Genetic diseases of the Kennedy pathways for membrane synthesis

The two branches of the Kennedy pathways (CDP-choline and CDP-ethanolamine) are the predominant pathways responsible for the synthesis of the most abundant phospholipids, phosphatidylcholine and phosphatidylethanolamine, respectively, in mammalian membranes. Recently, hereditary diseases associated with single gene mutations in the Kennedy pathways have been identified. Interestingly, genetic diseases within the same pathway vary greatly, ranging from muscular dystrophy to spastic paraplegia to a childhood blinding disorder to bone deformations. Indeed, different point mutations in the same gene (PCYT1; CCTα) result in at least three distinct diseases. In this review, we will summarize and review the genetic diseases associated with mutations in genes of the Kennedy pathway for phospholipid synthesis. These single-gene disorders provide insight, indeed direct genotype-phenotype relationships, into the biological functions of specific enzymes of the Kennedy pathway. We discuss potential mechanisms of how mutations within the same pathway can cause disparate disease.

Spondylo-epiphyseal dysplasia in two sibs due to a homozygous splicing variant in COL2A1

Type 2 collagenopathies encompass a large group of chondrodysplasias ranging from the perinatally lethal achondrogenesis type 2 and hypochondrogenesis at the severe end of the spectrum to early-onset osteoarthritis with normal stature at the milder end of the spectrum. With the exception of a few reported cases, these dysplasias are predominantly caused by heterozygous variants in the COL2A1 gene and hence show an autosomal dominant inheritance pattern. Here we report on two siblings, originating from a consanguineous family, who presented with disproportionate short stature, ocular abnormalities, cleft palate and hearing impairment. The radiographic study showed signs of a spondyloepiphyseal dysplasia, compatible with a type 2 collagen disorder. Indeed, both siblings were homozygous for a c.3111+2T > Cp.(Glu1033Lysfs*5) splice site variant in the COL2A1 gene. cDNA analysis performed on skin fibroblasts from the affected sibs revealed the co-occurrence of the wild-type transcript and an aberrant splice product, the latter believed to be degraded by nonsense-mediated mRNA decay. The parents who were heterozygous for this variant were phenotypically normal. This paper confirms that type 2 collagenopathies can show an autosomal recessive inheritance.

Novel progressive acrodysostosis-like skeletal dysplasia, cerebellar atrophy, and ichthyosis

Acrodysostosis refers to a rare heterogeneous group of bone dysplasias that share skeletal features, hormone resistance, and intellectual disability. Two genes have been associated with acrodysostosis with or without hormone resistance (PRKAR1A and PDE4D). Severe intellectual disability has been reported with acrodysostosis but brain malformations and ichthyosis have not been reported in these syndromes. Here we describe a female patient with acrodysostosis, intellectual disability, cerebellar hypoplasia, and lamellar ichthyosis. The patient has an evolving distinctive facial phenotype and childhood onset ataxia. X-rays showed generalized osteopenia, shortening of middle and distal phalanges, and abnormal distal epiphysis of the ulna and radius. Brain magnetic resonance imaging showed cerebellar atrophy without other brainstem abnormalities. Genetic workup included nondiagnostic chromosomal microarray and skeletal dysplasia molecular panels. These clinical findings are different from any recognized form of acrodysostosis syndrome. Whole exome sequencing did not identify rare or predicted pathogenic variants in genes associated with known acrodysostosis, lamellar ichthyosis, and other overlapping disorders. A broader search for rare alleles absent in healthy population databases and controls identified two heterozygous truncating alleles in FBNL7 and PPM1M genes, and one missense allele in the NPEPPS gene. Identification of additional patients is required to delineate the mechanism of this unique disorder.

Microcephalic osteodysplastic primordial dwarfism type II and pachygyria: Morphometric analysis in a 2-year-old girl

Microcephalic osteodysplastic primordial dwarfism (MOPD) type II is a rare disorder characterized by skeletal dysplasia, severe proportionate short stature, insulin resistance and cerebrovascular abnormalities including cerebral aneurysms and moyamoya disease. MOPD type II is caused by mutations in the pericentrin (PCNT) gene, which encodes a protein involved in centrosomes function. We report a 2 year old girl affected by MOPD type II caused by two compound heterozygous loss-of-function variants in PCNT gene, of which one is a novel variant (c.5304delT; p.Gly1769AlafsTer34). The patient presented atypical brain magnetic resonance imaging (MRI) findings consistent with pachygyria. This was confirmed by morphometric analysis of cortical thickness (CT) and gyrification index by comparing MRI data of the patient with a group of eight age-matched healthy controls. The statistical analysis revealed a significant and diffuse increase of CT with an anterior-predominant pattern and diffuse reduced gyrification (p < .05). These findings provide new evidences to the emergent concept that malformations of cortical development are complex disorders and that new genetic findings contribute to the fading of classification borders.

A new case of Greenberg dysplasia and literature review suggest that Greenberg dysplasia, dappled diaphyseal dysplasia, and Astley-Kendall dysplasia are allelic disorders

BACKGROUND

Greenberg dysplasia is a rare, autosomal recessive, prenatal lethal bone dysplasia caused by biallelic pathogenic variants in the lamin B receptor (LBR) gene. Pathogenic variants in LBR are also associated with Pelger-Huët anomaly, an autosomal dominant benign abnormality of the nuclear shape and chromatin organization of blood granulocytes, and Pelger-Huët anomaly with variable skeletal anomalies, a mild, regressing to moderate-severe autosomal recessive condition. Conditions with abnormal sterol metabolism and different genetic basis have clinical and radiographic features similar to Greenberg dysplasia, for example X-linked dominant chondrodysplasia punctata, Conradi-Hünermann type, and CHILD syndrome, and other conditions with unknown genetic etiology display very similar features, for example, dappled diaphyseal dysplasia and Astley-Kendall dysplasia.

METHODS

We present a fetus with typical clinical and radiographic features of Greenberg dysplasia, and review the literature.

RESULTS

Genetic testing confirmed the diagnosis Greenberg dysplasia: homozygosity for a pathogenic variant in LBR.

CONCLUSION

Comparing the clinical and radiographic phenotypes of Greenberg dysplasia, dappled diaphyseal dysplasia, and Astley-Kendall dysplasia, we suggest that these are allelic disorders.

The Connective Tissue Disorder Associated with Recessive Variants in the SLC39A13 Zinc Transporter Gene (Spondylo-Dysplastic Ehlers-Danlos Syndrome Type 3): Insights from Four Novel Patients and Follow-Up on Two Original Cases

Recessive loss-of-function variants in SLC39A13, a putative zinc transporter gene, were first associated with a connective tissue disorder that is now called “Ehlers–Danlos syndrome, spondylodysplastic form type 3” (SCD-EDS, OMIM 612350) in 2008. Nine individuals have been described. We describe here four additional affected individuals from three consanguineous families and the follow up of two of the original cases. In our series, cardinal findings included thin and finely wrinkled skin of the hands and feet, characteristic facial features with downslanting palpebral fissures, mild hypertelorism, prominent eyes with a paucity of periorbital fat, blueish sclerae, microdontia, or oligodontia, and—in contrast to most types of Ehlers–Danlos syndrome—significant short stature of childhood onset. Mild radiographic changes were observed, among which platyspondyly is a useful diagnostic feature. Two of our patients developed severe keratoconus, and two suffered from cerebrovascular accidents in their twenties, suggesting that there may be a vascular component to this condition. All patients tested had a significantly reduced ratio of the two collagen-derived crosslink derivates, pyridinoline-to-deoxypyridinoline, in urine, suggesting that this simple test is diagnostically useful. Additionally, analysis of the facial features of affected individuals by DeepGestalt technology confirmed their specificity and may be sufficient to suggest the diagnosis directly. Given that the clinical presentation in childhood consists mainly of short stature and characteristic facial features, the differential diagnosis is not necessarily that of a connective tissue disorder and therefore, we propose that SLC39A13 is included in gene panels designed to address dysmorphism and short stature. This approach may result in more efficient diagnosis.

Characterisation of ACP5 missense mutations encoding tartrate-resistant acid phosphatase associated with spondyloenchondrodysplasia

Biallelic mutations in ACP5, encoding tartrate-resistant acid phosphatase (TRACP), have recently been identified to cause the inherited immuno-osseous disorder, spondyloenchondrodysplasia (SPENCD). This study was undertaken to characterize the eight reported missense mutations in ACP5 associated with SPENCD on TRACP expression. ACP5 mutant genes were synthesized, transfected into human embryonic kidney (HEK-293) cells and stably expressing cell lines were established. TRACP expression was assessed by cytochemical and immuno-cytochemical staining with a panel of monoclonal antibodies. Analysis of wild (WT) type and eight mutant stable cell lines indicated that all mutants lacked stainable enzyme activity. All ACP5 mutant constructs were translated into intact proteins by HEK-293 cells. The mutant TRACP proteins displayed variable immune reactivity patterns, and all drastically reduced enzymatic activity, revealing that there is no gross inhibition of TRACP biosynthesis by the mutations. But they likely interfere with folding thereby impairing enzyme function. TRACP exists as two isoforms. TRACP 5a is a less active monomeric enzyme (35kD), with the intact loop peptide and TRACP 5b is proteolytically cleaved highly active enzyme encompassing two subunits (23 kD and 16 kD) held together by disulfide bonds. None of the mutant proteins were proteolytically processed into isoform 5b intracellularly, and only three mutants were secreted in significant amounts into the culture medium as intact isoform 5a-like proteins. Analysis of antibody reactivity patterns revealed that T89I and M264K mutant proteins retained some native conformation, whereas all others were in “denatured” or “unfolded” forms. Western blot analysis with intracellular and secreted TRACP proteins also revealed similar observations indicating that mutant T89I is amply secreted as inactive protein. All mutant proteins were attacked by Endo-H sensitive glycans and none could be activated by proteolytic cleavage in vitro. In conclusion, determining the structure-function relationship of the SPENCD mutations in TRACP will expand our understanding of basic mechanisms underlying immune responsiveness and its involvement in dysregulated bone metabolism.

Transcriptome analysis of MAPK signaling pathway and associated genes to angiogenesis in chicken erythrocytes on response to thiram-induced tibial lesions

This study was planned to investigate TD (Tibial dyschondroplasia) on the potential MAPK signaling pathway and angiogenesis related genes. Forty-eight broilers were allotted into control (C) and treatment (T) groups of 2, 6 and 15 days as C1, C2, C3, T1, T2 and T3. The histopathology results revealed that tibiotarsus bone of chickens had more lesions on day 6 (T2 group). The chondrocytes were disordered, and the size, shape and proliferation were affected. Transcriptome results revealed that differentially expressed genes (DEGs) identified were 63, 1026, 623, 130, 141 and 146 in C1 (2 days control vs 6 days control); C2 (2 days control vs 15 days control); C3 (6 days control vs 15 days control); T1 (2 days treatment vs 6 days treatment); T2 (2 days treatment vs 15 days treatment) and T3 (6 days treatment vs 15 days treatment) groups respectively. Whereas, 10 angiogenesis related-genes RHOC, MEIS2, BAIAP2, TGFBI, KLF2, CYR61, PTPN11, PLXNC1, HSPH1 and NRP2 were downregulated on day 6 in the treatment group. The pathway which was found enriched in the control and treatment groups was MAPK signaling pathway. Therefore selected 10 MAPK signaling pathway-related genes RAC2, MAP3K1, PRKCB, FLNB, IL1R1, PTPN7, RPS6KA, MAP3K6, GNA12 and HSPA8 which were found significantly downregulated in the treatment group on day 6. It is concluded that angiogenesis and MAPK signaling pathway related genes has an essential role in TD, as those top screened genes found downregulated in the thiram fed chickens when TD observed severed on day 6.

XBP1 signalling is essential for alleviating mutant protein aggregation in ER-stress related skeletal disease

The unfolded protein response (UPR) is a conserved cellular response to the accumulation of proteinaceous material in endoplasmic reticulum (ER), active both in health and disease to alleviate cellular stress and improve protein folding. Multiple epiphyseal dysplasia (EDM5) is a genetic skeletal condition and a classic example of an intracellular protein aggregation disease, whereby mutant matrilin-3 forms large insoluble aggregates in the ER lumen, resulting in a specific 'disease signature' of increased expression of chaperones and foldases, and alternative splicing of the UPR effector XBP1. Matrilin-3 is expressed exclusively by chondrocytes thereby making EDM5 a perfect model system to study the role of protein aggregation in disease. In order to dissect the role of XBP1 signalling in aggregation-related conditions we crossed a p.V194D Matn3 knock-in mouse model of EDM5 with a mouse line carrying a cartilage specific deletion of XBP1 and analysed the resulting phenotype. Interestingly, the growth of mice carrying the Matn3 p.V194D mutation compounded with the cartilage specific deletion of XBP1 was severely retarded. Further phenotyping revealed increased intracellular retention of amyloid-like aggregates of mutant matrilin-3 coupled with dramatically decreased cell proliferation and increased apoptosis, suggesting a role of XBP1 signalling in protein accumulation and/or degradation. Transcriptomic analysis of chondrocytes extracted from wild type, EDM5, Xbp1-null and compound mutant lines revealed that the alternative splicing of Xbp1 is crucial in modulating levels of protein aggregation. Moreover, through detailed transcriptomic comparison with a model of metaphyseal chondrodysplasia type Schmid (MCDS), an UPR-related skeletal condition in which XBP1 was removed without overt consequences, we show for the first time that the differentiation-state of cells within the cartilage growth plate influences the UPR resulting from retention of a misfolded mutant protein and postulate that modulation of XBP1 signalling pathway presents a therapeutic target for aggregation related conditions in cells undergoing proliferation.

Five-year follow-up outcomes of comprehensive rehabilitation in Korean siblings with cerebral, ocular, dental, auricular, skeletal anomalies (CODAS) syndrome: A case report

RATIONALE

Cerebral, ocular, dental, auricular, skeletal anomalies (CODAS) syndrome is a very rare multisystem disorder, which shows malformations of the central nervous system, ears, eyes, teeth, and skeleton that was first reported in 1991. Only a few cases that sporadically occurred have been reported worldwide. The research investigating the pathogenesis and patterns of CODAS inheritance is still ongoing. There is no satisfactory treatment for this rare genetic disease yet. Due to the lack of curative medical treatment, rehabilitation could play a major role in treatment for genetic disease.

PATIENT CONCERNS

To our best knowledge, the 2 children described in this study are the only CODAS syndromes siblings reported in the world so far. These Korean siblings show highly distinctive features consisting of developmental delay, cataracts, vulnerability to tooth decay, epiphyseal dysplasia, and anomalous ears.

DIAGNOSES

CODAS syndrome.

INTERVENTIONS

Comprehensive long-term rehabilitation treatment during 5 years.

OUTCOMES

We report on the progress of the comprehensive long-term rehabilitation treatment at 5-year follow-up. Their fine motor and language skills development improved similarly to that of same-aged children. We observed the positive effect of rehabilitation on the quality of life.

LESSONS

The therapy of genetic disorders is challenging for pediatric neurologists and pediatric physiatrists. We suggest that rehabilitation is the best treatment currently available for this genetic disease that yields satisfactory therapeutic effect.

Bi-allelic CSF1R Mutations Cause Skeletal Dysplasia of Dysosteosclerosis-Pyle Disease Spectrum and Degenerative Encephalopathy with Brain Malformation

Colony stimulating factor 1 receptor (CSF1R) plays key roles in regulating development and function of the monocyte/macrophage lineage, including microglia and osteoclasts. Mono-allelic mutations of CSF1R are known to cause hereditary diffuse leukoencephalopathy with spheroids (HDLS), an adult-onset progressive neurodegenerative disorder. Here, we report seven affected individuals from three unrelated families who had bi-allelic CSF1R mutations. In addition to early-onset HDLS-like neurological disorders, they had brain malformations and skeletal dysplasia compatible to dysosteosclerosis (DOS) or Pyle disease. We identified five CSF1R mutations that were homozygous or compound heterozygous in these affected individuals. Two of them were deep intronic mutations resulting in abnormal inclusion of intron sequences in the mRNA. Compared with Csf1r-null mice, the skeletal and neural phenotypes of the affected individuals appeared milder and variable, suggesting that at least one of the mutations in each affected individual is hypomorphic. Our results characterized a unique human skeletal phenotype caused by CSF1R deficiency and implied that bi-allelic CSF1R mutations cause a spectrum of neurological and skeletal disorders, probably depending on the residual CSF1R function.

Bi-allelic Variants in TONSL Cause SPONASTRIME Dysplasia and a Spectrum of Skeletal Dysplasia Phenotypes

SPONASTRIME dysplasia is an autosomal-recessive spondyloepimetaphyseal dysplasia characterized by spine (spondylar) abnormalities, midface hypoplasia with a depressed nasal bridge, metaphyseal striations, and disproportionate short stature. Scoliosis, coxa vara, childhood cataracts, short dental roots, and hypogammaglobulinemia have also been reported in this disorder. Although an autosomal-recessive inheritance pattern has been hypothesized, pathogenic variants in a specific gene have not been discovered in individuals with SPONASTRIME dysplasia. Here, we identified bi-allelic variants in TONSL, which encodes the Tonsoku-like DNA repair protein, in nine subjects (from eight families) with SPONASTRIME dysplasia, and four subjects (from three families) with short stature of varied severity and spondylometaphyseal dysplasia with or without immunologic and hematologic abnormalities, but no definitive metaphyseal striations at diagnosis. The finding of early embryonic lethality in a Tonsl-/- murine model and the discovery of reduced length, spinal abnormalities, reduced numbers of neutrophils, and early lethality in a tonsl-/- zebrafish model both support the hypomorphic nature of the identified TONSL variants. Moreover, functional studies revealed increased amounts of spontaneous replication fork stalling and chromosomal aberrations, as well as fewer camptothecin (CPT)-induced RAD51 foci in subject-derived cell lines. Importantly, these cellular defects were rescued upon re-expression of wild-type (WT) TONSL; this rescue is consistent with the hypothesis that hypomorphic TONSL variants are pathogenic. Overall, our studies in humans, mice, zebrafish, and subject-derived cell lines confirm that pathogenic variants in TONSL impair DNA replication and homologous recombination-dependent repair processes, and they lead to a spectrum of skeletal dysplasia phenotypes with numerous extra-skeletal manifestations.

Phenotyping and genotyping of skeletal dysplasias: Evolution of a center and a decade of experience in India

Genetic heterogeneity, high burden and the paucity of genetic testing for rare diseases challenge genomic healthcare for these disorders in India. Here we report our experience over the past decade, of establishing the genomic evaluation of skeletal dysplasia at a tertiary university hospital in India. Research or clinical genomic testing was carried out by Sanger sequencing and next-generation sequencing. Close national and international collaborations aided phenotyping and genotyping. We report 508 families (557 affected individuals) with the definitive molecular diagnosis of skeletal dysplasia. Dysostoses multiplex (n = 196), genetic inflammatory/rheumatoid-like osteoarthropathies (n = 114) and osteogenesis imperfecta and decreased bone density (n = 58) were the most common diagnoses. We enumerate the processes, clinical diagnoses and causal variants in the cohort with 48 novel variants in 21 genes. We summarize scientific contributions of the center to the description of clinical and mutation profiles and discovery of new phenotypes and genetic etiology. Our study illustrates the establishment and application of genomic testing tools for genetic disorders of skeleton in a large cohort. We believe this could be a model to emulate for other developing genetic centers.

Lamin B receptor-related disorder is associated with a spectrum of skeletal dysplasia phenotypes

LBR (Lamin B Receptor) encodes a bifunctional protein important for cholesterol biosynthesis and heterochromatin organization on the inner nuclear membrane. Pathogenic variants in LBR are associated with marked phenotypic variability, ranging from the benign Pelger-Huët anomaly to lethal Greenberg Dysplasia. We performed trio exome sequencing (ES) on two patients with atypical variants of skeletal dysplasia and their unaffected parents. Patient 1 exhibited frontal bossing, mid-face hypoplasia, short stature with rhizomelic limb shortening, and relative macrocephaly at birth. Although remained short, Patient 1 later showed spontaneous improvement in her skeletal findings. Exome sequencing revealed two novel variants in LBR, c.1504C > G (p.Arg502Gly) in exon 12 and c.1748G > T (p.Arg583Leu) in exon 14, which were inherited from her unaffected father and mother, respectively. Sterol analysis revealed an increased level of cholesta‑8,14‑dien‑3β‑ol to 2.9% of total sterols, consistent with a functional deficiency of 3β‑hydroxysterol Δ14‑reductase. Patient 2 presented at birth with short stature and marked rhizomelic limb shortening but later exhibited decreasing severity of shortening of the long bones and improvement in the radiographic skeletal abnormalities although he continued to be significantly short at age 10 years. Exome sequencing revealed that Patient 2 is homozygous for a pathogenic variant c.1534C > T (p.Arg512Trp) in exon 12 of LBR, which was inherited from his unaffected consanguineous parents. This report provides further evidence for a phenotypic spectrum of LBR-associated disorders and expands the genotypic spectrum by describing 3 novel disease-causing variants that have not been previously associated with a disease. Moreover, our data on Patient 1 demonstrate that variants throughout the gene appear to influence both the sterol reductase and nuclear functions of LBR.

Morphometric analysis of thoracic aorta in Slc39a13/Zip13-KO mice

Ehlers-Danlos syndrome (EDS) is a collection of inheritable diseases involving the musculoskeletal, integumentary and visual systems. Spondylodysplastic EDS-ZIP13 (spEDS-ZIP13: OMIM 612350) was recently defined as a new form of EDS. Although vasculitis has been found in many spEDS-ZIP13 patients, vascular pathology has not been included as a pathognomonic lesion of this type of EDS. We investigate the morphometry of the thoracic aorta in wild-type and Zip13-knockout (Zip13-KO) mice. Our assessment found abnormalities in the number and morphology of elastic and cellular components in the aortic wall, especially the tunica media, of Zip13-KO mice, indicating aortic fragility. Accordingly, our major findings (vascular smooth muscle cells with small nuclei, small percentage of elastic membrane area per tunica media, many large elastic flaps) should be considered vulnerable characteristics indicating fragility of the aorta in patients with spEDS-ZIP13.

Mesencephalic astrocyte-derived neurotropic factor is an important factor in chondrocyte ER homeostasis

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum (ER) resident protein that can be secreted due to an imperfect KDEL motif. MANF plays a cytoprotective role in several soft tissues and is upregulated in conditions resulting from intracellular retention of mutant protein, including two skeletal diseases, metaphyseal chondrodysplasia, Schmid type (MCDS) and multiple epiphyseal dysplasia (MED). The role of MANF in skeletal tissue homeostasis is currently unknown. Interestingly, cartilage-specific deletion of Manf in a mouse model of MED resulted in increased disease severity, suggesting its upregulation may be chondroprotective. Treatment of MED chondrocytes with exogenous MANF led to a decrease in the cellular levels of BiP (GRP78), confirming MANF's potential to modulate ER stress responses. However, it did not alleviate the intracellular retention of mutant matrilin-3, suggesting that it is the intracellular MANF that is of importance in the pathobiology of skeletal dysplasias. The Col2Cre-driven deletion of Manf from mouse cartilage resulted in a chondrodysplasia-like phenotype. Interestingly, ablation of MANF in cartilage did not have extracellular consequences but led to an upregulation of several ER-resident chaperones including BiP. This apparent induction of ER stress in turn led to dysregulated chondrocyte apoptosis and decreased proliferation, resulting in reduced long bone growth. We have previously shown that ER stress is an underlying disease mechanism for several skeletal dysplasias. The cartilage-specific deletion of Manf described in this study phenocopies our previously published chondrodysplasia models, further confirming that ER stress itself is sufficient to disrupt skeletal growth and thus represents a potential therapeutic target.

Early-onset dementia, leukoencephalopathy and brain calcifications: a clinical, imaging and pathological comparison of ALSP and PLOSL/Nasu Hakola disease

Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia, and Nasu Hakola disease or polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy are both underrecognized progressive degenerative white matter diseases that can present with young dementia, leukoencephalopathy and brain calcifications. We report and compare three cases in terms of clinical phenotype, imaging and neuropathological findings. Both cases have led to the identification of two novel causal mutations.

Tauopathy-associated PERK alleles are functional hypomorphs that increase neuronal vulnerability to ER stress

Tauopathies are neurodegenerative diseases characterized by tau protein pathology in the nervous system. EIF2AK3 (eukaryotic translation initiation factor 2 alpha kinase 3), also known as PERK (protein kinase R-like endoplasmic reticulum kinase), was identified by genome-wide association study as a genetic risk factor in several tauopathies. PERK is a key regulator of the Unfolded Protein Response (UPR), an intracellular signal transduction mechanism that protects cells from endoplasmic reticulum (ER) stress. PERK variants had previously been identified in Wolcott-Rallison Syndrome, a rare autosomal recessive metabolic disorder, and these variants completely abrogated the function of PERK's kinase domain or prevented PERK expression. In contrast, the PERK tauopathy risk variants were distinct from the Wolcott-Rallison variants and introduced missense alterations throughout the PERK protein. The function of PERK tauopathy variants and their effects on neurodegeneration are unknown. Here, we discovered that tauopathy-associated PERK alleles showed reduced signaling activity and increased PERK protein turnover compared to protective PERK alleles. We found that iPSC-derived neurons carrying PERK risk alleles were highly vulnerable to ER stress-induced injury with increased tau pathology. We found that chemical inhibition of PERK in human iPSC-derived neurons also increased neuronal cell death in response to ER stress. Our results indicate that tauopathy-associated PERK alleles are functional hypomorphs during the UPR. We propose that reduced PERK function leads to neurodegeneration by increasing neuronal vulnerability to ER stress-associated damage. In this view, therapies to enhance PERK signaling would benefit at-risk carriers of hypomorphic alleles.

Recessive multiple epiphyseal dysplasia - Clinical characteristics caused by rare compound heterozygous SLC26A2 genotypes

Pathogenic sequence variants in the solute carrier family 26 member 2 (SLC26A2) gene result in lethal (achondrogenesis Ib and atelosteogenesis II) and non-lethal (diastrophic dysplasia and recessive multiple epiphyseal dysplasia, rMED) chondrodysplasias. We report on two new patients with rMED and very rare compound heterozygous mutation combinations in non-consanguineous families. Patient I presented in childhood with waddling gait and joint stiffness. Radiographs showed epiphyseal changes, bilateral coxa plana-deformity and knee valgus deformity, for which he underwent surgeries. At present 33 years his height is 165 cm. Patient II presented with cleft palate, small jaw, short limbs, underdeveloped thumbs and on radiographs, cervical kyphosis with an underdeveloped C4. He also developed severe scoliosis but has grown at -2.9 SD curve. Molecular analysis revealed that patient I is heterozygous for two known pathogenic variants in SLC26A2, a splice site variant c.-26+2T > C and a missense variant c.1957T > A (p.Cys653Ser), while patient II is compound heterozygous for missense variants c.835C > T (p.Arg279Trp) and c.1535C > A (p.Thr512Lys). These patients further elucidate the variability of the phenotypic and genetic presentations of rMED.

Proposal of patient-specific growth plate cartilage xenograft model for FGFR3 chondrodysplasia

OBJECTIVE

FGFR3 chondrodysplasia is caused by a gain-of-function mutation of the FGFR3 gene. The disease causes abnormal growth plate cartilage and lacks effective drug treatment. We sought to establish an in vivo model for the study of FGFR3 chondrodysplasia pathology and drug testing.

DESIGN

We created cartilage from human induced pluripotent stem cells (hiPSCs) and transplanted the cartilage into the subcutaneous spaces of immunodeficient mice. We then created cartilage from the hiPSCs of patients with FGFR3 chondrodysplasia and transplanted them into immunodeficient mice. We treated some mice with a FGFR inhibitor after the transplantation.

RESULTS

Xenografting the hiPSC-derived cartilage reproduced human growth plate cartilage consisting of zones of resting, proliferating, prehypertrophic and hypertrophic chondrocytes and bone in immunodeficient mice. Immunohistochemistry of xenografts using anti-human nuclear antigen antibody indicated that all chondrocytes in growth plate cartilage were human, whereas bone was composed of human and mouse cells. The pathology of small hypertrophic chondrocytes due to up-regulated FGFR3 signaling in FGFR3 skeletal dysplasia was recapitulated in growth plate cartilage formed in the xenografts of patient-specific hiPSC-derived cartilage. The mean diameters of hypertrophic chondrocytes between wild type and thanatophoric dysplasia were significantly different (95% CI: 13.2-26.9; n = 4 mice, one-way analysis of variance (ANOVA)). The pathology was corrected by systemic administration of a FGFR inhibitor to the mice.

CONCLUSION

The patient-specific growth plate cartilage xenograft model for FGFR3 skeletal dysplasia indicated recapitulation of pathology and effectiveness of a FGFR inhibitor for treatment and warrants more study for its usefulness to study disease pathology and drug testing.

Does Adenovirus and Coxsackie B Virus Infection Play a Role in Tracheobronchopathia Osteochondroplastica (TO)

<i>Background:</i> Tracheobronchopathia osteochondroplastica (TO) is a rare benign disease. We report a case of TO. <i>Methods:</i> Chest CT scan and bronchoscope with biopsy was performed for diagnosis and blood tests explored for the latent etiology. <i>Results:</i> Chest CT scan and bronchoscopic images showed multiple nodular protrusions in the trachea and main bronchi. Histopathology demonstrated sub-mucosal ossification and inflammatory cell infiltration. Laboratory inspection showed adenovirus and coxsackie B virus IgM antibodies were positive. <i>Conclusions:</i> The patient recently had a virus infection and inflammation was observed in histopathology, which indicated adenovirus and coxsackie B virus may play a role in the occurrence or exacerbation of TO.

Effect of tetramethyl thiuram disulfide (thiram) in relation to tibial dyschondroplasia in chickens

Tetramethyl thiuram disulfide (thiram) is one of the important pesticides, which is extensively used in agriculture, but if it is combined with the cell membrane, then it causes membrane damage, bone morphogenic inactivation, and inhibited angiogenesis. Thiram has been considered a common cause of tibial dyschondrolplasia (TD) in various avian species, because it becomes the part of feed due to environmental contamination and its overuse in agriculture as pesticides or fungicide. However, there is no systematic study on the changes of the correlation indexes with toxic effect of the thiram in chickens. Therefore, we evaluated the toxic effects of thiram on growth performance of chickens, viscera organ index, pathological changes in tissue, and gene expression associated with osteoblast differentiation, vascularization, and tibial bone development. For this study, 1-day chickens (n = 300) were randomly distributed into two equal groups, control group (normal basal diet) and thiram group (adding thiram 40 mg/kg in basal diet). The result presented that thiram group chickens were looking unhealthy, lazy, and showing clinical symptoms like lameness. Thiram treatment significantly reduced the performance of chickens, liver index, and tibial length compared with control group. The toxic effect of thiram increased the visceral organ index (spleen and cardiac), tibia index, and TD severity considerably. It also increased serum Ca²⁺ and P³⁺ concentration and decreased tibial density compared to control chickens but the difference was not significant. Histopathology of tibia and liver showed that there were severe lesions due to toxic effect of thiram. Furthermore, HIF-1α and VEGF antibody localizations were increased and WNT4 localization was reduced significantly in immunohistochemical analysis. This systemic study of toxic effects of thiram in chicken concluded that thiram reduced the growth performance of chickens through decreasing liver index, whereas increasing kidney, cardiac, and spleen index, and induced TD by changing the expressions of VEGF, HIF-1α, and WNT4.

Paradoxical roles of ATF6α and ATF6β in modulating disease severity caused by mutations in collagen X

Whilst the role of ATF6α in modulating the unfolded protein response (UPR) has been well documented, the function of its paralogue ATF6β is less well understood. Using knockdown in cell culture and gene ablation in mice we have directly compared the roles of ATF6α & β in responding to the increased ER stress induced by mutant forms of type X collagen that cause the ER stress-associated metaphyseal chondrodysplasia type Schmid (MCDS). ATF6α more efficiently deals with the disease-associated ER stress in the absence of ATF6β and conversely, ATF6β is less effective in the absence of ATF6α. Furthermore, disease severity in vivo is increased by ATF6α ablation and decreased by ATF6β ablation. In addition, novel functions for each paralogue are described including an ATF6β-specific role in controlling growth plate chondrocyte proliferation. The clear demonstration of the intimate relationship of the two ATF6 isoforms and how ATF6β can moderate the activity of ATF6α and vice versa is of great significance for understanding the UPR mechanism. The activities of both ATF6 isoforms and their separate roles need consideration when deciding how to target increased ER stress as a means of treating MCDS and other ER stress-associated diseases.

Hypoparathyroidism in children: a study of eight cases

BACKGROUND

Hypoparathyroidism is a rare pediatric endocrine disease, which is caused by low circulating levels of PTH or insensitivity to its action in the target tissues.

AIM

To report the clinical and biochemical characteristics and theoutcome of 8 patients with hypoparathyroidism.

METHODS

We analyzed retrospectively the results of clinical, biochemical, radiological findings of patients with hypoparathyroidism diagnosed in pediatric department of Hedi Chaker Hospital during the period 1994-2013.

RESULTS

Eight patients (5 females and 3 males) were diagnosed with hypoparathyroidism during 20 years's period. The median age at the onset of first symptoms was 17,5 months (15 days- 5 years and 10 months). Seizures were the most commonly presenting symptom and were seen in seven cases. Eight patients were diagnosed with hypoparathyroidism (Di-Georges syndrome: one case, Sanjad Sakati syndrome: 3 case, kearns sayre syndrome: 1 case, autoimmune polyendocrinopathy candidiasis- ectodermal dystrophy: one case, idiopathic hypoparathyroidism: two cases. Conventional treatment was based on calcium and vitamin D analogs. The average of follow up was 5 years. Nephrocalcinosis was noted in two patients. The death occurred in five patients; it was related to hypocalcaemia in one patient.

CONCLUSION

The diagnosis of hyperparathyroidism is easy; it's established on the association of hypocalcaemia and hyperphosphatemia. Etiologic approach is based on molecular findings. Vitamin D analog treatment of hypoparathyroidism in children involves the challenge, of adjusting treatment dosage to minimize both symptomatic hypocalcemia and asymptomatic, but potentially kidney-damaging, hypercalciuria causing nephrocalcinosis and renal insufficiency.