Genotype-phenotype correlation and expansion of orodental anomalies in LTBP3-related disorders

Brachyolmia, dental anomalies and short stature (DASS): Phenotype and genotype analyses of Egyptian and Pakistani patients

Brachyolmia is a heterogeneous group of developmental disorders characterized by a short trunk, short stature, scoliosis, and generalized platyspondyly without significant deformities in the long bones. DASS (Dental Abnormalities and Short Stature), caused by alterations in the LTBP3 gene, was previously considered as a subtype of brachyolmia. The present study investigated three unrelated consanguineous families (A, B, C) with Brachyolmia and DASS from Egypt and Pakistan. In our Egyptian patients, we also observed hearing impairment. Exome sequencing was performed to determine the genetic causes of the diverse clinical conditions in the patients. Exome sequencing identified a novel homozygous splice acceptor site variant (LTBP3:c.3629-1G > T; p. ?) responsible for DASS phenotypes and a known homozygous missense variant (CABP2: c.590T > C; p.Ile197Thr) causing hearing impairment in the Egyptian patients. In addition, two previously reported homozygous frameshift variants (LTBP3:c.132delG; p.Pro45Argfs*25) and (LTBP3:c.2216delG; p.Gly739Alafs*7) were identified in Pakistani patients. This study emphasizes the vital role of LTBP3 in the axial skeleton and tooth morphogenesis and expands the mutational spectrum of LTBP3. We are reporting LTBP3 variants in seven patients of three families, majorly causing brachyolmia with dental and cardiac anomalies. Skeletal assessment documented short webbed neck, broad chest, evidences of mild long bones involvement, short distal phalanges, pes planus and osteopenic bone texture as additional associated findings expanding the clinical phenotype of DASS. The current study reveals that the hearing impairment phenotype in Egyptian patients of family A has a separate transmission mechanism independent of LTBP3.

Dental characteristics of patients with four different types of skeletal dysplasias

OBJECTIVE

Skeletal dysplasia (SD) comprises more than 450 separate disorders. We hypothesized that their dental features would be distinctive and investigated the tooth characteristics of four patients with different SDs.

MATERIAL AND METHODS

Four SD patients with molecularly confirmed diagnoses, Pt-1 acromicric dysplasia, Pt-2 hypophosphatasia and hypochondroplasia, Pt-3 cleidocranial dysplasia, and Pt-4 achondroplasia, were recruited. A tooth from each patient was evaluated for mineral density (micro-computerized tomography), surface roughness (surface profilometer), microhardness, mineral contents (energy-dispersive X-ray), and ultrastructure (scanning electron microscopy and histology), and compared with three tooth-type matched controls.

RESULTS

Pt-1 and Pt-3 had several unerupted teeth. Pt-2 had an intact-root-exfoliated tooth at 2 years old. The lingual surfaces of the patients' teeth were significantly smoother, while their buccal surfaces were rougher, than controls, except for Pt-1's buccal surface. The patients' teeth exhibited deep grooves around the enamel prisms and rough intertubular dentin. Pt-3 demonstrated a flat dentinoenamel junction and Pt-2 had an enlarged pulp, barely detectable cementum layer, and ill-defined cemento-dentinal junction. Reduced microhardnesses in enamel, dentin, and both layers were observed in Pt-3, Pt-4, and Pt-1, respectively. Pt-1 showed reduced Ca/P ratio in dentin, while both enamel and dentin of Pt-2 and Pt-3 showed reduced Ca/P ratio.

CONCLUSION

Each SD has distinctive dental characteristics with changes in surface roughness, ultrastructure, and mineral composition of dental hard tissues.

CLINICAL RELEVANCE

In this era of precision dentistry, identifying the specific potential dental problems for each patient with SD would help personalize dental management guidelines.

TGF-β and BMP Signaling Pathways in Skeletal Dysplasia with Short and Tall Stature

The transforming growth factor β (TGF-β) and bone morphogenetic protein (BMP) signaling pathways play a pivotal role in bone development and skeletal health. More than 30 different types of skeletal dysplasia are now known to be caused by pathogenic variants in genes that belong to the TGF-β superfamily and/or regulate TGF-β/BMP bioavailability. This review describes the latest advances in skeletal dysplasia that is due to impaired TGF-β/BMP signaling and results in short stature (acromelic dysplasia and cardiospondylocarpofacial syndrome) or tall stature (Marfan syndrome). We thoroughly describe the clinical features of the patients, the underlying genetic findings, and the pathomolecular mechanisms leading to disease, which have been investigated mainly using patient-derived skin fibroblasts and mouse models. Although no pharmacological treatment is yet available for skeletal dysplasia due to impaired TGF-β/BMP signaling, in recent years advances in the use of drugs targeting TGF-β have been made, and we also discuss these advances.

The biology of SCUBE

The SCUBE [Signal peptide-Complement C1r/C1s, Uegf, Bmp1 (CUB)-Epithelial growth factor domain-containing protein] family consists of three proteins in vertebrates, SCUBE1, 2 and 3, which are highly conserved in zebrafish, mice and humans. Each SCUBE gene encodes a polypeptide of approximately 1000 amino acids that is organized into five modular domains: (1) an N-terminal signal peptide sequence, (2) nine tandem epidermal growth factor (EGF)-like repeats, (3) a large spacer region, (4) three cysteine-rich (CR) motifs, and (5) a CUB domain at the C-terminus. Murine Scube genes are expressed individually or in combination during the development of various tissues, including those in the central nervous system and the axial skeleton. The cDNAs of human SCUBE orthologs were originally cloned from vascular endothelial cells, but SCUBE expression has also been found in platelets, mammary ductal epithelium and osteoblasts. Both soluble and membrane-associated SCUBEs have been shown to play important roles in physiology and pathology. For instance, upregulation of SCUBEs has been reported in acute myeloid leukemia, breast cancer and lung cancer. In addition, soluble SCUBE1 is released from activated platelets and can be used as a clinical biomarker for acute coronary syndrome and ischemic stroke. Soluble SCUBE2 enhances distal signaling by facilitating the secretion of dual-lipidated hedgehog from nearby ligand-producing cells in a paracrine manner. Interestingly, the spacer regions and CR motifs can increase or enable SCUBE binding to cell surfaces via electrostatic or glycan-lectin interactions. As such, membrane-associated SCUBEs can function as coreceptors that enhance the signaling activity of various serine/threonine kinase or tyrosine kinase receptors. For example, membrane-associated SCUBE3 functions as a coreceptor that promotes signaling in bone morphogenesis. In humans, SCUBE3 mutations are linked to abnormalities in growth and differentiation of both bones and teeth. In addition to studies on human SCUBE function, experimental results from genetically modified mouse models have yielded important insights in the field of systems biology. In this review, we highlight novel molecular discoveries and critical directions for future research on SCUBE proteins in the context of cancer, skeletal disease and cardiovascular disease.

Amelogenesis imperfecta: Next-generation sequencing sheds light on Witkop's classification

Amelogenesis imperfecta (AI) is a heterogeneous group of genetic rare diseases disrupting enamel development (Smith et al., Front Physiol, 2017a, 8, 333). The clinical enamel phenotypes can be described as hypoplastic, hypomineralized or hypomature and serve as a basis, together with the mode of inheritance, to Witkop's classification (Witkop, J Oral Pathol, 1988, 17, 547-553). AI can be described in isolation or associated with others symptoms in syndromes. Its occurrence was estimated to range from 1/700 to 1/14,000. More than 70 genes have currently been identified as causative. Objectives: We analyzed using next-generation sequencing (NGS) a heterogeneous cohort of AI patients in order to determine the molecular etiology of AI and to improve diagnosis and disease management. Methods: Individuals presenting with so called "isolated" or syndromic AI were enrolled and examined at the Reference Centre for Rare Oral and Dental Diseases (O-Rares) using D4/phenodent protocol (www.phenodent.org). Families gave written informed consents for both phenotyping and molecular analysis and diagnosis using a dedicated NGS panel named GenoDENT. This panel explores currently simultaneously 567 genes. The study is registered under NCT01746121 and NCT02397824 (https://clinicaltrials.gov/). Results: GenoDENT obtained a 60% diagnostic rate. We reported genetics results for 221 persons divided between 115 AI index cases and their 106 associated relatives from a total of 111 families. From this index cohort, 73% were diagnosed with non-syndromic amelogenesis imperfecta and 27% with syndromic amelogenesis imperfecta. Each individual was classified according to the AI phenotype. Type I hypoplastic AI represented 61 individuals (53%), Type II hypomature AI affected 31 individuals (27%), Type III hypomineralized AI was diagnosed in 18 individuals (16%) and Type IV hypoplastic-hypomature AI with taurodontism concerned 5 individuals (4%). We validated the genetic diagnosis, with class 4 (likely pathogenic) or class 5 (pathogenic) variants, for 81% of the cohort, and identified candidate variants (variant of uncertain significance or VUS) for 19% of index cases. Among the 151 sequenced variants, 47 are newly reported and classified as class 4 or 5. The most frequently discovered genotypes were associated with MMP20 and FAM83H for isolated AI. FAM20A and LTBP3 genes were the most frequent genes identified for syndromic AI. Patients negative to the panel were resolved with exome sequencing elucidating for example the gene involved ie ACP4 or digenic inheritance. Conclusion: NGS GenoDENT panel is a validated and cost-efficient technique offering new perspectives to understand underlying molecular mechanisms of AI. Discovering variants in genes involved in syndromic AI (CNNM4, WDR72, FAM20A … ) transformed patient overall care. Unravelling the genetic basis of AI sheds light on Witkop's AI classification.

Novel ITGB6 variants cause hypoplastic-hypomineralized amelogenesis imperfecta and taurodontism: characterization of tooth phenotype and review of literature

OBJECTIVES

To characterize phenotype and genotype of amelogenesis imperfecta (AI) in a Thai patient, and review of literature.

MATERIALS AND METHODS

Variants were identified using trio-exome and Sanger sequencing. The ITGB6 protein level in patient's gingival cells was measured. The patient's deciduous first molar was investigated for surface roughness, mineral density, microhardness, mineral composition, and ultrastructure.

RESULTS

The patient exhibited hypoplastic-hypomineralized AI, taurodontism, and periodontal inflammation. Exome sequencing identified the novel compound heterozygous ITGB6 mutation, a nonsense c.625 G > T, p.(Gly209*) inherited from mother and a splicing c.1661-3 C > G from father, indicating AI type IH. The ITGB6 level in patient cells was significantly reduced, compared with controls. Analyses of a patient's tooth showed a significant increase in roughness while mineral density of enamel and microhardness of enamel and dentin were significantly reduced. In dentin, carbon was significantly decreased while calcium, phosphorus, and oxygen levels were significantly increased. Severely collapsed enamel rods and a gap in dentinoenamel junction were observed. Of six affected families and eight ITGB6 variants that have been reported, our patient was the only one with taurodontism.

CONCLUSION

We report the hypoplasia/hypomineralization/taurodontism AI patient with disturbed tooth characteristics associated with the novel ITGB6 variants and reduced ITGB6 expression, expanding genotype, phenotype, and understanding of autosomal recessive AI.

Novel LTBP3 mutations associated with thoracic aortic aneurysms and dissections

BACKGROUND

Thoracic aortic aneurysm and dissection (TAAD) is a hidden-onset but life-threatening disorder with high clinical variability and genetic heterogeneity. In recent years, an increasing number of genes have been identified to be related to TAAD. However, some genes remain uncertain because of limited case reports and/or functional studies. LTBP3 was such an ambiguous gene that was previously known for dental and skeletal dysplasia and then noted to be associated with TAAD. More research on individuals or families harboring variants in this gene would be helpful to obtain full knowledge of the disease and clarify its association with TAAD.

METHODS

A total of 266 TAAD probands with no causative mutations in known genes had been performed wholeexome sequencing (WES) to identify potentially pathogenic variants. In this study, rare LTBP3 variants were the focus of analysis.

RESULTS

Two compound heterozygous mutations, c.625dup (p.Leu209fs) and c.1965del (p.Arg656fs), in LTBP3 were identified in a TAAD patient along with short stature and dental problems, which was the first TAAD case with biallelic LTBP3 null mutations in an Asian population. Additionally, several rare heterozygous LTBP3 variants were also detected in other sporadic TAAD patients.

CONCLUSION

The identification of LTBP3 mutations in TAAD patients in our study provided more clinical evidence to support its association with TAAD, which broadens the gene spectrum of LTBP3. LTBP3 should be considered to be incorporated into the routine genetic analysis of heritable aortopathy, which might help to fully understand its phenotypic spectrum and improve the diagnostic rate of TAAD.

Reduced ELANE and SLPI expression compromises dental pulp cell activity

Background

Patients with ELANE variants and severe congenital neutropenia (SCN) commonly develop oral complications. Whether they are caused only by low neutrophil count or the combination of neutropenia and aberrant dental cells is unknown.

Methods

Genetic variant was identified with exome sequencing. Dental pulp cells isolated from the SCN patient with an ELANE mutation were investigated for gene expression, enzyme activity, proliferation, colony formation, wound healing, apoptosis, ROS, attachment, spreading and response to lipopolysaccharide.

Results

ELANE cells had diminished expression of ELANE and SLPI and reduced neutrophil elastase activity. Moreover, ELANE cells exhibited impaired proliferation, colony forming, migration, attachment and spreading; and significantly increased ROS formation and apoptosis, corresponding with increased Cyclin D1 and MMP2 levels. The intrinsic levels of TGF‐β1 and TNF‐α were significantly increased; however, IL‐6, IL‐8 and NF‐kB1 were significantly decreased in ELANE cells compared with those in controls. After exposure to lipopolysaccharide, ELANE cells grew larger, progressed to more advanced cell spreading stages and showed significantly increased SLPI, TNF‐α and NF‐kB1 and tremendously increased IL‐6 and IL‐8 expression, compared with controls.

Conclusion

This study, for the first time, suggests that in addition to neutropenia, the aberrant levels and functions of ELANE, SLPI and their downstream molecules in pulp cells play an important role in oral complications in SCN patients. In addition, pulp cells with diminished neutrophil elastase and SLPI are highly responsive to inflammation.

A Rare Case of Brachyolmia with Amelogenesis Imperfecta Caused by a New Pathogenic Splicing Variant in LTBP3

In recent years, a rare form of autosomal recessive brachyolmia associated with amelogenesis imperfecta (AI) has been described as a novel nosologic entity. This disorder is characterized by skeletal dysplasia (e.g., platyspondyly, short trunk, scoliosis, broad ilia, elongated femoral necks with coxa valga) and severe enamel and dental anomalies. Pathogenic variants in the latent transforming growth factor-β binding protein 3 (LTBP3) gene have been found implicated in the pathogenesis of this disorder. So far, biallelic pathogenic LTBP3 variants have been identified in less than 10 families. We here report a young boy born from consanguineous parents with a complex phenotype including skeletal dysplasia associated with aortic stenosis, hypertrophic cardiomyopathy, hypodontia and amelogenesis imperfecta caused by a previously unreported homozygous LTBP3 splice site variant. We also compare the genotypes and phenotypes of patients reported to date. This work provides further evidence that brachyolmia with amelogenesis imperfecta is a distinct nosologic entity and that variations in LTBP3 are involved in its pathogenesis.

Clinical Genetic Risk Variants Inform a Functional Protein Interaction Network for Tetralogy of Fallot

BACKGROUND

Tetralogy of Fallot (TOF)-the most common cyanotic heart defect in newborns-has evidence of multiple genetic contributing factors. Identifying variants that are clinically relevant is essential to understand patient-specific disease susceptibility and outcomes and could contribute to delineating pathomechanisms.

METHODS

Using a clinically driven strategy, we reanalyzed exome sequencing data from 811 probands with TOF, to identify rare loss-of-function and other likely pathogenic variants in genes associated with congenital heart disease.

RESULTS

We confirmed a major contribution of likely pathogenic variants in FLT4 (VEGFR3 [vascular endothelial growth factor receptor 3]; n=14) and NOTCH1 (n=10) and identified 1 to 3 variants in each of 21 other genes, including ATRX, DLL4, EP300, GATA6, JAG1, NF1, PIK3CA, RAF1, RASA1, SMAD2, and TBX1. In addition, multiple loss-of-function variants provided support for 3 emerging congenital heart disease/TOF candidate genes: KDR (n=4), IQGAP1 (n=3), and GDF1 (n=8). In total, these variants were identified in 63 probands (7.8%). Using the 26 composite genes in a STRING protein interaction enrichment analysis revealed a biologically relevant network (P=3.3×10-16), with VEGFR2 (vascular endothelial growth factor receptor 2; KDR) and NOTCH1 (neurogenic locus notch homolog protein 1) representing central nodes. Variants associated with arrhythmias/sudden death and heart failure indicated factors that could influence long-term outcomes.

CONCLUSIONS

The results are relevant to precision medicine for TOF. They suggest considerable clinical yield from genome-wide sequencing, with further evidence for KDR (VEGFR2) as a congenital heart disease/TOF gene and for VEGF (vascular endothelial growth factor) and Notch signaling as mechanisms in human disease. Harnessing the genetic heterogeneity of single gene defects could inform etiopathogenesis and help prioritize novel candidate genes for TOF.

Expanding the genotypic spectrum of PYCR2 and a common ancestry in Thai patients with hypomyelinating leukodystrophy 10

PYCR2 pathogenic variants lead to an autosomal recessive hypomyelinating leukodystrophy 10 (HLD10), characterized by global developmental delay, microcephaly, facial dysmorphism, movement disorder, and hypomyelination. This study identified the first two unrelated Thai patients with HLD10. Patient 1 harbored the novel compound heterozygous variants, c.257T>G (p.Val86Gly) and c.400G>A (p.Val134Met), whereas patient 2 possessed the homozygous variant, c.400G>A (p.Val134Met), in PYCR2. Haplotype analysis revealed that the two families' members shared a 2.3 Mb region covering the c.400G>A variant, indicating a common ancestry. The variant was estimated to age 1450 years ago. Since the c.400G>A was detected in three out of four mutant alleles and with a common ancestry, this variant might be common in Thai patients. We also reviewed the phenotype and genotype of all 35 previously reported PYCR2 patients and found that majorities of cases were homozygous with a consanguineous family history, except patient 1 and another reported case who were compound heterozygous. All patients had microcephaly and developmental delay. Hypotonia and peripheral spasticity were common. Hypomyelination or delayed myelination was a typical radiographic feature. Here, we report the first two Thai patients with HLD10 with the novel PYCR2 variants expanding the genotypic spectrum and suggest that the c.400G>A might be a common mutation in Thai patients.

A Review of Three Chinese Cases of Acromicric/Geleophysic Dysplasia with FBN1 Mutations

Objective

This study aims to explore the clinical features and molecular diagnosis of FBN1-related acromelic dysplasia in Chinese patients.

Methods

The clinical and genetic features of three FBN1-related acromicric dysplasia (AD)/geleophysic dysplasia (GD) Chinese patients from two families were reviewed, and comprehensive medical evaluations were performed. Targeted next-generation sequencing was used to detect genetic mutations associated with short statures, including FBN1. Sanger sequencing was used to determine the de novo mutation origin.

Results

Patient 1 presented with short stature, short and stubby hands and feet, mild facial dysmorphism, hepatomegaly, delayed bone age and beak-like femoral heads. Patient 2 and this patient’s father merely presented with short stature, wide and short hands, and beak-like femoral heads. One novel mutation, c.5272G>T(p.D1758Y), and one known mutation, c.5183C>T(p.A1728V), were identified in these patients.

Conclusion

The clinical features varied among these patients. The variant c.5272G>T(p.D1758Y) is a novel mutation.

Phenotypic features of dentinogenesis imperfecta associated with osteogenesis imperfecta and COL1A2 mutations

OBJECTIVE

Dentinogenesis imperfecta (DI) requires dental treatment. This study investigated the characteristics of DI teeth associated with osteogenesis imperfecta (OI) and COL1A2 mutations.

STUDY DESIGN

Whole exome and Sanger sequencing were performed. Three primary teeth (called "OIDI teeth") obtained from 3 unrelated COL1A2 patients were investigated and compared with 9 control teeth from age-matched healthy individuals using colorimetry, micro-computed tomography, Knoop microhardness, energy dispersive X-ray spectroscopy, scanning electron microscopy, and histology.

RESULTS

All patients were identified with heterozygous glycine substitutions in COL1A2. The COL1A2 mutations, c.1531G>T and c.2027G>T, were de novo, whereas c.3106G>C was inherited. OIDI1, 2, and 3 teeth had a substantial decrease in dentin microhardness and lightness. OIDI2 enamel microhardness was significantly reduced, whereas OIDI1 and 3 had enamel microhardness comparable to that of control individuals. The OIDI1 pulp cavity was large; OIDI2 was narrow; and OIDI3 was obliterated. OIDI1 and 3 had significantly higher carbon levels than those in control individuals. Numerous ectopic calcified masses, sparse and obstructed dentinal tubules, dentin holes, and collagen disorientation were observed.

CONCLUSIONS

OIDI teeth had reduced lightness and variable pulp morphology. Weak dentin, mineral disproportion, and abnormal ultrastructure could contribute to the brittleness of OIDI teeth and adhesive restoration failure. Here, we expand the phenotypic spectrum of COL1A2 mutations and raise awareness among dentists seeing patients with OI.

Age-related dental phenotypes and tooth characteristics of FAM83H-associated hypocalcified amelogenesis imperfecta

OBJECTIVES

Autosomal-dominant hypocalcified amelogenesis imperfecta (ADHCAI) shows phenotypic heterogeneity. Our aim was to characterise the ADHCAI phenotypes, tooth properties and genotypes.

METHODS

Three unrelated ADHCAI probands and seven additional affected members of the three families were recruited. Mutations were identified by exome and Sanger sequencing, and haplotypes by SNP array. Tooth colour, roughness, density, nanohardness, minerals and ultrastructure were investigated.

RESULTS

Ten participants were heterozygous for the FAM83H mutation c.1387C>T (p.Gln463*). All shared a 3.43 Mbp region on chromosome 8q24.3 encompassing the FAM83H variant, indicating a common ancestry. The c.1387C>T was estimated to be 23.8 generations or 600 years. The FAM83H enamel had higher roughness and lower lightness, density, nanohardness, and calcium and phosphorus levels than controls. Blunted enamel rods, wide interrod spaces and disorganised dentinoenamel junctions were observed. Evaluating the patients with the same mutation and reviewing others with different mutations in FAM83H revealed that the FAM83H heterogeneous phenotypes are age-influenced. Tooth colour and surface texture change with ageing.

CONCLUSIONS

FAM83H enamel demonstrated decreased lightness, density, hardness, calcium, phosphorus and defective ultrastructure. We have identified that the phenotypic variation in FAM83H-associated ADHCAI is age-related. Awareness of the correlation between age and clinical features of FAM83H-ADHCAI can help dentists make an accurate diagnosis.

SCUBE3 loss-of-function causes a recognizable recessive developmental disorder due to defective bone morphogenetic protein signaling

Signal peptide-CUB-EGF domain-containing protein 3 (SCUBE3) is a member of a small family of multifunctional cell surface-anchored glycoproteins functioning as co-receptors for a variety of growth factors. Here we report that bi-allelic inactivating variants in SCUBE3 have pleiotropic consequences on development and cause a previously unrecognized syndromic disorder. Eighteen affected individuals from nine unrelated families showed a consistent phenotype characterized by reduced growth, skeletal features, distinctive craniofacial appearance, and dental anomalies. In vitro functional validation studies demonstrated a variable impact of disease-causing variants on transcript processing, protein secretion and function, and their dysregulating effect on bone morphogenetic protein (BMP) signaling. We show that SCUBE3 acts as a BMP2/BMP4 co-receptor, recruits the BMP receptor complexes into raft microdomains, and positively modulates signaling possibly by augmenting the specific interactions between BMPs and BMP type I receptors. Scube3-/- mice showed craniofacial and dental defects, reduced body size, and defective endochondral bone growth due to impaired BMP-mediated chondrogenesis and osteogenesis, recapitulating the human disorder. Our findings identify a human disease caused by defective function of a member of the SCUBE family, and link SCUBE3 to processes controlling growth, morphogenesis, and bone and teeth development through modulation of BMP signaling.

Expanding phenotypic and mutational spectra of mitochondrial HMG-CoA synthase deficiency

Mitochondrial 3-hydroxy-3 methylglutaryl-CoA synthase-2 deficiency (HMGCS2D) is a rare autosomal recessive inborn error of hepatic ketogenesis, caused by mutations in HMGCS2. As its clinical and laboratory manifestations resemble many other metabolic disorders, HMGCS2D definite diagnosis presents a challenge, frequently requiring molecular tests. Only 26 patients with HMGCS2 mutations have been previously described, and this study reports the first two unrelated Thai patients, a 9-month-old male and an 8-month-old female, with HMGCS2D. During acute episodes, steatorrhea and dyslipidemia occurred, both previously unreported. Increased serum levels of triglycerides, very low density lipoproteins (VLDL), and low density lipoproteins (LDL), along with a decreased serum level of HDL were found. Both patients had hypophosphatemic encephalopathy, and the female had metabolic acidosis without hypoglycemia. Trio whole-exome sequencing (WES) revealed that the male harbored two HMGCS2 mutations, a novel c.1480C>T (p.Arg494*) and a previously reported c.1502G>C (p.Arg501Pro), while the female was compound heterozygous for the c.1502G>C (p.Arg501Pro) and a previously reported mutation, c.520T>C (p.Phe174Leu). Interestingly, c.1502G>C (p.Arg501Pro) was not only found in both of our patients but also detected heterozygously in 9 out of 1081 unrelated individuals (allele frequency of 9/2162; 0.42%) in our in-house Thai exome database. Discovery of this common mutation suggests there could be about 14 babies with HMGCS2D within 800,000 newborns in Thailand annually. Therefore, awareness of HMGCS2D among medical personnel in Thailand should be raised.

Acromelic dysplasias: how rare musculoskeletal disorders reveal biological functions of extracellular matrix proteins

Acromelic dysplasias are a group of rare musculoskeletal disorders that collectively present with short stature, pseudomuscular build, stiff joints, and tight skin. Acromelic dysplasias are caused by mutations in genes (FBN1, ADAMTSL2, ADAMTS10, ADAMTS17, LTBP2, and LTBP3) that encode secreted extracellular matrix proteins, and in SMAD4, an intracellular coregulator of transforming growth factor-β (TGF-β) signaling. The shared musculoskeletal presentations in acromelic dysplasias suggest that these proteins cooperate in a biological pathway, but also fulfill distinct roles in specific tissues that are affected in individual disorders of the acromelic dysplasia group. In addition, most of the affected proteins directly interact with fibrillin microfibrils in the extracellular matrix and have been linked to the regulation of TGF-β signaling. Together with recently developed knockout mouse models targeting the affected genes, novel insights into molecular mechanisms of how these proteins regulate musculoskeletal development and homeostasis have emerged. Here, we summarize the current knowledge highlighting pathogenic mechanisms of the different disorders that compose acromelic dysplasias and provide an overview of the emerging biological roles of the individual proteins that are compromised. Finally, we develop a conceptual model of how these proteins may interact and form an "acromelic dysplasia complex" on fibrillin microfibrils in connective tissues of the musculoskeletal system.

Chondrodysplasias and Aneurysmal Thoracic Aortopathy: An Emerging Tale of Molecular Intersection

Although at first glance chondrodysplasia and aneurysmal thoracic aortopathy seem oddly dissimilar, recent lines of evidences indicate that they share molecular similarities. Chondrodysplasias are a group of skeletal disorders characterized by genetic defects in hyaline cartilage. Aneurysmal thoracic aortopathy is the pathological enlargement of the thoracic aorta due to wall weakness, along with its ensuing life-threatening complications (i.e., aortic dissection and/or rupture). Extracellular matrix dysregulation, abnormal TGF-β signaling, and, to a more limited extent, endoplasmic reticulum stress emerge as common disease processes. In this review we provide a comprehensive overview of the genetic and pathomechanistic overlap as well as of how these commonalities can guide treatment strategies for both disease entities.

Bi-allelic loss-of-function novel variants in LTBP3-related skeletal dysplasia: Report of first patient from India

Dental anomalies and short stature (DASS) has been recently identified as a distinct entity, associated with bi-allelic hypomorphic variants in LTBP3 gene. Only 20 individuals from nine families have been previously reported, with a consistent phenotype of short stature, brachyolmia, and amelogenesis imperfecta. We report the first case from India, with novel radiographic and molecular findings in LTBP3 gene, thereby expanding the phenotypic spectrum of DASS.

Acromicric dysplasia with stiff skin syndrome-like severe cutaneous presentation in an 8-year-old boy with a missense FBN1 mutation: Case report and literature review

Background

Acromicric dysplasia is a rare heritable short‐stature syndrome with joint stiffness and varying degrees of cutaneous hardness. Stiff skin syndrome is a rare connective tissue disorder characterized by diffusely thick and hard skin from the time of birth. Heterozygous point mutations in the FBN1 have been proposed as the predominant cause of both diseases.

Methods

By performing skin biopsy, X‐ray imaging, electrocardiography, as well as whole‐genome sequencing and Sanger sequencing, we diagnosed an 8‐year‐old Chinese boy as acromicric dysplasia with severe skin stiffness caused by a heterogeneous mutation in the FBN1.

Results

The patient presented with skin tightness, wrist and ankle stiffness, short stature and limbs, several deformed joints in the extremities, cone‐shaped epiphyses, and distinct facial features. He also had a patent foramen ovale and frequent respiratory infections. Skin biopsy showed thickened dermis and excessive collagen aggregation. Alcian blue staining indicated dermal mucopolysaccharide deposition. Mutation analysis revealed a heterozygous missense mutation, c.5243G>A (p.Cys1748Tyr), in exon 42 of the FBN1.

Conclusion

This is a report about acromicric dysplasia with stiff skin syndrome‐like severe cutaneous presentation caused by a single hotspot mutation, further revealing the gene pleiotropy of FBN1.

A family with homozygous and heterozygous p.Gly337Ser mutations in COL1A2

Osteogenesis imperfecta (OI) is commonly caused by monoallelic mutations in COL1A1 or COL1A2. Biallelic mutations are extremely rare. Only five previous reports have identified seven OI patients with homozygous mutations in COL1A2. OI is a genetically and phenotypically heterogeneous disorder which challenges an establishment of genotype-phenotype correlation. Notably, more than thirty patients with OI possess the heterozygous mutation, p.Gly337Ser, in COL1A2. Their clinical severity ranges from mild OI type I to severe types III and IV. Here, we report a 17-year-old Thai female with recurrent bone fractures, short stature, blue sclerae, triangular face, missing teeth, dentinogenesis imperfecta (DI), skeletal deformities, and scoliosis. She was diagnosed with OI type III. Her parents were second-cousin-once-removed. The father was a professional Thai boxer. Both had normal bone mineral density, no history of bone fractures, and only teeth problems. They were diagnosed with DI without OI. Whole exome sequencing identified that the proband harbored the homozygous mutation, c.1009G > A (p.Gly337Ser), in exon 19 of COL1A2 while her parents were heterozygous for this mutation. This study reports the eighth child with OI and the homozygous mutation in COL1A2; and the first two individuals with the heterozygous p.Gly337Ser mutation in COL1A2 causing an isolated DI without OI.