The pathogenic mechanism of syndactyly type V identified in a Hoxd13Q50R knock-in mice.

Syndactyly type V (SDTY5) is an autosomal dominant extremity malformation characterized by fusion of the fourth and fifth metacarpals. In the previous publication, we first identified a heterozygous missense mutation Q50R in homeobox domain (HD) of HOXD13 in a large Chinese family with SDTY5. In order to substantiate the pathogenicity of the variant and elucidate the underlying pathogenic mechanism causing limb malformation, transcription-activator-like effector nucleases (TALEN) was employed to generate a Hoxd13Q50R mutant mouse. The mutant mice exhibited obvious limb malformations including slight brachydactyly and partial syndactyly between digits 2-4 in the heterozygotes, and severe syndactyly, brachydactyly and polydactyly in homozygotes. Focusing on BMP2 and SHH/GREM1/AER-FGF epithelial mesenchymal (e-m) feedback, a crucial signal pathway for limb development, we found the ectopically expressed Shh, Grem1 and Fgf8 and down-regulated Bmp2 in the embryonic limb bud at E10.5 to E12.5. A transcriptome sequencing analysis was conducted on limb buds (LBs) at E11.5, revealing 31 genes that exhibited notable disparities in mRNA level between the Hoxd13Q50R homozygotes and the wild-type. These genes are known to be involved in various processes such as limb development, cell proliferation, migration, and apoptosis. Our findings indicate that the ectopic expression of Shh and Fgf8, in conjunction with the down-regulation of Bmp2, results in a failure of patterning along both the anterior-posterior and proximal-distal axes, as well as a decrease in interdigital programmed cell death (PCD). This cascade ultimately leads to the development of syndactyly and brachydactyly in heterozygous mice, and severe limb malformations in homozygous mice. These findings suggest that abnormal expression of SHH, FGF8, and BMP2 induced by HOXD13Q50R may be responsible for the manifestation of human SDTY5.

[Genetic analysis of a Chinese pedigree affected with Brachydactyly type B1 due to a novel variant of ROR2 gene].

OBJECTIVE: To explore the genetic basis for a Chinese pedigree affected with Brachydactyly type B1 (BDB1) through whole exome sequencing (WES). METHODS: A BDB1 pedigree admitted to the Affiliated Women and Children's Hospital of Qingdao University on June 25, 2021 was selected as the study subject. Clinical data of the pedigree was collected with informed consent. WES was carried out for the proband, and candidate variant was verified by Sanger sequencing and bioinformatic analysis. RESULTS: WES and Sanger sequencing had identified a heterozygous c.2257delT variant in the ROR2 gene of the proband and his affected father, which has conformed to an autosomal dominant pattern of inheritance. Based on the guidelines from the American College of Medical Genetics and Genomics (ACMG), the variant was classified to be likely pathogenic (PVS1_Strong+PM2 Supporting+PP4). CONCLUSION: The c.2257delT variant of the ROR2 gene was unreported previously and is strongly correlated with the BDB1-like phenotype in this pedigree. Above finding has enriched the mutational spectrum of the ROR2 gene and facilitated the diagnosis and genetic counseling for this pedigree.

Suppression of apoptosis impairs phalangeal joint formation in the pathogenesis of brachydactyly type A1.

Apoptosis occurs during development when a separation of tissues is needed. Synovial joint formation is initiated at the presumptive site (interzone) within a cartilage anlagen, with changes in cellular differentiation leading to cavitation and tissue separation. Apoptosis has been detected in phalangeal joints during development, but its role and regulation have not been defined. Here, we use a mouse model of brachydactyly type A1 (BDA1) with an IhhE95K mutation, to show that a missing middle phalangeal bone is due to the failure of the developing joint to cavitate, associated with reduced apoptosis, and a joint is not formed. We showed an intricate relationship between IHH and interacting partners, CDON and GAS1, in the interzone that regulates apoptosis. We propose a model in which CDON/GAS1 may act as dependence receptors in this context. Normally, the IHH level is low at the center of the interzone, enabling the "ligand-free" CDON/GAS1 to activate cell death for cavitation. In BDA1, a high concentration of IHH suppresses apoptosis. Our findings provided new insights into the role of IHH and CDON in joint formation, with relevance to hedgehog signaling in developmental biology and diseases.

ADAM19 cleaves the PTH receptor and associates with brachydactyly type E.

Brachydactyly type E (BDE), shortened metacarpals, metatarsals, cone-shaped epiphyses, and short stature commonly occurs as a sole phenotype. Parathyroid hormone-like protein (PTHrP) has been shown to be responsible in all forms to date, either directly or indirectly. We used linkage and then whole genome sequencing in a small pedigree, to elucidate BDE and identified a truncated disintegrin-and-metalloproteinase-19 (ADAM19) allele in all affected family members, but not in nonaffected persons. Since we had shown earlier that the extracellular domain of the parathyroid hormone receptor (PTHR1) is subject to an unidentified metalloproteinase cleavage, we tested the hypothesis that ADAM19 is a sheddase for PTHR1. WT ADAM19 cleaved PTHR1, while mutated ADAM-19 did not. We mapped the cleavage site that we verified with mass spectrometry between amino acids 64-65. ADAM-19 cleavage increased Gq and decreased Gs activation. Moreover, perturbed PTHR1 cleavage by ADAM19 increased ß-arrestin2 recruitment, while cAMP accumulation was not altered. We suggest that ADAM19 serves as a regulatory element for PTHR1 and could be responsible for BDE. This sheddase may affect other PTHrP or PTH-related functions.

A novel heterozygous mutation in PTHLH causing autosomal dominant brachydactyly type E complicated with short stature.

BACKGROUND: Brachydactyly type E (BDE) is a general term characterized by variable shortening of metacarpals and metatarsals, with phalanges affected frequently. It can occur as an isolated form or part of syndromes and manifest a high degree of phenotypic variability. In this study, we have identified the clinical characteristics and pathogenic causes of a four-generation pedigree with 10 members affected by BDE and short stature. METHODS: After the informed consent was signed, clinical data and peripheral blood samples were collected from available family members. Karyotype analysis, array-CGH, next-generation sequencing, and Sanger sequencing were employed to identity the pathogenic candidate gene. RESULTS: No translocation or microdeletion/duplication was found in karyotype analysis and array-CGH; hence, a novel heterozygous mutation, c.146dupA. p.S50Vfs*22, was detected by next-generation sequencing in PTHLH gene, leading to a premature stop codon. Subsequently, the mutation was confirmed by Sanger sequencing and co-segregation analysis. CONCLUSION: In this study, we described a novel heterozygous mutation (c.146dupA. p.S50Vfs*22) of gene PTHLH in a Chinese family. The mutation could induce a premature stop codon leading to a truncation of the protein. Our study broadened the mutation spectrum of PTHLH in BDE.

Reversal of cardiac and renal damage in a teenager with hypertension: A case report.

The authors describe the case of a 16-year-old male who was incidentally found to have a blood pressure of 200/? mmHg 6 months previously due to blurred vision and was diagnosed with "high risk of hypertension grade 3, renal insufficiency, hypertensive encephalopathy, hypertensive heart disease, and fundus hemorrhage" after relevant examinations were performed. His blood pressure fluctuated around 120/90 mmHg after beginning antihypertensive treatment. While the diagnostic work-up of his hypertension was inconclusive, he had severe hypertension with brachydactyly type E and short stature on physical examination. The patient's cardiac damage and renal insufficiency ultimately returned to normal after strict blood pressure control, suggesting that hypertension and brachydactyly syndrome alone do not cause cardiac and renal damage.

RUNX2-related metaphyseal dysplasia with maxillary hypoplasia: A rare skeletal disorder resembling SFRP4-related Pyle disease.

Metaphyseal dysplasia with maxillary hypoplasia with or without brachydactyly (MDMHB) is an ultra-rare skeletal dysplasia caused by heterozygous intragenic RUNX2 duplications, comprising either exons 3 to 5 or exons 3 to 6 of RUNX2. In this study, we describe a 14-year-old Belgian boy with metaphyseal dysplasia with maxillary hypoplasia but without brachydactyly. Clinical and radiographic examination revealed mild facial dysmorphism, dental anomalies, enlarged clavicles, genua valga and metaphyseal flaring and thin cortices with an osteoporotic skeletal appearance. Exome sequencing led to the identification of a de novo heterozygous tandem duplication within RUNX2, encompassing exons 3 to 7. This duplication is larger than the ones previously reported in MDMHB cases since it extends into the C-terminal activation domain of RUNX2. We review previously reported cases with MDMHB and highlight the resemblance of this disorder with Pyle disease, which may be explained by intersecting molecular pathways between RUNX2 and sFRP4. This study expands our knowledge on the genotypic and phenotypic characteristics of MDMHB and the role of RUNX2 in rare bone disorders.

Challenges in Diagnosing Fibrodysplasia Ossificans Progressiva: A Case Report.

CASE: A 5-year-old boy presented with multiple bony swellings in the dorsal spine region, restricted left shoulder movement, and a previous misdiagnosis of hereditary multiple exostoses (HMEs) resulting in unnecessary excision of the right scapular lesion. Clinical examination revealed hallux valgus, brachydactyly, and limited neck movement. Radiography and computed tomography confirmed a diagnosis of fibrodysplasia ossificans progressiva (FOP). CONCLUSION: This case report underscores the importance of accurate diagnosis and differentiation between FOP and HME. Hallux valgus, brachydactyly, and restricted neck movement suggested FOP. It is paramount for orthopaedic surgeons to exclude rare disorders before performing any interventions. Biopsies or resections of bone formation areas should be avoided for patients with FOP.

Genotype-Phenotype Correlations in 2q37-Deletion Syndrome: An Update of the Clinical Spectrum and Literature Review.

2q37 microdeletion/deletion syndrome (2q37DS) is one of the most common subtelomeric deletion disorders, caused by a 2q37 deletion of variable size. The syndrome is characterized by a broad and diverse spectrum of clinical findings: characteristic facial dysmorphism, developmental delay/intellectual disability (ID), brachydactyly type E, short stature, obesity, hypotonia in infancy, and abnormal behavior with autism spectrum disorder. Although numerous cases have been described so far, the exact mapping of the genotype and phenotype have not yet been achieved. MATERIALS AND METHODS: In this study we analyzed nine newly diagnosed cases with 2q37 deletion (3 male/6 female, aged between 2 and 30 years old), and followed up at the Iasi Regional Medical Genetics Centre. All patients were tested first with MLPA using combined kits P036/P070 subtelomeric screening mix and follow-up mix P264; after, the deletion size and location were confirmed via CGH-array. We compared our findings with the data of other cases reported in the literature. RESULTS: From nine cases, four had pure 2q37 deletions of variable sizes, and five presented deletion/duplication rearrangements (with chromosomes 2q, 9q, and 11p). In most cases, characteristic phenotypic aspects were observed: 9/9 facial dysmorphism, 8/9 global developmental delay and ID, 6/9 hypotonia, 5/9 behavior disorders, and 8/9 skeletal anomalies-especially brachydactyly type E. Two cases had obesity, one case had craniosynostosis, and four had heart defects. Other features found in our cases included translucent skin and telangiectasias (6/9), and a hump of fat on the upper thorax (5/9). CONCLUSIONS: Our study enriches the literature data by describing new clinical features associated with 2q37 deletion, and possible genotype-phenotype correlations.

Natural history of clinical features in two brothers with acromesomelic dysplasia related to PRKG2.

Acromesomelic dysplasias (AMD) are a group of skeletal dysplasia characterized by shortening of the middle and distal segments of the limbs. Recently, biallelic PRKG2 variants have been reported to cause a new type of AMD. We detected biallelic novel variant (c.1635-1G > C) in PRKG2 in two brothers with mild to severe short stature, short limbs, cubitus varus, and brachydactyly. Radiological examination showed platyspondyly with anterior beaking of the vertebral bodies, stubby long bones with metaphyseal flaring and moderate brachydactyly with cone-shaped epiphyses of the middle and proximal phalanges. Upper limb proportions of the older brother were clinically classified as rhizomelic, however radiologic findings supported acromesomelia, along with the elbow limitation. Annual follow-ups of the older brother from the age of 5 to 20 years revealed progression of short stature with age but platyspondyly and anterior beaking became less conspicuous. The younger brother showed milder short stature and less conspicuous disproportion of the limbs than those of the older brother; however, platyspondyly and anterior beaking were more prominent on the radiographs obtained at the same age. In conclusion, this report provides new insights into the natural history of AMD type PRKG2 confirming the intrafamilial heterogeneity.

Biallelic PRMT7 pathogenic variants are associated with a recognizable syndromic neurodevelopmental disorder with short stature, obesity, and craniofacial and digital abnormalities.

PURPOSE: Protein arginine methyltransferase 7 (PRMT7) is a member of a family of enzymes that catalyzes the methylation of arginine residues on several protein substrates. Biallelic pathogenic PRMT7 variants have previously been associated with a syndromic neurodevelopmental disorder characterized by short stature, brachydactyly, intellectual developmental disability, and seizures. To our knowledge, no comprehensive study describes the detailed clinical characteristics of this syndrome. Thus, we aim to delineate the phenotypic spectrum of PRMT7-related disorder. METHODS: We assembled a cohort of 51 affected individuals from 39 different families, gathering clinical information from 36 newly described affected individuals and reviewing data of 15 individuals from the literature. RESULTS: The main clinical characteristics of the PRMT7-related syndrome are short stature, mild to severe developmental delay/intellectual disability, hypotonia, brachydactyly, and distinct facial morphology, including bifrontal narrowing, prominent supraorbital ridges, sparse eyebrows, short nose with full/broad nasal tip, thin upper lip, full and everted lower lip, and a prominent or squared-off jaw. Additional variable findings include seizures, obesity, nonspecific magnetic resonance imaging abnormalities, eye abnormalities (i.e., strabismus or nystagmus), and hearing loss. CONCLUSION: This study further delineates and expands the molecular, phenotypic spectrum and natural history of PRMT7-related syndrome characterized by a neurodevelopmental disorder with skeletal, growth, and endocrine abnormalities.

ERI1: A case report of an autosomal recessive syndrome associated with developmental delay and distal limb abnormalities.

ERI1 is an evolutionary conserved 3'-5' exonuclease with an important function in multiple RNA processing pathways. Although the molecular mechanisms in which ERI1 is involved have been studied extensively in model organisms, the pathology associated with ERI1 variants in humans has remained elusive because no case has been reported so far. Here, we present a case of a female patient with a homozygous nonsense variant in ERI1 gene. The patient exhibits mild intellectual disability, eyelid ptosis, and anomalies in her hands and feet (brachydactyly, clinodactyly, dysplastic/short nail of halluces, brachytelephalangy, short metacarpals, and toe syndactyly). This case report is the first of its kind and is invaluable for understanding ERI1 pathology in humans.

Genotype-Phenotype Correlation of Distal 2q37 Deletions.

Brachydactyly mental retardation syndrome (BDMR) typically results from large deletions (>2-9 Mb) in distal 2q37. Haploinsufficiency of HDAC4 with incomplete penetrance has been proposed as the primary genetic cause of BDMR. To date, pure 2q37 deletions distal to HDAC4 were reported only in a limited number of individuals who share a subset of the clinical manifestations seen in cases with 2q37 deletions encompassing HDAC4. Here, we present a 4-year-old African American male who carries the smallest established 2q37.3 deletion distal to HDAC4 (827.1 kb; 16 OMIM genes). His clinical features that overlap with BDMR phenotypes include expressive-receptive language delay, behavioral issues, mild facial dysmorphism such as frontal bossing, and bilateral 5th finger brachydactyly and clinodactyly. The deletion was inherited from his mother with a history of learning difficulties and similar facial dysmorphism. This case provides important genotype-phenotype correlation information and suggests a 2q37 region distal to HDAC4 encompassing the HDLBP gene may contribute to a subset of clinical features overlapping with those seen in individuals with BDMR.

A novel variant in the ROR2 gene underlying brachydactyly type B: a case report.

BACKGROUND: Brachydactyly type B is an autosomal dominant disorder that is characterized by hypoplasia of the distal phalanges and nails and can be divided into brachydactyly type B1 (BDB1) and brachydactyly type B2 (BDB2). BDB1 is the most severe form of brachydactyly and is caused by truncating variants in the receptor tyrosine kinase-like orphan receptor 2 (ROR2) gene. CASE PRESENTATION: Here, we report a five-generation Chinese family with brachydactyly with or without syndactyly. The proband and her mother underwent digital separation in syndactyly, and the genetic analyses of the proband and her parents were provided. The novel heterozygous frameshift variant c.1320dupG, p.(Arg441Alafs*18) in the ROR2 gene was identified in the affected individuals by whole-exome sequencing and Sanger sequencing. The c.1320dupG variant in ROR2 is predicted to produce a truncated protein that lacks tyrosine kinase and serine/threonine- and proline-rich structures and remarkably alters the tertiary structures of the mutant ROR2 protein. CONCLUSION: The c.1320dupG, p.(Arg441Alafs*18) variant in the ROR2 gene has not been reported in any databases thus far and therefore is novel. Our study extends the gene variant spectrum of brachydactyly and may provide information for the genetic counselling of family members.

The molecular genetics of human appendicular skeleton.

Disorders that result from de-arrangement of growth, development and/or differentiation of the appendages (limbs and digit) are collectively called as inherited abnormalities of human appendicular skeleton. The bones of appendicular skeleton have central role in locomotion and movement. The different types of appendicular skeletal abnormalities are well described in the report of "Nosology and Classification of Genetic skeletal disorders: 2019 Revision". In the current article, we intend to present the embryology, developmental pathways, disorders and the molecular genetics of the appendicular skeletal malformations. We mainly focused on the polydactyly, syndactyly, brachydactyly, split-hand-foot malformation and clubfoot disorders. To our knowledge, only nine genes of polydactyly, five genes of split-hand-foot malformation, nine genes for syndactyly, eight genes for brachydactyly and only single gene for clubfoot have been identified to be involved in disease pathophysiology. The current molecular genetic data will help life sciences researchers working on the rare skeletal disorders. Moreover, the aim of present systematic review is to gather the published knowledge on molecular genetics of appendicular skeleton, which would help in genetic counseling and molecular diagnosis.

Intrafamilial variability in six family members with ERF-related craniosynostosis syndrome type 4.

ERF-related craniosynostosis syndrome type 4 (CRS4, OMIM #600775) is a rare autosomal dominant malformation syndrome, caused by pathogenic variants in the ERF gene and characterized by craniosynostosis, developmental delay, and dysmorphic features such as hypertelorism, exophthalmos, depressed nasal bridge, and retrognathia. So far, there are mostly individual reports and only a few descriptions of families with more than two affected patients, allowing statements about the penetrance of a certain variant and its variability only to a limited extent. In this study, we report an in-depth analysis of the clinical course of six family members from three generations with the novel heterozygous nonsense variant c.286A>T (p.Lys96*) in the ERF gene. At the time of examination, all of the six patients showed mild dysmorphic features and brachydactyly, five were overweight/obese and had delayed speech development, and four were short in stature. Hyperactivity, a short concentration span and a history of learning difficulties were found in half of the affected family members. To this day, none of the patients developed increased intracranial hypertension that would require surgical intervention. This work provides further information on the expressive variability of an ERF variant in six members of one family and focuses on the need for close neuropediatric surveillance.

Frameshift Mutation in a Chinese Patient with Brachydactyly Type C Involving the Third Metacarpal: A Case Report.

Brachydactyly is a common feature of congenital hand anomalies characterized by shortening of the phalanges and/or metacarpals. Mutation of growth differentiation factor-5 (GDF5) may result in loss of appearance and function in brachydactyly type C (BDC). Herein, we describe an 11 year-old Chinese BDC patient with significant shortening of the 1st, 2nd, 3rd, and 5th digits. Notably, according to the analysis of metacarpophalangeal pattern profiles, we do not think the 4th digit appears unaffected as usual. In this patient a novel heterozygous frameshift mutation was identified (c.349delG) causing termination of translation after translating six amino acids from codon 117 (p.A117fs*6). This mutation is located in the propeptide region of GDF5, causing GDF5 haploinsufficiency in BDC. Considering our results expanding the genetic spectrum of BDC-causing mutations, further molecular analysis to diagnose and reclassify isolated brachydactyly on the basis of genotype rather than phenotype is warranted.

Aesthetic correction of short nail deformity in congenital brachydactyly Type D by distraction lengthening.

Brachydactyly Type D is a congenital condition of the thumb in which there is a short and broad thumbnail. Although the thumb function is often unaffected, some patients seek surgery for cosmetic improvement. This study aimed to describe our method of distraction lengthening to correct nail deformity in brachydactyly Type D. A total of 163 thumbs in 95 patients underwent this surgery between 2018 and 2021.The mean thumbnail length improved from 9 mm to 15 mm, with a mean percentage increase of 62%. The ratio of nail length to width changed from 0.6 to 1.1, which was equal to normal. The mean increased fingernail length/width ratio was 0.5, with a percentage change of 78%. No obvious surgical scar was observed. The thumb function was not significantly affected. We conclude that aesthetic correction of short nail deformity in brachydactyly Type D can be achieved by distraction lengthening with high satisfaction and without functional impairment.Level of evidence: IV.