Unique dwarfing, spondylometaphyseal skeletal dysplasia, with joint laxity and dentinogenesis imperfecta

Hereditary dentin defects with systemic diseases

OBJECTIVE

This review aimed to summarize recent progress on syndromic dentin defects, promoting a better understanding of systemic diseases with dentin malformations, the molecules involved, and related mechanisms.

SUBJECTS AND METHODS

References on genetic diseases with dentin malformations were obtained from various sources, including PubMed, OMIM, NCBI, and other websites. The clinical phenotypes and genetic backgrounds of these diseases were then summarized, analyzed, and compared.

RESULTS

Over 10 systemic diseases, including osteogenesis imperfecta, hypophosphatemic rickets, vitamin D-dependent rickets, familial tumoral calcinosis, Ehlers-Danlos syndrome, Schimke immuno-osseous dysplasia, hypophosphatasia, Elsahy-Waters syndrome, Singleton-Merten syndrome, odontochondrodysplasia, and microcephalic osteodysplastic primordial dwarfism type II were examined. Most of these are bone disorders, and their pathogenic genes may regulate both dentin and bone development, involving extracellular matrix, cell differentiation, and metabolism of calcium, phosphorus, and vitamin D. The phenotypes of these syndromic dentin defects various with the involved genes, part of them are similar to dentinogenesis imperfecta or dentin dysplasia, while others only present one or two types of dentin abnormalities such as discoloration, irregular enlarged or obliterated pulp and canal, or root malformation.

CONCLUSION

Some specific dentin defects associated with systemic diseases may serve as important phenotypes for dentists to diagnose. Furthermore, mechanistic studies on syndromic dentin defects may provide valuable insights into isolated dentin defects and general dentin development or mineralization.

A Novel Heterozygous ACAN Variant in a Short Patient Born Small for Gestational Age with Recurrent Patellar Dislocation: A Case Report

ACAN variants can manifest as various clinical features, including short stature, advanced bone age (BA), and skeletal defects. Here, we report rare clinical manifestations of ACAN defects in a 9 year, 5 month-old girl born small for gestational age (SGA), who presented with short stature, and was initially diagnosed with idiopathic growth hormone deficiency. She displayed several dysmorphic features, including genu valgum, cubitus valgus, and recurrent patellar dislocations. She presented with progressive advancement of BA compared with chronological age. Whole exome sequencing confirmed the presence of a novel heterozygous nonsense variant, c.1968C>G, p.(Tyr656*), in ACAN. ACAN variants should be considered in short stature patients born SGA with joint problems, particularly those with recurrent patellar dislocation and genu valgum.

A Novel Mutation in the TRIP11 Gene: Diagnostic Approach from Relatively Common Skeletal Dysplasias to an Extremely Rare Odontochondrodysplasia

Odontochondrodysplasia (ODCD, OMIM #184260) is a rare, non-lethal skeletal dysplasia characterized by involvement of the spine and metaphyseal regions of the long bones, pulmonary hypoplasia, short stature, joint hypermobility, and dentinogenesis imperfecta. ODCD is inherited in an autosomal recessive fashion with an unknown frequency caused by mutations of the thyroid hormone receptor interactor 11 gene (TRIP11; OMIM *604505). The TRIP11 gene encodes the Golgi microtubule-associated protein 210 (GMAP-210), which is an indispensable protein for the function of the Golgi apparatus. Mutations in TRIP11 also cause achondrogenesis type 1A (ACG1A). Null mutations of TRIP11 lead to ACG1A, also known as a lethal skeletal dysplasia, while hypomorphic mutations cause ODCD. Here we report a male child diagnosed as ODCD with a novel compound heterozygous mutation who presented with skeletal changes, short stature, dentinogenesis imperfecta, and facial dysmorphism resembling achondroplasia and hypochondroplasia.

Description of four patients with TRIP11 variants expand the clinical spectrum of odontochondroplasia (ODCD) and demonstrate the existence of common variants

More than two decades since the first clinical and radiological description of odontochondroplasia (ODCD) was reported, biallelic loss of function variants in the Thyroid hormone receptor interactor 11 gene (TRIP11) were identified, the same gene implicated in the lethal disorder achondrogenesis (ACG1A). Here we report the clinical and radiological follow-up of four ODCD patients, including two siblings and an adult who interestingly has the mildest form observed to date. Four TRIP11 variants were detected, two previously unreported. Subsequently, we review the clinical and radiological findings of the 14 reported ODCD patients. The majority of ODCD patients are compound heterozygotes for TRIP11 variants, 12/14 have a null allele and a splice variant whilst one is homozygous for an in-frame splicing variant, with the splice variants resulting in residual GMAP activity and hypothesized to explain why they have ODCD and not ACG1A. However, adult patient 4 has two potentially null alleles and it remains unknown why she has very mild clinical features. The c.586C>T; p.(Gln196*) variant, previously shown by mRNA studies to result in p.Val105_Gln196del, is the most frequent variant, present in seven individuals from four families, three from different regions of the world, suggesting that it may be a variant hotspot. Another variant, c.2993_2994del; p.(Lys998Serfs*5), has been observed in two individuals with a possible common ancestor. In summary, although there are clinical and radiological characteristics common to all individuals, we demonstrate that the clinical spectrum of TRIP11-associated dysplasias is even more diverse than previously described and that common genetic variants may exist.

Pathogenic variants in the TRIP11 gene cause a skeletal dysplasia spectrum from odontochondrodysplasia to achondrogenesis 1A

The thyroid hormone receptor interactor 11 (TRIP11) gene encodes the Golgi microtubule-associated protein 210 (GMAP-210), a protein essential for the operation of the Golgi apparatus. It is known that null mutations in TRIP11 disrupt Golgi function and cause a lethal skeletal dysplasia known as achondrogenesis type 1A (ACG1A), however recently, hypomorphic mutations in that gene have been linked to odontochondrodysplasia (ODCD), a nonlethal skeletal dysplasia characterized by skeletal changes in the spine and in the metaphyseal regions, associated with dentinogenesis imperfecta. Here we present two patients reflecting the phenotypic spectrum related to different TRIP11 variants. The first is a female child with ODCD, for whom a homozygous in-frame splicing mutation in intron 9 of TRIP11 was identified. The mutation appears to lead to the expression of an alternative TRIP11 transcript, that may explain the less severe radiological alterations in ODCD. The second is a fetus with classical form of ACG1A, associated with typical molecular findings (frameshift) in exon 11 of TRIP11, both novel mutations. The two patients reported here represent the TRIP11 spectrum of skeletal dysplasia ranging from mild to lethal phenotypes, thereby enabling one to suggest a genotype-phenotype correlation in these diseases.

The Physiological Functions of the Golgin Vesicle Tethering Proteins

The golgins comprise a family of vesicle tethering proteins that act in a selective manner to tether transport vesicles at the Golgi apparatus. Tethering is followed by membrane fusion to complete the delivery of vesicle-bound cargo to the Golgi. Different golgins are localized to different regions of the Golgi, and their ability to selectively tether transport vesicles is important for the specificity of vesicle traffic in the secretory pathway. In recent years, our mechanistic understanding of golgin-mediated tethering has greatly improved. We are also beginning to appreciate how the loss of golgin function can impact upon physiological processes through the use of animal models and the study of human disease. These approaches have revealed that loss of a golgin causes tissue-restricted phenotypes, which can vary in severity and the cell types affected. In many cases, it is possible to attribute these phenotypes to a defect in vesicular traffic, although why certain tissues are sensitive to loss of a particular golgin is still, in most cases, unclear. Here, I will summarize recent progress in our understanding of golgins, focusing on the physiological roles of these proteins, as determined from animal models and the study of disease in humans. I will describe what these in vivo analyses have taught us, as well as highlight less understood aspects, and areas for future investigations.

Hypomorphic mutations of TRIP11 cause odontochondrodysplasia

Odontochondrodysplasia (ODCD) is an unresolved genetic disorder of skeletal and dental development. Here, we show that ODCD is caused by hypomorphic TRIP11 mutations, and we identify ODCD as the nonlethal counterpart to achondrogenesis 1A (ACG1A), the known null phenotype in humans. TRIP11 encodes Golgi-associated microtubule-binding protein 210 (GMAP-210), an essential tether protein of the Golgi apparatus that physically interacts with intraflagellar transport 20 (IFT20), a component of the ciliary intraflagellar transport complex B. This association and extraskeletal disease manifestations in ODCD point to a cilium-dependent pathogenesis. However, our functional studies in patient-derived primary cells clearly support a Golgi-based disease mechanism. In spite of reduced abundance, residual GMAP variants maintain partial Golgi integrity, normal global protein secretion, and subcellular distribution of IFT20 in ODCD. These functions are lost when GMAP-210 is completely abrogated in ACG1A. However, a similar defect in chondrocyte maturation is observed in both disorders, which produces a cellular achondrogenesis phenotype of different severity, ensuing from aberrant glycan processing and impaired extracellular matrix proteoglycan secretion by the Golgi apparatus.

Bi-allelic mutations of TRIP11 cause a spectrum of skeletal phenotypes whose severity is primarily based on impaired secretory trafficking and aberrant glycan processing.

Odontoblasts: Specialized hard-tissue-forming cells in the dentin-pulp complex

Odontoblasts are specialized cells that produce dentin and exhibit unique morphological characteristics; i.e., they extend cytoplasmic processes into dentinal tubules. While osteoblasts, which are typical hard-tissue-forming cells, are generated from mesenchymal stem cells during normal and pathological bone metabolism, the induction of odontoblasts only occurs once during tooth development, and odontoblasts survive throughout the lives of healthy teeth. During the differentiation of odontoblasts, signaling molecules from the inner enamel epithelium are considered necessary for the differentiation of odontoblast precursors, i.e., peripheral dental papilla cells. If odontoblasts are destroyed by severe external stimuli, such as deep caries, the differentiation of dental pulp stem cells into odontoblast-like cells is induced. Various bioactive molecules, such as non-collagenous proteins, might be involved in this process, although the precise mechanisms responsible for odontoblast differentiation have not been fully elucidated. Recently, our knowledge about the other functional activities of odontoblasts (apart from dentin formation) has increased. For example, it has been suggested that odontoblasts might act as nociceptive receptors, and surveillance cells that detect the invasion of exogenous pathogens. The regeneration of the dentin-pulp complex has recently gained much attention as a promising future treatment modality that could increase the longevity of pulpless teeth. Finally, congenital dentin anomalies, which are concerned with the disturbance of odontoblast functions, are summarized.

A second family with autosomal recessive spondylometaphyseal dysplasia and early death

We report on a consanguineous Lebanese family in which two sibs had pre- and post-natal growth retardation, developmental delay, large anterior fontanel, prominent forehead, low-set ears, depressed nasal bridge, short nose, anteverted nares, increased nasal width, prominent abdomen, and short limbs. Radiographs disclosed the presence of wormian bones, platyspondyly, decreased interpedicular distance at the lumbar vertebrae, square iliac bones, horizontal acetabula, trident acetabula, hypoplastic ischia, partial agenesis of the sacrum, ribs with cupped ends, short long bones with abnormal modeling, slight widening of the distal femoral metaphyses, and delayed epiphyseal ossification. Both sibs had a severe cardiomegaly and died at around 24 months from a heart failure. Differential diagnosis suggests that this is a second family presenting a newly described early lethal chondrodysplasia first reported by [Mégarbané et al. (2008); Am J Med Genet Part A 146A:2916-2919].

Transcriptional repression of the Dspp gene leads to dentinogenesis imperfecta phenotype in Col1a1-Trps1 transgenic mice

Dentinogenesis imperfecta (DGI) is a hereditary defect of dentin, a calcified tissue that is the most abundant component of teeth. Most commonly, DGI is manifested as a part of osteogenesis imperfecta (OI) or the phenotype is restricted to dental findings only. In the latter case, DGI is caused by mutations in the DSPP gene, which codes for dentin sialoprotein (DSP) and dentin phosphoprotein (DPP). Although these two proteins together constitute the majority of noncollagenous proteins of the dentin, little is known about their transcriptional regulation. Here we demonstrate that mice overexpressing the Trps1 transcription factor (Col1a1-Trps1 mice) in dentin-producing cells, odontoblasts, present with severe defects of dentin formation that resemble DGI. Combined micro-computed tomography (µCT) and histological analyses revealed tooth fragility due to severe hypomineralization of dentin and a diminished dentin layer with irregular mineralization in Col1a1-Trps1 mice. Biochemical analyses of noncollagenous dentin matrix proteins demonstrated decreased levels of both DSP and DPP proteins in Col1a1-Trps1 mice. On the molecular level, we demonstrated that sustained high levels of Trps1 in odontoblasts lead to dramatic decrease of Dspp expression as a result of direct inhibition of the Dspp promoter by Trps1. During tooth development Trps1 is highly expressed in preodontoblasts, but in mature odontoblasts secreting matrix its expression significantly decreases, which suggests a Trps1 role in odontoblast development. In these studies we identified Trps1 as a potent inhibitor of Dspp expression and the subsequent mineralization of dentin. Thus, we provide novel insights into mechanisms of transcriptional dysregulation that leads to DGI.

Majewski osteodysplastic primordial dwarfism type II (MOPD II): natural history and clinical findings

A description of the clinical features of Majewski osteodysplastic primordial dwarfism type II (MOPD II) is presented based on 58 affected individuals (27 from the literature and 31 previously unreported cases). The remarkable features of MOPD II are: severe intrauterine growth retardation (IUGR), severe postnatal growth retardation; relatively proportionate head size at birth which progresses to true and disproportionate microcephaly; progressive disproportion of the short stature secondary to shortening of the distal and middle segments of the limbs; a progressive bony dysplasia with metaphyseal changes in the limbs; epiphyseal delay; progressive loose-jointedness with occasional dislocation or subluxation of the knees, radial heads, and hips; unusual facial features including a prominent nose, eyes which appear prominent in infancy and early childhood, ears which are proportionate, mildly dysplastic and usually missing the lobule; a high squeaky voice; abnormally, small, and often dysplastic or missing dentition; a pleasant, outgoing, sociable personality; and autosomal recessive inheritance. Far-sightedness, scoliosis, unusual pigmentation, and truncal obesity often develop with time. Some individuals seem to have increased susceptibility to infections. A number of affected individuals have developed dilation of the CNS arteries variously described as aneurysms and Moya Moya disease. These vascular changes can be life threatening, even in early years because of rupture, CNS hemorrhage, and strokes. There is variability between affected individuals even within the same family.

Apparently new osteodysplastic and primordial short stature with severe microdontia, opalescent teeth, and rootless molars in two siblings

A Thai man and his sister affected with a newly recognized syndrome of proportionate primordial short stature are reported. The patients had severe intrauterine and postnatal growth retardation, prominent nose and nasal bridge, small pinnae, large sella turcica, areas of hypo- and hyperpigmentation of skin, dry and thin scalp hair, and long and straight clavicles. Ivory epiphyses and cone-shaped epiphyses of the hands were found when they were young, but most of them disappeared as they grew up. Scaphoid and trapezium had angular appearance. The second toes were unusually long. Distal symphalangism of toes and barchymesophalangy of fingers were noted. The findings that appear to distinguish this syndrome from the previously reported syndromes are long second toes, opalescent and rootless teeth, severe microdontia, severely hypoplastic alveolar process, and unerupted tooth. The mode of inheritance is suspected to be autosomal recessive.

A newly recognized syndrome of skeletal dysplasia with opalescent and rootless teeth

A Thai girl with skeletal dysplasia and dental anomalies was seen. Her anomalies consisted of disproportionately short stature, short neck, broad and depressed nasal bridge, broad chest in the anteroposterior dimension, kyphosis, widely spaced nipples, and protruded abdomen. Radiographic testing indicated that she had a large sella turcica, platyspondyly, hypoplastic acetabulum, and a small body of mandible. Both her deciduous and permanent teeth were equally opalescent, and most were rootless, with root development of the mandibular teeth more severely affected. Some maxillary roots were extremely short and tapered. Hypodontia was also observed. These findings represent a unique and hitherto undescribed syndrome of skeletal dysplasia with concomitant dental anomalies.

Novel COL1A1 mutation (G559C) [correction of G599C] associated with mild osteogenesis imperfecta and dentinogenesis imperfecta

A genotype-phenotype analysis of a three-generation family segregating for an autosomal-dominant osteogenesis imperfecta (OI) variant is reported here. The family was ascertained through the presentation of a proband concerned about discoloration of her teeth, found to be dentinogenesis imperfecta (DGI). Examination of 36 family members identified 15 individuals with DGI. Linkage studies were performed for genetic markers from candidate intervals known to contain genes responsible for DGI on chromosomes 4q, 7q, and 17q. Conclusive evidence for linkage of DGI was obtained to genetic markers on chromosome 17q21-q22 (DLX-3, Z(max) = 5.34, theta = 0.00). All DGI-affected family members shared a common haplotype, which was not present in individuals without DGI. Haplotype analysis sublocalized the gene to a 5-cM genetic interval that contained the collagen 1 alpha 1 (COL1A1) gene. More than 150 different COL1A1 gene mutations have been associated with various forms of OI, and five of these have been associated with DGI and type IV OI. After excluding these five mutations, mutational analysis was performed on the remaining exons including intron--exon boundaries, which resulted in identification of a Gly559Cys mutation in exon 32, present in all DGI-affected family members. Clinical features segregating with this G559C mutation included hyperextensible joints, joint pain and an increased propensity for bone fractures with moderate trauma. This is the first report of joint pain associated with a COL1A1 mutation and DGI. The mild skeletal features and reduced penetrance of the non-dental findings illustrate the importance of genetic evaluations for families with a history of DGI.

A rare form of spondylometaphyseal dysplasia-type A4

We present 2 cases of a previously apparently unreported spondylo-metaphyseal dysplasia comprising dwarfism, severe metaphyseal changes, ovoid vertebrae and mild platyspondyly with anterior tonguing of the vertebral bodies. The inheritance may be autosomal recessive.

[Odontochondrodysplasia]

BACKGROUND

Dentinogenesis imperfecta is exceptionally associated to chondrodysplasia. The aim of this work is to present four cases of such an association.

CASE REPORT

These four children (three boys; one girl) suffered from growth retardation, ligamentous hyperlaxity, scoliosis. Main features were present since the first months of life. Dentinogenesis imperfecta was more marked on the first teeth. On X-rays, all patients had short tubular bones, more pronounced at the level of the middle segment of their limbs, with irregular metaphyses. Cone-shaped epiphyses were present on the hands. Iliac wings were square-shaped and vertebral bodies had a posterior wedging.

CONCLUSION

These four cases, including two previously published as Goldblatt's syndrome, share the same findings as another case described by this author. We propose the name of odontochondrodysplasia for this apparently unfortuitous association: dentinogenesis imperfecta and chondrodysplasia.

The type II collagenopathies: a spectrum of chondrodysplasias

With the application of molecular techniques the aetiopathogenesis of skeletal dysplasias is gradually elucidated. Recent advances show that some bone dysplasias result from defects in the biosynthesis of type II (cartilage) collagen. Clinical entities caused by mutations in the COL2A1 gene coding for type II collagen comprise achondrogenesis II, hypochondrogenesis, spondyloepiphyseal dysplasia congenita, Kniest dysplasia, Stickler arthroophthalmopathy and mild dominant spondyloarthropathy. The mutations are expressed in the heterozygous state, and inheritance of type II collagenopathies is autosomal dominant. The wide range of clinical manifestations is not well understood but characterization of the basic defect may provide clues to establish specific genotype-phenotype correlations.

Type II collagen defect in two sibs with the Goldblatt syndrome, a chondrodysplasia with dentinogenesis imperfecta, and joint laxity

We report on a syndrome of spondylo-epimetaphyseal dysplasia, dentinogenesis imperfecta, and ligamentous hyperextensibility in two sibs born to nonconsanguineous parents. This chondrodysplasia was characterized by severe shortness of stature and an osteoporosis without fractures. Electron microscopic examination of the cartilage documented large vacuoles of dilated rough endoplasmic reticulum within the cytoplasm of chondrocytes. Gel electrophoresis of pepsin-soluble collagen extracted from cartilage demonstrated the presence of type II collagen chains with an abnormal mobility. Prolyl and lysyl hydroxylations were slightly increased. The abnormal molecules melted at a higher temperature than the normal ones. CNBr peptide mapping of type II collagen showed an altered electrophoretic migration of peptides CB 11, CB 8, and CB 10,5 whereas CB 9,7 looked normal. In addition, two small non-collagenous proteins isolated from cartilage were not found in an age-matched control individual but were detected in a normal newborn infant. The quantitation of proline-labelled collagen synthesized by dermal fibroblasts demonstrated a 50% reduction of total collagen. This decrease essentially affected the amount of extracellular type I collagen, which was secreted less efficiently than in control cells. Nevertheless, type I collagen chains behaved normally on 5% polyacrylamide gels. The reduced mRNA levels of alpha 1I and alpha 2I chains might reflect either a transcriptional defect or a decreased stability of mRNA transcripts. We suggest that the association of both pathological chondrocytes producing altered collagen type II and decreased synthesis of type I could be responsible for this peculiar phenotype. The overmodification of alpha 1II CNBr peptides is consistent with the presence of a single-base substitution in the COL2A1 gene. Whether there is a direct causal relationship between the type II collagen defect and the underexpression of type I collagen will require clarification.