autosomal recessive condition characterized primarily by vertebral malsegmentation, carpal/tarsal coalition, and a dysmorphic appearance. Differentiating SSS from other congenital scoliosis syndromes requires evaluation of the vertebrae, ribs, soft tissues, and spinal cord. The enhanced resolution over plain radiographs seen with MRI allows more detailed assessment of vertebral malformation and surrounding anatomy. Diagnosis of the underlying cause of congenital scoliosis might be enhanced using this technology. We report on a 12-year-old girl of unaffected parents with SSS who was evaluated with MRI sequences of the spine to show various types of malsegmentation. Additionally, there is the new finding of fusion of teeth, with developmental failure of a canine incisor.

Spondylocarpotarsal synostosis syndrome (with a posterior midline unsegmented bar)

Spondylocarpotarsal synostosis syndrome (SSS) is characterised by malsegmentation of the thoracic spine and carpal/tarsal fusions. A unilateral or bilateral unsegmented bar may be present in the thoracic spine. Presenting clinical signs are congenital scoliosis early in life, and shortening of the trunk with scoliosis and/or lordosis in older children. We report a 13-year-old girl with SSS and a midline unsegmented bar running along the spinal processes of T3 to L2 and extending into the posterior vertebral elements.

Spondylocarpotarsal synostosis with ocular findings

We report on three sibs presenting with spondylocarpotarsal synostosis, short-trunk dwarfism of postnatal onset, scoliosis, unsegmented thoracic vertebrae with unilateral bar, and carpal bone fusion. Tarsal bone fusion and dental abnormalities were noted in some of them, indicating pleiotropy and intrafamilial variability. Lens opacities, rarefaction of retinal pigmentation, and narrowing of retinal vessels, detected in two patients, are findings that have not been described to date in this condition.

Spondylocarpotarsal synostosis with ocular findings

Spondylocarpotarsal synostosis with ocular findings

Spondylocarpotarsal synostosis syndrome (with or without unilateral unsegmented bar)

Spondylocarpotarsal synostosis syndrome is characterized by autosomal recessive inheritance, failure of normal spinal segmentation causing symmetrical block vertebrae or scoliosis, and lordosis. There is a disproportionately short trunk. Some patients have a unilateral unsegmented bar. Other skeletal changes include carpal synostosis, usually capitate-hamate and lunate-triquetrum. Tarsal synostoses were present in patients in whom the feet were radiographed. Stature is short. The feet are flat. Cleft palate and sensorineural or mixed hearing loss are variable manifestations. We have reviewed the literature and present 6 new patients, 2 of them sibs.