Stüve-Wiedemann syndrome (SWS) is characterised by bowing of the lower limbs, respiratory distress and hyperthermia that are often responsible for early death. Survivors develop progressive scoliosis ...and spontaneous fractures. We previously identified
mutations in most SWS cases, but absence of
pathogenic changes in five patients led us to perform exome sequencing and to identify homozygosity for a
mutation in one case p.Ser205Tyrfs*13. The follow-up of this case supported a final diagnosis of osteogenesis imperfecta (OI), based on vertebral collapses and blue sclerae.
This prompted us to screen
in 25 OI patients with no known mutations.We identified a homozygous deleterious variant in
in two affected sibs with typical OI p.His127Arg. Another homozygous variant, p.Asp231Gly, also classed as deleterious, was detected in a patient with type III OI of consanguineous parents using homozygosity mapping and exome sequencing.FAM46A is a member of the superfamily of nucleotidyltransferase fold proteins but its exact function is presently unknown. Nevertheless, there are lines of evidence pointing to a relevant role of FAM46A in bone development. By RT-PCR analysis, we detected specific expression of
in human osteoblasts andinterestingly, a nonsense mutation in
has been recently identified in an ENU-derived (
-ethyl-
-nitrosourea) mouse model characterised by decreased body length, limb, rib, pelvis, and skull deformities and reduced cortical thickness in long bones.
We conclude that
mutations are responsible for a severe form of OI with congenital bowing of the lower limbs and suggest screening this gene in unexplained OI forms.
To describe our experience with a large cohort (411 patients from 288 families) of various forms of skeletal dysplasia who were molecularly characterized.
Detailed phenotyping and next-generation ...sequencing (panel and exome).
Our analysis revealed 224 pathogenic/likely pathogenic variants (54 (24%) of which are novel) in 123 genes with established or tentative links to skeletal dysplasia. In addition, we propose 5 genes as candidate disease genes with suggestive biological links (WNT3A, SUCO, RIN1, DIP2C, and PAN2). Phenotypically, we note that our cohort spans 36 established phenotypic categories by the International Skeletal Dysplasia Nosology, as well as 18 novel skeletal dysplasia phenotypes that could not be classified under these categories, e.g., the novel C3orf17-related skeletal dysplasia. We also describe novel phenotypic aspects of well-known disease genes, e.g., PGAP3-related Toriello–Carey syndrome–like phenotype. We note a strong founder effect for many genes in our cohort, which allowed us to calculate a minimum disease burden for the autosomal recessive forms of skeletal dysplasia in our population (7.16E-04), which is much higher than the global average.
By expanding the phenotypic, allelic, and locus heterogeneity of skeletal dysplasia in humans, we hope our study will improve the diagnostic rate of patients with these conditions.
Back pain is a common condition with a high social impact and represents a global health burden. Intervertebral disc disease (IVDD) is one of the major causes of back pain; no therapeutics are ...currently available to reverse this disease. The impact of bone mineral density (BMD) on IVDD has been controversial, with some studies suggesting osteoporosis as causative for IVDD and others suggesting it as protective for IVDD. Functional studies to evaluate the influence of genetic components of BMD in IVDD could highlight opportunities for drug development and repurposing. By taking a holistic 3D approach, we established an aging zebrafish model for spontaneous IVDD. Increased BMD in aging, detected by automated computational analysis, is caused by bone deformities at the endplates. However, aged zebrafish spines showed changes in bone morphology, microstructure, mineral heterogeneity, and increased fragility that resembled osteoporosis. Elements of the discs recapitulated IVDD symptoms found in humans: the intervertebral ligament (equivalent to the annulus fibrosus) showed disorganized collagen fibers and herniation, while the disc center (nucleus pulposus equivalent) showed dehydration and cellular abnormalities. We manipulated BMD in young zebrafish by mutating sp7 and cathepsin K, leading to low and high BMD, respectively. Remarkably, we detected IVDD in both groups, demonstrating that low BMD does not protect against IVDD, and we found a strong correlation between high BMD and IVDD. Deep learning was applied to high-resolution synchrotron µCT image data to analyze osteocyte 3D lacunar distribution and morphology, revealing a role of sp7 in controlling the osteocyte lacunar 3D profile. Our findings suggest potential avenues through which bone quality can be targeted to identify beneficial therapeutics for IVDD.
Spondyloepimetaphyseal dysplasia-Shohat type (SEMDSH) is an ultra-rare type of skeletal dysplasia. Only nine patients from six families have been reported and genetically confirmed to have biallelic ...pathogenic variants in the DDRGK1 gene. We present a patient with typical clinical features of the disorder, including disproportionate short-limbed short stature, short neck, short chest with pectus carinatum, exaggerated lumbar lordosis and marked genu vara. Our patient further showed microcephaly, unilateral choanal atresia and antenatal fractures, features that were not reported before in association with this disorder. Radiological changes over time were presented, including delayed epiphyseal ossification, broad metaphysis with marked irregularities that progressed with age, fibular overgrowth, and characteristic spine changes with early platyspondyly and squaring of vertebral bodies at a later age. Exome sequencing revealed a homozygous pathogenic donor splice site variant in the DDRGK1 gene (NM_023935.3:c.408+1G > A). This mutation was also previously identified in patients from Iraqi descent. Our study expands the phenotypic spectrum of SEMDSH, emphasizes the radiological changes with age in SEMDSH patients, and recommends prolonged follow-up for these cases better to delineate the phenotype and surveillance for possible complications.
Osteogenesis imperfecta (OI) types VII, VIII and IX, caused by recessive mutations in cartilage-associated protein (
), prolyl-3-hydroxylase 1 (
) and cyclophilin B (
), respectively, are ...characterized by the synthesis of overmodified collagen. The genes encode for the components of the endoplasmic reticulum (ER) complex responsible for the 3-hydroxylation of specific proline residues in type I collagen. Our study dissects the effects of mutations in the proteins of the complex on cellular homeostasis, using primary fibroblasts from seven recessive OI patients. In all cell lines, the intracellular retention of overmodified type I collagen molecules causes ER enlargement associated with the presence of protein aggregates, activation of the PERK branch of the unfolded protein response and apoptotic death. The administration of 4-phenylbutyrate (4-PBA) alleviates cellular stress by restoring ER cisternae size, and normalizing the phosphorylated PERK (p-PERK):PERK ratio and the expression of apoptotic marker. The drug also has a stimulatory effect on autophagy. We proved that the rescue of cellular homeostasis following 4-PBA treatment is associated with its chaperone activity, since it increases protein secretion, restoring ER proteostasis and reducing PERK activation and cell survival also in the presence of pharmacological inhibition of autophagy. Our results provide a novel insight into the mechanism of 4-PBA action and demonstrate that intracellular stress in recessive OI can be alleviated by 4-PBA therapy, similarly to what we recently reported for dominant OI, thus allowing a common target for OI forms characterized by overmodified collagen.This article has an associated First Person interview with the first author of the paper.
Biallelic variants in CHST3 gene result in congenital dislocation of large joints, club feet, short stature, rhizomelia, kypho‐scoliosis, platyspondyly, epiphyseal dysplasia, flared metaphysis, in ...addition to minor cardiac lesions and hearing loss. Herein, we describe 14 new patients from 11 unrelated Egyptian families with CHST3‐related skeletal dysplasia. All patients had spondyloepiphyseal changes that were progressive with age in addition to bifid distal ends of humeri which can be considered a diagnostic key in patients with CHST3 variants. They also shared peculiar facies with broad forehead, broad nasal tip, long philtrum and short neck. Rare unusual associated findings included microdontia, teeth spacing, delayed eruption, prominent angulation of the lumbar‐sacral junction and atrial septal defect. Mutational analysis revealed 10 different homozygous CHST3 (NM_004273.5) variants including 7 missense, two frameshift and one nonsense variant. Of them, the c.384_391dup (p.Pro131Argfs*88) was recurrent in two families. Eight of these variants were not described before. Our study presents the largest series of patients with CHST3‐related skeletal dysplasia from the same ethnic group. Furthermore, it reinforces that lethal cardiac involvement is a critical clinical finding of the disorder. Therefore, we believe that our study expands the phenotypic and mutational spectrum, and also highlights the importance of performing echocardiography in patients harboring CHST3 variants.
ABSTRACT
Most reported mutations in the FGFR3 gene are dominant activating mutations that cause a variety of short‐limbed bone dysplasias including achondroplasia and syndromic craniosynostosis. We ...report the phenotype and underlying molecular abnormality in two brothers, born to first cousin parents. The clinical picture is characterized by tall stature and severe skeletal abnormalities leading to inability to walk, with camptodactyly, arachnodactyly, and scoliosis. Whole exome sequencing revealed a homozygous novel missense mutation in the FGFR3 gene in exon 12 (NM_000142.4:c.1637C>A: p.(Thr546Lys)). The variant is found in the kinase domain of the protein and is predicted to be pathogenic. It is located near a known hotspot for hypochondroplasia. This is the first report of a homozygous loss‐of‐function mutation in FGFR3 in human that results in a skeletal overgrowth syndrome.
Summary
This study describes the clinical, radiological, and molecular data of four new patients with osteoporosis-pseudoglioma syndrome and assesses their response to bisphosphonate therapy.
...Introduction
Osteoporosis-pseudoglioma syndrome (OPPG) is a very rare disorder characterized mainly by severe juvenile osteoporosis and congenital blindness. OPPG is caused by biallelic mutations in the gene encoding low-density lipoprotein receptor-related protein 5 (
LRP5
).
Methods
We present the clinical, radiological, and molecular findings of four new patients with OPPG from Egypt. We also assessed patients’ response to oral and intravenous bisphosphonate therapy.
Results
All patients had reduced bone mineral density (BMD) with variable number of fractures per year, in addition to bone abnormalities and the characteristic eye phenotype associated with OPPG. Mutation analyses of
LRP5
gene revealed three different homozygous variants including two novel ones, c.7delG (p.A3Qfs*80) and c.3280G > A (p.E1094K). The c.3280G > A (p.E1094K) was recurrent in two unrelated patients who shared a unique haplotype suggesting a possible founder effect. The use of bisphosphonate therapy was beneficial; however, intravenous bisphosphonate administration led to a more favorable response.
Conclusion
Our study described the phenotypic and genetic features of four patients with OPPG and identified two new
LRP5
variants, thus expanding the mutational spectrum of OPPG. In addition, our study reinforces the efficiency of using intravenous bisphosphonates in the management of patients with OPPG.
Orofaciodigital syndrome (OFD) is a genetically heterogeneous ciliopathy characterized by anomalies of the oral cavity, face, and digits. We describe individuals with OFD from three unrelated ...families having bi-allelic loss-of-function variants in SCNM1 as the cause of their condition. SCNM1 encodes a protein recently shown to be a component of the human minor spliceosome. However, so far the effect of loss of SCNM1 function on human cells had not been assessed. Using a comparative transcriptome analysis between fibroblasts derived from an OFD-affected individual harboring SCNM1 mutations and control fibroblasts, we identified a set of genes with defective minor intron (U12) processing in the fibroblasts of the affected subject. These results were reproduced in SCNM1 knockout hTERT RPE-1 (RPE-1) cells engineered by CRISPR-Cas9-mediated editing and in SCNM1 siRNA-treated RPE-1 cultures. Notably, expression of TMEM107 and FAM92A encoding primary cilia and basal body proteins, respectively, and that of DERL2, ZC3H8, and C17orf75, were severely reduced in SCNM1-deficient cells. Primary fibroblasts containing SCNM1 mutations, as well as SCNM1 knockout and SCNM1 knockdown RPE-1 cells, were also found with abnormally elongated cilia. Conversely, cilia length and expression of SCNM1-regulated genes were restored in SCNM1-deficient fibroblasts following reintroduction of SCNM1 via retroviral delivery. Additionally, functional analysis in SCNM1-retrotransduced fibroblasts showed that SCNM1 is a positive mediator of Hedgehog (Hh) signaling. Our findings demonstrate that defective U12 intron splicing can lead to a typical ciliopathy such as OFD and reveal that primary cilia length and Hh signaling are regulated by the minor spliceosome through SCNM1 activity.
This work uncovers bi-allelic loss-of-function mutations in SCNM1 as a cause of orofaciodigital syndrome. Absence of SCNM1 impairs the minor intron splicing process leading to changes in the expression of genes, some of which are directly related to primary cilia. As a result, cilia length and hedgehog signaling are altered.
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