Sumio Goto

Mutation in Npps in a mouse model of ossification of the posterior longitudinal ligament of the spine

Ossification of the posterior longitudinal ligament of the spine (OPLL) is a common form of human myelopathy caused by a compression of the spinal cord by ectopic ossification of spinal ligaments. To elucidate the genetic basis for OPLL, we have been studying the ttw (tiptoe walking; previously designated twy) mouse, a naturally occurring mutant which exhibits ossification of the spinal ligaments very similar to human OPLL (Refs 3,4). Using a positional candidate-gene approach, we determined the ttw phenotype is caused by a nonsense mutation (glycine 568 to stop) in the Npps gene which encodes nucleotide pyrophosphatase. This enzyme regulates soft-tissue calcification and bone mineralization by producing inorganic pyrophosphate, a major inhibitor of calcification. The accelerated bone formation characteristic of ttw mice is likely to result from dysfunction of NPPS caused by predicted truncation of the gene product, resulting in the loss of more than one-third of the native protein. Our results may lead to novel insights into the mechanism of ectopic ossification and the aetiology of human OPLL.

Effect of decompression enlargement laminoplasty for posterior shifting of the spinal cord.

STUDY DESIGNnA study to measure the shifts of the spinal cords and the effects of decompression laminoplasty in 65 patients with cervical lesions who underwent computed tomographic myelography before and after laminoplasty.nnnOBJECTIVESnTo investigate limitations of the spinal cord posterior shift after laminoplasty and to clarify the optimal decompression areas to obtain effective posterior shifting.nnnSUMMARY OF BACKGROUNDnAlthough several types of laminoplasty have been performed, all procedures share the common purpose of posterior decompression. No previous studies have examined the limitations of posterior decompression or the optimal decompression range.nnnMETHODSnThe distance from the posterior edge of each vertebral body or disc level to the posterior edge of the spinal cord was measured by computed tomographic myelography. After the posterior shift was determined by calculating the difference between pre- and postsurgical distances, the relations between posterior shift and neck alignment, clinical results, and the areas of decompression were analyzed.nnnRESULTSnThe spinal cord shift ranged from a maximum of 6.6 mm to a minimum of 0 mm. Clinically, spinal cord shifts greater than 3 mm were associated with good clinical outcomes. Upward or downward advanced laminoplasty was related to larger spinal cord shifts at the upper or lower cervical spine.nnnCONCLUSIONSnA mean spinal cord shift of > 3 mm was associated with good clinical outcomes after laminoplasty. In cases with compressive lesions at the upper or lower cervical spine, extension of decompression one level above or one level below likely results in a greater posterior spinal cord shift at these lesions.

Association of the human NPPS gene with ossification of the posterior longitudinal ligament of the spine (OPLL).

Abstract OPLL (ossification of the posterior longitudinal ligament of the spine) is a common form of human myelopathy with a prevalence of as much as 4% in a variety of ethnic groups. To clarify the genetic factors that predispose to OPLL, we have studied ttw (tiptoe walking), a mouse model that presents ectopic ossification of the spinal ligaments similar to OPLL and have found that the ttw phenotype is caused by the nonsense mutation of the gene encoding nucleotide pyrophosphatase (NPPS), a membrane-bound glycoprotein thought to produce inorganic pyrophosphate, a major inhibitor of calcification and mineralization. To investigate a possible role of NPPS in the etiology of OPLL, we have examined its genetic variations in OPLL patients. A total of 323 OPLL patients was screened by means of polymerase chain reaction/single-strand conformation polymorphism analysis covering all the exons and their surrounding introns, plus about 1.5-kb of the promoter region. We identified ten nucleotide variations in the NPPS gene; five of the alterations caused amino-acid substitutions, and two of them were found specifically in OPLL patients. Subsequently, we performed an association study using these variations and found a significant association of an allele, viz., a deletion of T at a position 11 nucleotides upstream from the splice acceptor site of intron 20 (IVS20–11delT), with OPLL; the proportion of the individuals having this deletion was significantly higher (P = 0.0029) in OPLL patients than in controls, indicating that those who have this variation may be more susceptible to the abnormal ossification of the spinal ligaments. Thus, our study suggests that NPPS plays an important role in the etiology of human OPLL.

Three-dimensional Motion Analysis of the Upper Cervical Spine During Axial Rotation

Rotational motion of the normal upper cervical spine was analyzed in 20 men using biplanar roentgenograms, a system digitizer, and a personal computer. To detect the bony landmarks of the atlas, the subjects heads were fixed and their trunks rotated in the reference frame while these biplanar studies were obtained. Coupling motions observed included 10 degrees extension at C0-C1, with 11 degrees of lateral bending between C1-C2. Almost all (80%) cervical axial rotation took place at C1-C2, whereas only 4 degrees of rotation occurred at C0-C1. Furthermore, as C1-C2 axial rotation increased, so did rotation in the opposite direction at C0-C1 while less rotation was noted below C2. The instantaneous axis of rotation was located anterior to the foramen magnum at the C0-C1 level, in the central portion of the dens at C1-C2.

Bone Morphogenetic Protein-2 Stimulates Differentiation of Cultured Spinal Ligament Cells from Patients with Ossification of the Posterior Longitudinal Ligament

Ossification of the posterior longitudinal ligament (OPLL) of the spine is characterized by heterotopic bone formation occurring in spinal ligament, causing severe compression myelopathy. In order to investigate the mechanism of OPLL development, we isolated spinal ligament cells from OPLL patients as well as non-OPLL patients, and established 10 OPLL cell lines and 7 non-OPLL cell lines, respectively. We analyzed the effects of bone morphogenetic protein-2 (BMP-2) on these cells with respect to alkaline phosphatase (AP) activity, DNA synthesis, and collagen production. BMP-2 caused a significant increase of AP activity in 4 OPLL cell lines, whereas the activity did not change in any non-OPLL cells. Among OPLL cells, BMP-2 stimulated DNA synthesis in four cell lines and procollagen type I carboxyl-terminal peptide (PICP) synthesis in five cell lines. Some non-OPLL cells also responded to BMP-2, as there was an increase of DNA synthesis in three cell lines and PICP synthesis in one cell line. These data collectively indicate that BMP-2 preferentially induces osteogenic differentiation in OPLL cells rather than in non-OPLL cells. OPLL cells, therefore, exhibit a different response to BMP-2 than non-OPLL cells, suggesting that the expression of BMP receptor(s) and/or the signal transduction initiated by BMP-2 in the spinal ligament cells of OPLL patients somewhat deviate from those in normal spinal ligament cells. Such abnormal characteristics of OPLL cells as described here provide some clues to the clarification of the pathogenesis of OPLL.

Long-term follow-up evaluation of surgery for ossification of the posterior longitudinal ligament.

Study Design. We compared anterior and posterior surgery for cervical myelopathy resulting from ossification of the posterior longitudinal ligament. Surgical techniques, based on shape and distribution of ossification of the posterior longitudinal ligament, were divided into four technical phases. Objectives. Long-term follow-up data on anterior and posterior surgery were analyzed to establish guidelines for surgical treatment. Summary of Background Data. Comparison of anterior and posterior surgery is difficult because surgical techniques, ossification of the posterior longitudinal ligament shape classifications, and surgical criteria varied. No reports have accurately assessed spinal changes over a 10-year follow-up period. Methods. Fifty patients received anterior surgery and 65 received posterior surgery between 1968 and 1993. Assessment after surgery was based on the recovery rate using the scoring system of the Japanese Orthopaedic Association. Spinal changes in the anterior group were assessed radiographically. Results. Recovery and final results improved with phase after anterior, but not posterior, surgery. Neurologic deterioration after initial recovery was lower for the anterior group. One third of patients in the anterior group followed for more than 7 years exhibited neurologic deterioration, with most showing these changes within 10 years. Worsening was attributed to insufficient removal of lateral, superior, or inferior, or inferior ossification of the posterior longitudinal ligament, reossification at the excision site, kyphotic malalignment, growth of ossification at upper cervical levels, or untreated complicated hypertrophy of the posterior longitudinal ligament. Many patients showed a good outcome after surgery. Accurate alignment and long-range fusion improved results. If the cord was compressed in a canal narrowed to under 3 mm, anterior surgery was considered “too risky.” Conclusions. Complete extirpation of ossification of the posterior longitudinal ligament as confirmed by ultrasonography during surgery and long-range fusion with fibular grafts is advocated in the management of ossification of the posterior longitudinal ligament.

The Extent of Ossification of Posterior Longitudinal Ligament of the Spine Associated with Nucleotide Pyrophosphatase Gene and Leptin Receptor Gene Polymorphisms

Study Design. A case-control study using radiograph findings and the PCR assay with regard to the susceptibility and the severity of ossification of posterior longitudinal ligament of the spine (OPLL). Objective. To analyze whether polymorphisms of the nucleotide pyrophosphatase (NPPS) gene and the leptin receptor gene predispose to an increased frequency and severity of OPLL. Summary of Background Data. The NPPS gene is responsible for ectopic ossification in the ttw mouse, an animal model for OPLL. The Zucker fatty rat, another animal model for OPLL, has a missense mutation in the leptin receptor gene. Methods. Analysis of 172 OPLL patients and 93 non-OPLL controls was performed. Radiographs of the cervical, thoracic and lumber spine were analyzed to determine whether OPLL was present and to what degree. Genomic DNA was extracted from all participants. Polymorphisms of the NPPS gene and the leptin receptor gene were analyzed using the PCR assay. The association of the polymorphisms with the development and extent of OPLL were statistically evaluated. Results. No significant association was found between the polymorphisms and the existence of OPLL in both the NPPS and the leptin receptor genes. However, the IVS20–11delT variant in the NPPS gene and the A861G variant in the leptin receptor gene were more frequent in patients with OPLL in the thoracic spine compared with patients whose OPLL was restricted to the cervical spine. Conclusion. The present results suggest that the IVS20–11delT variant of the NPPS gene and the A861G variant of the leptin receptor gene are associated with more extensive OPLL, but not with the frequency with which it occurs.

Relationship between bone mineral density of the proximal femur and lumbar spine and quadriceps and hamstrings torque in healthy Japanese subjects

The purpose of this study was to examine the corelations between the muscle torque of the leg extensors (quadriceps femoris) and leg flexors (Hamstrings) and the bone mineral density (BMD) of the proximal femur and lumbar spine. To investigate the decline in BMD of proximal femur and lumbar spine, we examined the relative importance of muscle torque, age, and body weight in the prediction of BMD in 340 healthy volunteers (109 males, and 231 females). Age and body weight were independent predictors of femoral BMD in men. Body weight and quadriceps torque were independent predictors of femoral BMD in premenopausal women. Body weight and years after menopause were independent predictors of BMD in postmenopausal women. The BMD was greatly affected by menopause, whereas the muscle torque was independent of the menopause, and showed the negative relationship to age. These results suggest that muscle-building exercise may have the potentiality to elevate the BMD in the proximal femur in premenopausal women.

Juvenile amyotrophy of the distal upper extremity : Pathologic findings of the dura mater and surgical management

Study Design. Five cases of juvenile amyotrophy of the distal upper extremity were reviewed retrospectively to elucidate the pathophysiology of spinal cord dysfunction and the results of surgical management. Objectives. To clarify the pathogenesis of juvenile amyotrophy of the distal upper extremity and to present the results of a new surgical treatment. Summary of Background Data. Hirayama first reported this disorder in 1959. It is characterized by juvenile onset, slow progression, and involvement of the unilateral distal upper extremity. Recently, compression of the cervical spinal cord during neck flexion was implicated as a possible etiology of the disorder, but the exact etiology is still unknown. The value of surgical treatment for patients with juvenile amyotrophy of the distal upper extremity has not been established. Methods. The clinical and radiographic characteristics of five patients with juvenile amyotrophy of the distal upper extremity were examined. All five patients were treated surgically with duraplasty in combination with posterior spinal fusion. Dynamic and computed tomographic myelography were performed before and after surgery. Intraoperative ultrasonography and conductive spinal cord evoked potentials were recorded before and after duraplasty. The surgical results and the histology of the resected dura were studied. Results. Myelograms taken with the neck in a neutral position showed that the spinal cord was flattened in all five patients. When the neck was flexed, the dura and the spinal cord were compressed further. Intraoperative ultrasonography during neck flexion revealed an anterior shift of the spinal cord and decreased spinal cord pulsation. Amplitude of the conductive spinal cord evoked potentials decreased with neck flexion but in creased after dural incision. Histologically, the dura appeared abnormal in that it contained few elastic fibers without the normal wavy structure. Conclusions. Juvenile amyotrophy of the distal upper extremity was characterized by inelastic dura that constricts and compresses the cervical spinal cord when the neck is in either a neutral or a flexed position. Abnormal dura appeared to be the cause of juvenile amyotrophy of the distal upper extremity. Duraplasty with spinal fusion are proposed as treatments.

Anterior surgery in four consecutive technical phases for cervical spondylotic myelopathy.

Between 1960 and 1990, 175 patients having anterior operations for cervical spondylotic myelopathy were evaluated during the course of four operative phases. Specific attention was paid to spine and spinal cord morphologic changes occurring in 52 patients, who were followed up for more than 12 years. Although overall outcomes were satisfactory, a disturbing incidence of neurologic deterioration caused by spondylolisthesis at levels adjacent to fused segments, kyphosis, and altered cord morphology was noted 10 years after surgery. These changes, observed in patients with multilevel pathology and a narrowed spinal canal, prompted the adoption of more stringent operative criteria, including ultrasonically confirmed 16-mm or greater anterior trough decompressions and the performance of long fusions with vascularized fibular struts.