Autosomal Recessive Form Research Articles

Genetic Analysis of Heterotaxy in a Consanguineous Cohort.

Heterotaxy (HTX) is a group of clinical conditions with a shared pathology of dislocation of one or more organs along the left-right axis. The etiology of HTX is tremendously heterogeneous spanning environmental factors, chromosomal aberrations, mono/oligogenic variants, and complex inheritance. However, in the vast majority of cases, the etiology of HTX remains elusive. Here, we sought to describe the yield of genetic analysis and spectrum of variants in HTX in our highly consanguineous population. Twenty-four affected individuals, from 19 unrelated families, were consecutively recruited. Genetic analysis, with exome sequencing, genome sequencing, or multigene panel, detected 9 unique variants, 7 of which were novel, in 8 genes known to be implicated in autosomal recessive form of HTX (C1orf127, CCDC39, CIROP, DNAAF3, DNAH5, DNAH9, MMP21, and MNS1) providing a yield of 42.1%. Of note, 7 of the 9 variants were homozygous, while 2 were inherited in compound heterozygosity, including a heterozygous CNV deletion. A search for candidate genes in negative cases did not reveal a plausible variant. Our work demonstrates a relatively high yield of genetic testing in HTX in a consanguineous population with an enrichment of homozygous variants. The significant genetic heterogeneity observed herewith underscores the complex developmental mechanisms implicated in the pathogenesis of HTX and supports adopting a genome-wide analysis in the diagnostic evaluation of HTX.

Homozygous synonymous FAM111A variant underlies an autosomal recessive form of Kenny-Caffey syndrome.

FAM111A (family with sequence similarity 111 member A) is a serine protease and removes covalent DNA-protein cross-links during DNA replication. Heterozygous gain-of-function variants in FAM111A cause skeletal dysplasias, such as the perinatal lethal osteocraniostenosis and the milder Kenny-Caffey syndrome (KCS). We report two siblings born to consanguineous parents with dysmorphic craniofacial features, postnatal growth retardation, ophthalmologic manifestations, hair and nail anomalies, and skeletal abnormalities such as thickened cortex and stenosis of the medullary cavity of the long bones suggestive of KCS. Using exome sequencing, a homozygous synonymous FAM111A variant, NM_001312909.2:c.81 G > A; p.Pro27=, that affects the last base of the exon and is predicted to alter FAM111A pre-mRNA splicing, was identified in both siblings. We identified aberrantly spliced FAM111A transcripts, reduced FAM111A mRNA levels, and near-complete absence of FAM111A protein in fibroblasts of both patients. After treatment of patient and control fibroblasts with different concentrations of camptothecin that induces covalent DNA-protein cross-links, we observed a tendency towards a reduced proportion of metabolically active cells in patient compared to control fibroblasts. However, under these culture conditions, we did not find consistent and statistically significant differences in cell cycle progression and apoptotic cell death between patient and control cells. Our findings show that FAM111A deficiency underlies an autosomal recessive form of FAM111A-related KCS. Based on our results and published data, we hypothesize that loss of FAM111A and FAM111A protease hyperactivity, as observed for gain-of-function patient-variant proteins, may converge on a similar pathomechanism underlying skeletal dysplasias.

Changes in Upper Airway Space in a Patient with Pycnodysostosis Following Primary Surgery and Orthodontic Treatment: A 12-Year Follow-Up Case Report

Pycnodysostosis (PDS) is an autosomal recessive form of osteosclerotic skeletal dysplasia characterized by craniofacial anomalies, a high-arched palate, and a narrowed pharyngeal space due to mandibular and maxillary deficiencies. These structural anomalies in the upper airway predispose PDS patients to obstructive sleep apnea (OSA). OSA can be managed in PDS patients using either a conservative (non-surgical and multidisciplinary) approach or surgical interventions. Given the craniofacial anomalies associated with PDS, orthodontic treatment aims to address the maxillary transverse deficit and retrognathia. Currently, there is no evidence regarding the impact of orthodontic therapy on OSA levels among PDS patients. This study reports the long-term morphological and functional changes in the upper airway of a PDS patient following adenotonsillectomy and uvulopalatoplasty at an early age (3.6 years) and orthodontic camouflage in late mixed dentition (10 years). Polysomnographies (PSGs), nuclear magnetic resonance (NMR), and lateral cephalograms taken before and after ENT surgery and orthodontic treatment were analyzed. Lateral X-rays were evaluated for changes in the posterior airway space (PAS), while polysomnographies provided the apnea–hypopnea index (AHI). The NMR scans were segmented to measure the perimeter and radius of the upper airway. The findings of this study indicate that improvements following uvulopalatoplasty (UPP) were partial and temporary. Nonetheless, orthodontic therapy and the use of elastics did not appear to influence the PAS or AHI. Future studies with larger cohorts are needed to evaluate the long-term effectiveness of the UPP procedure. This study was conducted in accordance with the CARE guidelines.

DOCK8 deficiency due to a deep intronic variant in two kindreds with hyper-IgE syndrome

Dedicator of cytokinesis 8 (DOCK8) deficiency underlies the majority of cases of patients with autosomal recessive form of the hyper-immunoglobulin E syndrome (HIES). Most DOCK8 mutations involve deletions and splice junction mutations that abrogate protein expression. However, a few patients whose presentation is reminiscent of DOCK8 deficiency have no identifiable mutations. Using Whole Exome Sequencing (WES), we identified a deep intronic homozygous DOCK8 variant located in intron 36 (c.4626 + 76 A > G) in two unrelated patients with features of HIES that resulted in an in-frame 75 base pair intronic sequence insertion in DOCK8 cDNA, resulting in a premature stop codon (p.S1542ins6Ter). This variant resulted in variable decrease in DOCK8 expression that was associated with impaired T cell receptor-triggered actin polymerization, decreased IL-6-induced STAT3 phosphorylation, reduced expression of the Th17 cell markers CCR6 and IL-17, and higher frequencies of GATA3+ T cells indicative of Th2 skewing. Our approach extends the reach of WES in identifying disease-related intronic variants. It highlights the role of non-coding mutations in immunodeficiency disorders, including DOCK8 deficiency, and emphasizes the need to explore these mutations in unexplained inborn errors of immunity.

The Influence of Non-Pharmacological and Pharmacological Interventions on the Course of Autosomal Dominant Polycystic Kidney Disease.

Polycystic kidney disease (PKD) includes autosomal dominant (ADPKD) and autosomal recessive (ARPKD) forms, both of which are primary genetic causes of kidney disease in adults and children. ADPKD is the most common hereditary kidney disease, with a prevalence of 329 cases per million in Europe. This condition accounts for 5-15% of end-stage chronic kidney disease (ESKD) cases, and in developed countries such as Poland, 8-10% of all dialysis patients have ESKD due to ADPKD. The disease is caused by mutations in the PKD1 and PKD2 genes, with PKD1 mutations responsible for 85% of cases, leading to a more aggressive disease course. Recent research suggests that ADPKD involves a metabolic defect contributing to cystic epithelial proliferation and cyst growth. Aim: This review explores the interplay between metabolism, obesity, and ADPKD, discussing dietary and pharmacological strategies that target these metabolic abnormalities to slow disease progression. Conclusion: Metabolic reprogramming therapies, including GLP-1 analogs and dual agonists of GIP/GLP-1 or glucagon/GLP-1 receptors, show promise, though further research is needed to understand their potential in ADPKD treatment fully.

Frequent genetic variants of autosomal recessive non-syndromic forms of inherited retinal diseases in the Russian Federation

Frequent genetic variants of autosomal recessive non-syndromic forms of inherited retinal diseases in the Russian Federation

Phenotypic variability related to dominant UCHL1 mutations: about three families with optic atrophy and ataxia.

Ubiquitin C-terminal hydrolase L1 (UCHL1) has been associated with a severe, complex autosomal recessive spastic paraplegia (HSP79) [1] [2] [3][4]. More recently, UCHL1 loss of function (LoF) variants have been associated to an autosomal dominant disease characterized by late-onset spastic ataxia, neuropathy, and frequent optic atrophy [5]. Routine clinical care whole-genome (WGS) and exome (ES) sequencing. We present three families with autosomal dominant UCHL1-related disorder. The clinical phenotype mainly associated optic atrophy, mixed cerebellar and sensory ataxia, and possible hearing loss. We delineated two major phenotypes, even within the same family: (1) juvenile severe optic atrophy followed by a later-onset ataxia, or (2) late-onset ataxia with asymptomatic or mild optic atrophy. The families harboured three novel heterozygous variants in UCHL1: two loss of function (p.Lys115AsnfsTer40; c.171_174 + 7del11), and one missense (p.Asp176Asn) involving the catalytic site of the protein and potentially altering the adjacent splice site. We confirm the existence of dominantly inherited UCHL1 pathogenic variants. We describe a considerable intrafamilial phenotypic variability, with two main phenotypes. Optic atrophy was consistently present, but with varying degrees of severity. Neither delayed motor or intellectual development, nor dysmorphic features were part of the dominant phenotype in comparison with the autosomal recessive form. The molecular mechanism appears to be haploinsufficiency. UCHL1 monoallelic variants should therefore be considered in any case of early-onset optic atrophy or in late-onset complex ataxic syndrome with asymptomatic optic atrophy.

Clinical and genetic delineation of autosomal recessive and dominant ACTL6B-related developmental brain disorders

PurposeThis study aims to comprehensively delineate the phenotypic spectrum of ACTL6B-related disorders, previously associated with both autosomal recessive and autosomal dominant neurodevelopmental disorders. Molecularly, the role of the nucleolar protein ACTL6B in contributing to the disease has remained unclear. MethodsWe identified 105 affected individuals, including 39 previously reported cases, and systematically analyzed detailed clinical and genetic data for all individuals. Additionally, we conducted knockdown experiments in neuronal cells to investigate the role of ACTL6B in ribosome biogenesis. ResultsBiallelic variants in ACTL6B are associated with severe-to-profound global developmental delay/intellectual disability, infantile intractable seizures, absent speech, autistic features, dystonia, and increased lethality. De novo monoallelic variants result in moderate-to-severe global developmental delay/intellectual disability, absent speech, and autistic features, whereas seizures and dystonia were less frequently observed. Dysmorphic facial features and brain abnormalities, including hypoplastic corpus callosum, and parenchymal volume loss/atrophy, are common findings in both groups. We reveal that in the nucleolus, ACTL6B plays a crucial role in ribosome biogenesis, particularly in pre-rRNA processing. ConclusionThis study provides a comprehensive characterization of the clinical spectrum of both autosomal recessive and dominant forms of ACTL6B-associated disorders. It offers a comparative analysis of their respective phenotypes provides a plausible molecular explanation and suggests their inclusion within the expanding category of “ribosomopathies.”

Phenotypic Variability of LGMD 2C/R5 in a Genetically Homogenous Group of Bulgarian Muslim Roma.

Sarcoglycanopathies are among the most frequent and severe forms of autosomal recessive forms of limb-girdle muscular dystrophies (LGMDs) with childhood onset. Four subtypes are known: LGMDR3, LGMDR4, LGMDR5 and LGMDR6, which are caused, respectively, by mutations in the SGCA, SGCB, SGCG and SGCD genes. We present the clinical variability of LGMD 2C/R5 among a genetically homogeneous group of 57 patients, belonging to 35 pedigrees. Molecular genetic analysis showed that all 57 patients were homozygous for the C283Y variant. The muscles of the pelvic girdle and the trunk were affected early and were more severely affected, followed by the shoulder girdle. Macroglossia, hypertrophy of the calves, scapular winging and lumbar hyperlordosis were common in the ambulatory phase. A great intra and interfamilial variability in the clinical presentation of LGMD 2C/R5 was observed, despite having the same underlying molecular defect. Females demonstrated a relatively milder clinical course compared to males. Mean creatine phosphokinase (CK) CK levels were 20 times above normal values. Muscle computer tomography (CT) CT or MRIs showed earlier and more severe involvement of the flexor proximal limb muscles in comparison to extensor muscles.

Single Mutation different Clinical Findings: IGLL1 Defect

Agammaglobulinemia is a rare inherited immunodeficiency disorder characterized by low or absent B cells with absent immunoglobulins. While X-linked agammaglobulinemia (XLA) is the most common type other genetic forms of agammaglobulinemia have been identified. During early childhood, passively transferred maternal Immunoglobulin G protects against various infections. The depletion of these antibodies begins between 6 and 12 months of age, resulting in recurrent sinusitis, bronchitis, and pneumonia in children with X-linked agammaglobulinemia. However, less common autosomal recessive forms of agammaglobulinemia present with more severe clinical features, leading to earlier diagnosis. Herein we present the case of a two-month-old male with IGLL1 gene defect and different clinical findings of family members with the same mutation.

Naturally occurring hyperactive variants of human parkin.

Parkinson's disease (PD) is the second most common neurodegenerative disease in the world. Although most cases are sporadic and occur later in life, 10-15% of cases are genetic. Loss-of-function mutations in the ring-between-ring E3 ubiquitin ligase parkin, encoded by the PRKN gene, cause autosomal recessive forms of early onset PD. Together with the kinase PINK1, parkin forms a mitochondrial quality control pathway that tags damaged mitochondria for clearance. Under basal conditions, parkin is inhibited and compounds that increase its activity have been proposed as a therapy for PD. Recently, several naturally occurring hyperactive parkin variants were identified, which increased mitophagy in cultured cells. Here, we validate the hyperactivities of these variants in vitro and compare the levels of activity of the variants to those of the wild-type and the well-characterized hyperactive variant, W403A. We also study the effects of mutating the parkin ACT (activating element) on parkin activity in vitro. This work advances our understanding of the pathogenicity of parkin variants and is an important first step in the design of molecules to increase parkin activity.

Loss of the long form of Plod2 phenocopies contractures of Bruck syndrome-osteogenesis imperfecta.

Bruck syndrome is an autosomal recessive form of osteogenesis imperfecta caused by biallelic variants in PLOD2 or FKBP10 and is characterized by joint contractures, bone fragility, short stature, and scoliosis. PLOD2 encodes LH2, which hydroxylates type I collagen telopeptide lysines, a critical step for collagen crosslinking. The Plod2 global knockout mouse model is limited by early embryonic lethality, and thus, the role of PLOD2 in skeletogenesis is not well understood. We generated a novel Plod2 mouse line modeling a variant identified in two unrelated individuals with Bruck syndrome: PLOD2 c.1559dupC, predicting a frameshift and loss of the long isoform LH2b. In the mouse, the duplication led to loss of LH2b mRNA as well as significantly reduced total LH2 protein. This model, Plod2fs/fs, survived up to E18.5 although in non-Mendelian genotype frequencies. The homozygous frameshift model recapitulated the joint contractures seen in Bruck syndrome and had indications of absent type I collagen telopeptide lysine hydroxylation in bone. Genetically labeling tendons with Scleraxis-GFP in Plod2fs/fs mice revealed the loss of extensor tendons in the forelimb by E18.5, and developmental studies showed extensor tendons developed through E14.5 but were absent starting at E16.5. Second harmonic generation showed abnormal tendon type I collagen fiber organization, suggesting structurally abnormal tendons. Characterization of the skeleton by μCT and Raman spectroscopy showed normal bone mineralization levels. This work highlights the importance of properly crosslinked type I collagen in tendon and bone, providing a promising new mouse model to further our understanding of Bruck syndrome.

Precision Dopaminergic Treatment in a Cohort of Parkinson's Disease Patients Carrying Autosomal Recessive Gene Variants: Clinical Cohort Data and a Mini Review.

Parkinson's disease (PD) patients harboring recessive gene variants exhibit a distinct clinical phenotype with an early disease onset and relatively mild symptoms. Data concerning individualized therapy for autosomal recessive PD forms are still scarce. Demographic and treatment data of a cohort of PD carriers of recessive genes (nine homozygous or compound heterozygous PRKN carriers, four heterozygous PRKN carriers, and three biallelic PINK1 carriers) were evaluated. The average levodopa equivalent daily dose (LEDD) was 806.8 ± 453.5 (range 152-1810) in PRKN carriers and 765 ± 96.6 (range 660-850) in PINK1 carriers. The majority responded to low/moderate doses of levodopa. The response to dopamine agonists (DAs) was often favorable both as initial and longitudinal therapy. In total, 8/13 PRKN and 1/3 PINK1 carriers were treated with amantadine successfully, and this also applied to patients who could not tolerate levodopa or DAs. In the era of personalized treatment, the therapeutic approach in recessive PD gene carriers might differ as compared to idiopathic PD. Lower LEDD doses were efficient even in patients with a very long disease duration, while a few patients were doing well without any levodopa treatment decades after disease initiation. DAs or amantadine could be used as a first and main line treatment regimen if well tolerated. Literature data on therapeutic strategies in carriers of pathogenic mutations in recessive PD genes, including device-aided treatments, will be further discussed.

A nonsense variant in KRT31 is associated with autosomal-dominant monilethrix.

Monilethrix is a rare hereditary hair disorder that is characterised by a beaded hair shaft structure and increased hair fragility. Patients may also present with keratosis pilaris and nail changes. Research has identified three genes for autosomal-dominant monilethrix (KRT81, KRT83, and KRT86), and one gene for the autosomal-recessive form (DSG4). To investigate the genetic basis of autosomal-dominant monilethrix in families with no pathogenic variants in any of the known monilethrix genes, and to understand the mechanistic basis of variant pathogenicity using a cellular model. Nine affected individuals from four unrelated families were included in this study. A clinical diagnosis of monilethrix was assigned based on clinical examination and/or trichoscopy. Exome sequencing (ES) was performed in six individuals to identify pathogenic variants, and Sanger sequencing was used for co-segregation and haplotype analyses. Cell culture experiments (immunoblotting, immunofluorescence, and reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) analyses) were used to confirm variant pathogenicity, to determine expression and subcellular localisation of proteins, and to identify a possible nonsense-mediated mRNA decay. In six affected individuals with clinically suggested monilethrix, ES led to the identification of the nonsense variant c.1081G>T; p.(Glu361*) in KRT31, which was subsequently identified in other affected members of these families by Sanger sequencing. This variant led to the abolition of both the last three amino acids of the 2B subdomain and the complete C-terminal tail domain of keratin 31. Immunoblotting demonstrated that when co-expressed with its binding partner keratin 85, the truncated keratin 31 was still expressed, albeit less abundantly than the wild type protein. Immunofluorescence revealed that p.(Glu361*) keratin 31 had an altered cytoskeletal localisation and formed vesicular-like structures in the cell cytoplasm near the cell membrane. RT-qPCR analysis did not generate evidence for a nonsense mediated decay of the mutant transcript. This study is the first to identify pathogenic variants in KRT31 as a cause of autosomal-dominant monilethrix. This highlights the importance of hair keratin proteins in hair biology, and will increase the molecular diagnostic yield for rare ectodermal phenotypes of hair and nail tissues.

A novel homozygous FAM92A gene (CIBAR1) variant further confirms its association with non-syndromic postaxial polydactyly type A9 (PAPA9).

Polydactyly is a very common digit anomaly, having extra digits in hands and/or toes. Non-syndromic polydactyly in both autosomal dominant and autosomal recessive forms are caused by disease-causing variants in several genes, including GLI1, GLI3, ZNF141, FAM92A, IQCE, KIAA0825, MIPOL1, STKLD1, PITX1, and DACH1. Whole exome sequencing (WES) followed by bi-directional Sanger sequencing was performed for the single affected individual (II-1) of the family to reveal the disease causative variant/gene. 3D protein modeling and structural molecular docking was performed to determine the effect of the identified mutation on the overall protein structure. WES revealed a novel biallelic missense variant (c.472G>C; p.Ala158Pro) in exon 6 of the FAM92A gene. The identified variant segregated perfectly with the disease phenotype using Sanger sequencing. Furthermore, Insilco analysis revealed that the variant significantly changes the protein secondary structure, and substantially impact the stability of FAM92A. We report the second FAM92A disease-causing mutation associated with recessive non-syndromic postaxial polydactyly. The data further confirms the contribution of FAM92A in limb development and patterning.

Quantitative correlation of ENPP1 pathogenic variants with disease phenotype

Ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) codes for a type 2 transmembrane glycoprotein which hydrolyzes extracellular phosphoanhydrides into bio-active molecules that regulate, inter alia, ectopic mineralization, bone formation, vascular endothelial proliferation, and the innate immune response. The clinical phenotypes produced by ENPP1 deficiency are disparate, ranging from life-threatening arterial calcifications to cutaneous hypopigmentation. To investigate associations between disease phenotype and enzyme activity we quantified the enzyme velocities of 29 unique ENPP1 pathogenic variants in 41 patients enrolled in an NIH study along with 33 other variants reported in literature. We correlated the relative enzyme velocities with the presenting clinical diagnoses, performing the catalytic velocity measurements simultaneously in triplicate using a high-throughput assay to reduce experimental variation. We found that ENPP1 variants associated with autosomal dominant phenotypes reduced enzyme velocities by 50 % or more, whereas variants associated with insulin resistance had non-significant effects on enzyme velocity. In Cole disease the catalytic velocities of ENPP1 variants associated with AD forms trended to lower values than those associated with autosomal recessive forms – 8-32 % vs. 33 % of WT, respectively. Additionally, ENPP1 variants leading to life-threatening vascular calcifications in GACI patients had widely variable enzyme activities, ranging from no significant differences compared to WT to the complete abolishment of enzyme velocity. Finally, disease severity in GACI did not correlate with the mean enzyme velocity of the variants present in affected compound heterozygotes but did correlate with the more severely damaging variant. In summary, correlation of ENPP1 enzyme velocity with disease phenotypes demonstrate that enzyme velocities below 50 % of WT levels are likely to occur in the context of autosomal dominant disease (due to a monoallelic variant), and that disease severity in GACI infants correlates with the more severely damaging ENPP1 variant in compound heterozygotes, not the mean velocity of the pathogenic variants present.

Sex differences in amino acid composition in a rodent model of ARPKD, the PCK rat

Polycystic Kidney Disease (PKD) is a severe, genetically inherited disease that leads to renal failure. Like several other chronic kidney diseases, male sex is a risk factor for accelerated PKD. Rat models of both Autosomal Recessive and Dominant forms of PKD (PCK and Han:SPRD rats, respectively) exhibit sex differences in disease progression. Previous studies have found that amino acids (AAs) and peptides are predominant constituents of cystic fluid. We hypothesized that AA homeostasis in male and female cystic fluid would demonstrate sexual dimorphism, and these differences may provide essential information about the progression of cystogenesis. We quantified the AAs in cystic fluid, plasma, and urine in PCK and control Sprague Dawley (SD) rats (only plasma and urine for SD rats). Of the 42 AAs that were measured, only asparagine, serine, aspartic acid, glutamic acid, beta-alanine, cystathionine, and leucine were NOT significantly different between SD and PCK plasma values. Interestingly, only 18 AAs were significantly different in urine of PCK rats compared to SD rats. In SD rats, between sexes, 26 AAs were significantly different in plasma and 5 were significantly different in urine. Among PCK rats, 13 AAs in plasma, 9 AAs in urine, and 4 AAs in cystic fluid were significantly different between sexes. The 4 AAs that differed between male and female cystic fluid were 1-methylhistidine, 3-methylhistidine, ethanolamine, and taurine. Moreover, taurine was the most abundant AA in cystic fluid. Taurine concentrations in both plasma (165 ± 9 vs. 128 ± 4 μM, N=6, p=0.003) and cystic fluid (7508 ± 469 vs. 4557 ± 788 μM, N=6, p=0.01) were significantly different between sexes in the PCK rats (male vs. female, respectively). Urine values for the PCK rats (9705 ± 1863 vs. 7570 ± 1631 μM, N=6) were not significantly different in males and females; however, the average urinary taurine excretion in PCK rats was nearly 4-fold greater than SD rats (8637 ± 1223 vs. 2219 ± 465 μM, N=12, p<0.0001). There were no significant differences in taurine concentrations between SD male and female rat plasma (202 ± 17 vs. 194 ± 7.0 μM, N=6) or urine (2044 ± 614 vs. 2395 ± 752 μM, N=6). Western blot of the taurine transporter, TauT, detected bands at 50 and 75 kDa, and both bands were significantly reduced by ~50% in PCK kidneys compared to SD kidneys. Lastly, immunolabeling in PCK kidney sections demonstrated that TauT is present at the apical membrane of cyst epithelia. These results point to a potential role for AAs, and specifically for taurine in cystogenesis, which likely varies by sex in diseased, but not healthy kidneys. R00 HL153686, BX004024, R01 DK126720, R01 DK129227. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Osteopetrosis and related osteoclast disorders in adults: A review and knowledge gaps On behalf of the European calcified tissue society and ERN BOND

Osteopetrosis refers to a group of related rare bone diseases characterized by a high bone mass due to impaired bone resorption by osteoclasts. Despite the high bone mass, skeletal strength is compromised and the risk of fracture is high, particularly in the long bones. Osteopetrosis was classically categorized by inheritance pattern into autosomal recessive forms (ARO), which are severe and diagnosed within the first years of life, an intermediate form and an autosomal dominant (ADO) form; the latter with variable clinical severity and typically diagnosed during adolescence or in young adulthood. Subsequently, the AD form was shown to be a result of mutations in the gene CLCN7 encoding for the ClC-7 chloride channel). Traditionally, the diagnosis of osteopetrosis was made on radiograph appearance alone, but recent molecular and genetic advances have enabled a greater fidelity in classification of osteopetrosis subtypes. In the more severe ARO forms (e.g., malignant infantile osteopetrosis MIOP) typical clinical features have severe consequences and often result in death in early childhood. Major complications of ADO are atypical fractures with delay or failure of repair and challenge in orthopedic management. Bone marrow failure, dental abscess, deafness and visual loss are often underestimated and neglected in relation with lack of awareness and expertise. Accordingly, the care of adult patients with osteopetrosis requires a multidisciplinary approach ideally in specialized centers. Apart from hematopoietic stem cell transplantation in certain infantile forms, the treatment of patients with osteopetrosis, has not been standardized and remains supportive. Further clinical studies are needed to improve our knowledge of the natural history, optimum management and impact of osteopetrosis on the lives of patients living with the disorder.

Compound heterozygous mutations in three Chinese patients of Segawa syndrome and their treatment outcomes.

Segawa syndrome is a rare autosomal recessive form of dopa-responsive dystonia resulting from TH gene dysfunction. Patients typically exhibit symptoms such as generalized dystonia, rigidity, tremors, infantile Parkinsonism, and pseudo-spastic paraplegia. Levodopa is often an effective treatment. Due to its rarity, high heterogeneity, and poorly understood pathological mutation and phenotype spectrums, as well as genotype-phenotype and genotype-treatment outcome correlations, Segawa syndrome poses diagnostic and therapeutic challenges. In our study, through clinical and molecular analyses of three Chinese Segawa patients, we re-evaluated the pathogenicity of a TH mutation (c.880G>C;p.G294R) previously categorized as "Conflicting classifications of pathogenicity" in ClinVar. Also, we summarized the clinical phenotypes of all reported Segawa syndrome cases until 2023 and compared them with our patients. We identified a novel phenotype, "cafe-au-lait macules," not previously observed in Segawa patients. Additionally, we discussed the correlation between specific genotypes and phenotypes, as well as genotypes and treatment outcomes of our three cases. Our findings aim to enhance the understanding of Segawa syndrome, contributing to improved diagnosis and treatment approaches in the future.

Association of Antenatal Evaluations with Postmortem and Genetic Findings in the Series of Fetal Osteogenesis Imperfecta

Introduction: Counseling osteogenesis imperfecta (OI) pregnancies is challenging due to the wide range of onsets and clinical severities, from perinatal lethality to milder forms detected later in life. Methods: Thirty-eight individuals from 36 families were diagnosed with OI through prenatal ultrasonography and/or postmortem clinical and radiographic findings. Genetic analysis was conducted on 26 genes associated with OI in these subjects that emerged over the past 20 years; while some genes were examined progressively, all 26 genes were examined in the group where no pathogenic variations were detected. Results: Prenatal and postnatal observations both consistently showed short limbs in 97%, followed by bowing of the long bones in 89%. Among 32 evaluated cases, all exhibited cranial hypomineralization. Fractures were found in 29 (76%) cases, with multiple bones involved in 18 of them. Genetic associations were disclosed in 27 families with 22 (81%) autosomal dominant and five (19%) autosomal recessive forms, revealing 25 variants in six genes (COL1A1, COL1A2, CREB3L1, P3H1, FKBP10, and IFITM5), including nine novels. Postmortem radiological examination showed variability in intrafamily expression of CREBL3- and P3H1-related OI. Conclusion: Prenatal diagnosis for distinguishing OI and its subtypes relies on factors such as family history, timing, ultrasound, genetics, and postmortem evaluation.