|Year : 2015 | Volume
| Issue : 1 | Page : 96-100
Smith-McCort variant syndrome: A rare case with associated enamel hypoplasia
Sandeepa Nuchilakath1, Jaishankar Homberhalli Puttabuddi2
1 Department of Oral Medicine and Radiology, KVG Dental College, Sullia, Karnataka, India
2 Department of Oral Medicine and Radiology, JSS Dental College, Mysore, Karnataka, India
|Date of Submission||01-Aug-2014|
|Date of Acceptance||08-Jan-2015|
|Date of Web Publication||12-Oct-2015|
Department of Oral Medicine and Radiology, KVG Dental College, Sullia - 574 327, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
The Smith-McCort syndrome (SMC), which was first described by Smith and McCort in 1958, is a rare form of osteochondrodysplasia, specifically a spondyloepimetaphyseal dysplasia. It is one of the rare syndromes that can present with skeletal dysplasia and mimic some of the common bone diseases. Enamel hypoplasia is a part of this disorder. Literature that describes the orofacial characteristics of this syndrome is lacking. Here we report a case of a 23-year-old female, who presented with characteristic orofacial features, along with skeletal abnormalities.
Keywords: Enamel hypoplasia, osteopenia, spondyloepimetaphyseal dysplasia
|How to cite this article:|
Nuchilakath S, Puttabuddi JH. Smith-McCort variant syndrome: A rare case with associated enamel hypoplasia. J Indian Acad Oral Med Radiol 2015;27:96-100
|How to cite this URL:|
Nuchilakath S, Puttabuddi JH. Smith-McCort variant syndrome: A rare case with associated enamel hypoplasia. J Indian Acad Oral Med Radiol [serial online] 2015 [cited 2020 Feb 19];27:96-100. Available from: http://www.jiaomr.in/text.asp?2015/27/1/96/167125
| Introduction|| |
Spondyloepimetaphyseal dysplasias (SEMD) are a heterogeneous group of chondrodysplasias, characterized by different patterns of inheritance.  Different subtypes of SEMD are reported in genetic medical databases and literature. The Smith-McCort variant syndrome (SMS) is one of the subtypes of SEMD (subtype II). SMS is a rare autosomal recessive osteochondrodysplasia characterized by short limbs and a short trunk, with a barrel-shaped chest.  Here we report a case of SMS, presenting with characteristic orofacial and radiographical features.
| Case Report|| |
A 23-year-old female patient reported to us with a main complaint of pain in relation to her upper and lower back teeth region, since six months. The pain aggravated on taking hot and cold food and persisted after removal of the stimulus. Her past medical history revealed chest abnormalities and joint pain, for which the patient had undergone various investigations in her childhood. She was the second child of a healthy family and her parents had a consanguineous marriage. She was born at full-term, with no complications. When the patient presented to us, she was undergoing physiotherapy for the joint pain.
On general physical examination, the patient was with short stature, short neck, and prominent lower third of the face. Her height was 130 cm. Pigeon chest was present and it was noted by the parents since birth. Lumbar lordosis was also evident in the patient. Syndactyly was present in the left lower limb. The upper and lower limbs were proportionate [Figure 1].
|Figure 1: Clinical photograph showing short statured patient and syndactyly on the left lower leg|
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Intraoral examination revealed generalized enamel hypoplasia and deep carious lesions in relation to 26 and 46. Root stumps were present in relation to 46 [Figure 2]a and b.
|Figure 2: (a) Clinical photograph showing enamel hypoplasia of upper teeth (b) Clinical photograph showing enamel hypoplasia of lower teeth|
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The provisional diagnosis given was chronic pulpitis in 26 and 46. Her general features led to include a list of bone disorders in the diagnosis. Rickets, Morquio disease, and achondroplasia were considered, in view of her skeletal and dental abnormalities.
A panoramic radiograph showed reduced enamel thickness of all teeth, with a mild osteopenic appearance of the mandible [Figure 3]. The lateral cephalograph showed hypoplastic cervical vertebrae [Figure 4]. The anteroposterior (AP) and lateral radiographs of the thoracic-lumbar view revealed lumbar lordosis, osteopenic bones, platyspondyli of the multiple thoracic and lumbar vertebrae, and anterior wedging of the T1, T2, and L1 vertebrae. Flattening of the femoral heads and acetabular roof dysplasia, with secondary osteoarthritic changes, were noted [Figure 5].
|Figure 3: Panoramic radiograph showing an osteopenic mandible and reduced enamel thickness of all teeth|
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|Figure 5: Radiograph of an AP view of the thoracic-lumbar region, showing flattening of the femoral heads and acetabular roof dysplasia, with secondary osteoarthritic changes|
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Magnetic resonance imaging (MRI) of the thoracic spine revealed overall reduction in height of the lumbar vertebrae, with anterior vertebral height reduction of the thoracic and lumbar vertebral bodies. Pronounced anterior wedging was noted in the L1, L2, and L3 vertebral bodies [Figure 6]. The intervertebral disk had narrowed posteriorly, with relative preservation of the disk height anteriorly. Diffuse disk bulge was noted causing indentation of the thecal sac from the D9-D10 to the L4-L5 disk level [Figure 7]. Effacement of the anterior subarachnoid space and mild indentation of the spinal cord was noted at the D12 vertebral level [Figure 8]. The spinal cord ended at the normal level and was of normal signal intensity, and there was no tethering of the cord.
|Figure 6: MRI of the thoracic spine showing pronounced anterior wedging in the L1, L2 vertebral bodies|
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|Figure 7: MRI showing mild indentation of the spinal cord, noted at the D12 vertebral level|
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|Figure 8: MRI showing a diffuse disk bulge causing indentation of the thecal sac from the D9-D10 to the L4-L5 disk|
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Other investigations, such as, ultrasonography (USG) of the abdomen and cardiac evaluation were done. They did not reveal any abnormality.
Her blood investigation report was under normal limits, including the serum calcium. On consultation with a medical professional and on reviewing the literature it was found that the patient was suffering from Smith-McCort Variant syndrome, which is a part of the Dyggve-Melchior-Clausen syndrome More Details, where in patient usually present with mental retardation. In our case, the patient was intellectually normal.
Her dental treatment was carried out and the patient was referred to an orthopedician for further management of the skeletal dysplasia.
| Discussion|| |
The Smith-McCort syndrome More Details, which was first described by Smith and McCort in 1958, is a rare osteochondrodysplasia; specifically a spondyloepimetaphyseal dysplasia. It is a variant of the Dyggve-Melchior-Clausen syndrome (DMCS). DMCS is a rare autosomal recessive disorder produced by mutations in the Dymeclin (DYM) gene (mapped in the 18q12-21.1 chromosomal region). This gene is expressed in the brain, cartilage, and bone. SMS is also caused by mutations in the DYM, and thus is allelic to DMCS. The decreased level initially leads to abnormality of the cartilage and bone, but once the levels of functional protein drop below a certain threshold, the brain becomes affected, as in DMCS. , DMCS and SMS have identical skeletal abnormalities, but SMS lacks the intellectual disability.
The patients of SMS have a short trunk, dwarfism, a striking barrel-shaped chest, sternal protrusion, kyphoscoliosis, and various distal deformities, including genu valgum or varum. The most striking radiographical findings are lacy iliac crest apophysis, hip dysplasia, platyspondyly, double vertebral hump, and odontoid hypoplasia, with atlantoaxial instability. The diagnosis may be confirmed histologically, but no biochemical defect has been defined yet. 
In SEMD, disturbed growth can be recognized by abnormal radiographical findings within the epiphyses of long bones, the adjacent metaphyses, and the vertebral bodies. Patients may require orthopedic femoral osteotomy, total hip arthroplasty, early meniscectomy, realignment osteotomy, or posterior cervical spine fusion. 
Short limbs and a barrel-shaped chest, with normal mentality, in addition to double-humped vertebrae and an irregular lace-like appearance of the iliac crests are pathognomonic for DMC and SMC. 
Orodental findings are not often described with significance and include an everted lower lip, macroglossia, enamel hypoplasia, hypocalcification, prognathism, and decreased bone density.  Our case showed the characteristic skeletal and dental abnormalities of SMC, confirmed by radiographical findings.
Other subtypes of SEMD include subtype I, which is DMV, subtype III (X-linked with mental retardation), subtype IV (SEMD with joint laxity), subtype V (SEMD, strudwick type), subtype VI (SEMD, hypotrichosis), and subtype VII. 
Dyggve-Melchior-Clausen disease (DMC) - DMC is an autosomal recessive disorder, first described by Dyggve et al., in three children, who were offsprings of consanguineous parents. The syndrome is characterized by mental retardation and microcephaly. The radiological features, in addition to epiphyseal dysplasia and irregular metaphyses, include platyspondyly, with a central constriction of vertebral bodies that become more evident in late childhood. In adults the vertebral bodies become more rectangular. 
A pathognomonic radiological sign shows small iliac wings with a lacy appearance of the iliac crests, which is found to be caused by bone tissue deposited in a wavy pattern at the osteochondral junction.
SEMD with X-linked and mental deterioration - this distinct form of SEMD was described only once by Bieganski et al., in three boys, in a pattern consistent with X-linked recessive inheritance. The syndrome is characterized by its progressive nature. 
SEMD with joint laxity - a distinctive type of SEMD, associated with joint laxity and scoliosis (SEMDJL) was described by Beighton et al. Joint laxity was especially striking in the hands, with foreshortened fingernails and spatulate terminal phalanges. Hyperextensibility and instability of most joints with limited extension and supination of the elbows were reported. An oval face with prominent eyes, flat midface, long flat philtrum, and micrognathia were noted.
SEMD - Strudwick type - features include short stature, pectus carinatum, and scoliosis, with normal mentality, resembling Morquio disease. Delayed epiphyseal maturation is present at birth with distinctive mottling of the metaphyses (Dappling), a distinctive radiological feature resulting from alternating zones of osteosclerosis and osteopenia, which develop with age.
SEMD with hypotrichosis - congenital hypotrichosis, mild rhizomelic short stature, and genu varum are seen. The radiological features included mild metaphyseal flaring, irregular epiphyses, and pear-shaped vertebrae.
The clinical manifestations in this type include normal mentality, short stature with height below normal, joint pain and enlargement, with limited extension of both elbows and knees, wide costochondral junctions, flaring of the lower ribs, pectus carinatum, kyphosis, bowing of the tibia and fibula, and brachydactyly. Radiological examination revealed platyspondyly, with increased intervertebral disk spaces, short bowed long bones with defective epiphyseal mineralization, cupping of the metaphyses, flat acetabular roof, coxa vara and short ribs, with a narrow chest.
| Conclusion|| |
In summary, SEMD are genetically heterogeneous. Although all cases share generalized changes in the vertebrae, epiphyses and metaphyses of the long bones, additional associated clinical manifestations and pathognomonic radiological features were reported in different types. Different molecular defects were identified in some cases and not yet identifiable in others. With the great advances in molecular techniques it is necessary to identify the molecular basis for different types of SEMD for proper genetic counseling and prenataldiagnosis.
Our case showed peculiar orofacial features, including a diffuse osteopenic appearance of the mandible, changes in the cervical vertebra, enamel hypoplasia, and prognathism. From the point of view of an oral physician, it is one of the rare syndromes presenting with skeletal dysplasia and mimic some of the common bone diseases. Enamel hypoplasia is a part of this disorder. Although a rare syndrome, it is important to consider SMS in the differential diagnosis of bone dysplasia and refer the patient for necessary investigations and treatment, which can improve his/her quality of life.
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Conflicts of interest
There are no conflicts of interest.
| References|| |
Temtamy SA, Aglan MS, El-Gammal MA, Hosny LA, Ashour AM, El-Badry TH, et al
. Genetic heterogeneity in spondylo-epimetaphyseal dysplasias: A clinical and radiological study. Egypt J Hum Genet 2007;8:147-72.
Jones KL. Recognizable Patterns of Human Malformation. 6 th
ed. Philadelphia, PA: Elsevier, Saunders; 2006. p. 412.
El Ghouzzi V, Dagoneau N, Kinning E, Thauvin-Robinet C, Chemaitilly W, Prost-Squarcioni C, et al
. Mutations in a novel gene Dymeclin (FLJ20071) are responsible for Dyggve-Melchior-Clausensyndrome. Hum Mol Genet 2003;12:357-64.
Burns C, PowellBR, Hsia YE, Reinker K. Dyggve-Melchior-Clausen syndrome: Report of seven patients with the Smith-McCort variant and review of the literature. J Pediatr Orthop 2003;23:88-93.
Ehtesham N, Cantor RM, King LM, Reinker K, Powell BR, Shanske A, et al
. Evidence that Smith-McCort dysplasia and Dyggve-Melchior-Clausen dysplasia are allelic disorders that result from mutations in a gene on chromosome 18q12. Am J Hum Genet 2002;71:947-51.
Nakamura K, Kurokawa T, Nagano A, Nakamura S, Taniguchi K, Hamazaki M. Dyggve-Melchior-Clausen syndrome without mental retardation (Smith-McCort dysplasia): Morphological findings in the growth plate of the iliac crest. Am J Med Genet 1997;72:11-7.
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]