Dyssegmental dysplasia, Silverman-Handmaker type: prenatal ultrasound findings and molecular analysis

Dyssegmental dysplasia Rolland-Desbuquois type is caused by pathogenic variants in HSPG2 - a founder haplotype shared in five patients

Dyssegmental dysplasia (DD) is a severe skeletal dysplasia comprised of two subtypes: lethal Silverman-Handmaker type (DDSH) and nonlethal Rolland-Desbuquois type (DDRD). DDSH is caused by biallelic pathogenic variants in HSPG2 encoding perlecan, whereas the genetic cause of DDRD remains undetermined. Schwartz-Jampel syndrome (SJS) is also caused by biallelic pathogenic variants in HSPG2 and is an allelic disorder of DDSH. In SJS and DDSH, 44 and 8 pathogenic variants have been reported in HSPG2, respectively. Here, we report that five patients with DDRD carried four pathogenic variants in HSPG2: c.9970 G > A (p.G3324R), c.559 C > T (p.R187X), c7006 + 1 G > A, and c.11562 + 2 T > G. Two patients were homozygous for p.G3324R, and three patients were heterozygous for p.G3324R. Haplotype analysis revealed a founder haplotype spanning 85,973 bp shared in the five patients. SJS, DDRD, and DDSH are allelic disorders with pathogenic variants in HSPG2.

Proteoglycan Dysfunction: A Common Link Between Intervertebral Disc Degeneration and Skeletal Dysplasia

Proteoglycans through their sulfated glycosaminoglycans regulate cell-matrix signaling during tissue development, regeneration, and degeneration processes. Large extracellular proteoglycans such as aggrecan, versican, and perlecan are especially important for the structural integrity of the intervertebral disc and cartilage during development. In these tissues, proteoglycans are responsible for hydration, joint flexibility, and the absorption of mechanical loads. Loss or reduction of these molecules can lead to disc degeneration and skeletal dysplasia, evident from loss of disc height or defects in skeletal development respectively. In this review, we discuss the common proteoglycans found in the disc and cartilage and elaborate on various murine models and skeletal dysplasias in humans to highlight how their absence and/or aberrant expression causes accelerated disc degeneration and developmental defects.

Fetal Skeletal Dysplasias: Radiologic-Pathologic Classification of 72 Cases

ObjectiveThe aim of this study was to classify the fetal skeletal dysplasias (FSD) in a series of affected fetuses based on radio-pathologic criteria. Materials and methods: We gathered clinicopathologic data of 72 cases which were diagnosed among 5995 autopsies performed over a 8-year period. Results: The prevalence of FSD was 1.2:100 autopsies. The overall sex ratio (M:F) was 1.25. Gestational age was between 17 and 24 weeks in 60% of cases. The FSD were classified into 13 distinct pathologic groups. Four major groups were identified: (1) Osteogenesis imperfecta (21 cases, 29%); (2) FGFR3 chondrodysplasia (18 cases, 25%); (3) Ciliopathies (9 cases, 12%); and (4) Sulfation disorders (7 cases, 10%). Thanatophoric dysplasia type 1 and lethal osteogenesis imperfecta were the most common skeletal dysplasias. Conclusion: Our study demonstrates the usefulness of the radio-pathologic examination in the diagnosis and accurate classification of the FSD, thus enabling better targeting of genetic counseling.

Rare variant of HSPG2 is not involved in the development of adolescent idiopathic scoliosis: evidence from a large-scale replication study

BACKGROUND

Rare variants of HSPG2 have recently been reported to function as a potential contributor to the susceptibility of adolescent idiopathic scoliosis (AIS) in the Caucasians. A replication study in the different population is warranted to validate the role of HSPG2 in AIS. The aim of this study was to determine the association between HSPG2 and AIS in the Chinese patients and to further investigate its influence on the phenotype of the patients.

METHODS

SNVs p.Asn786Ser of HSPG2 was genotyped in 1752 patients and 1584 normal controls using multiple ligase detection reactions. The mRNA expression of HSPG2 in the paraspinal muscles was quantified for 90 patients and 26 controls. The The Student's t test was used to analyze the inter-group comparison of the HSPG2 expression. The relationship between the HSPG2 expression and the curve magnitude of the patients was analyzed by the Pearson correlation analysis.

RESULTS

No case of mutation in the reported SNV p.Asn786Ser of HSPG2 was found in our cohort. The mRNA expression of HSPG2 in patients was comparable with that in the controls (0.0016 ± 0.0013 vs. 0.0019 ± 0.0012, p = 0.29). 42 patients with curve magnitude > 60 degrees were assigned to the severe curve group. The other 58 patients were assigned to the moderate curve group. These two groups were found to have comparable HSPG2 expression (0.0015 ± 0.0011 vs. 0.0017 ± 0.0014, p = 0.57). And there was no remarkable correlation between the expression level of HSPG2 and the curve severity (r = 0.131, p = 0.71).

CONCLUSIONS

HSPG2 gene was not associated with the susceptibility or the phenotypes of AIS in the Chinese population. The whole HSPG2 gene can be sequenced in more AIS patients to identify potentially causative mutations.

Modular Proteoglycan Perlecan/HSPG2: Mutations, Phenotypes, and Functions

Heparan sulfate proteoglycan 2 (HSPG2) is an essential, highly conserved gene whose expression influences many developmental processes including the formation of the heart and brain. The gene is widely expressed throughout the musculoskeletal system including cartilage, bone marrow and skeletal muscle. The HSPG2 gene product, perlecan is a multifunctional proteoglycan that preserves the integrity of extracellular matrices, patrols tissue borders, and controls various signaling pathways affecting cellular phenotype. Given HSPG2's expression pattern and its role in so many fundamental processes, it is not surprising that relatively few gene mutations have been identified in viable organisms. Mutations to the perlecan gene are rare, with effects ranging from a relatively mild condition to a more severe and perinatally lethal form. This review will summarize the important studies characterizing mutations and variants of HSPG2 and discuss how these genomic modifications affect expression, function and phenotype. Additionally, this review will describe the clinical findings of reported HSPG2 mutations and their observed phenotypes. Finally, the evolutionary aspects that link gene integrity to function are discussed, including key findings from both in vivo animal studies and in vitro systems. We also hope to facilitate discussion about perlecan/HSPG2 and its role in normal physiology, to explain how mutation can lead to pathology, and to point out how this information can suggest pathways for future mechanistic studies.

Dyssegmental dysplasia, Silverman-Handmaker type: A challenging antenatal diagnosis in a dizygotic twin pregnancy

Background

Dyssegmental dysplasia Silverman‐Handmaker (DDSH; MIM 224410) type is an extremely rare skeletal dysplasia caused by functional null mutations in the perlecan gene. Less than forty cases are reported in the literature, of which only four were prenatally detected.

Methods

We report on a dizygotic twin pregnancy from consanguineous parents for which one of the twins presented prenatally with severe micromelia, limb bowing and scoliosis, and postnatally with clinical and radiological features compatible with a diagnosis of dyssegmental dysplasia. Molecular studies were undertaken to confirm the clinical diagnosis of DDSH.

Results

Molecular analysis results revealed a novel homozygous variant in the HSPG2 gene (MIM 142461), NM_005529.6(HSPG2):c.4029 + 1G>A, consistent with a diagnosis of DDSH.

Conclusion

To the best of our knowledge, the current report is only the seventh molecularly confirmed case of DDSH.