Myhre syndrome

Middle Ear Fibrosis Contributes to Hearing Loss in Patients With Myhre Syndrome

Myhre syndrome (MS) is a rare genetic condition that presents with multiple genetic anomalies including cleft lip and palate and Eustachian tube dysfunction. These patients are at a high risk for airway scarring from intubation and mucosal inflammation. Hearing loss (conductive or mixed, of varying severity) is a common comorbidity in these patients, the exact etiology of which is still unclear. We present the cases of 2 unrelated children with MS who suffered progressive mixed hearing loss from fibrosis and obliteration of the middle ear spaces. Both patients had multiple sets of ear tubes that demonstrated early extrusion. The older patient underwent bone conduction implantation at age 11 which resulted in dramatic improvement of speech recognition and interactive skills. The other younger patient demonstrates a similar trajectory but has not yet undergone implantation. Otolaryngologists should take a cautious approach to surgery of the eardrum and middle ear to avoid unnecessary induction of fibrosis in this susceptible patient population. These cases highlight a newly described etiology for hearing loss and suggest a benefit to bone conduction implantation.

Phenotypic characterisation of SMAD4 variant carriers

BACKGROUND

Both hereditary haemorrhagic telangiectasia (HHT) and juvenile polyposis syndrome (JPS) are known to be caused by SMAD4 pathogenic variants, with overlapping symptoms for both disorders in some patients. Additional connective tissue disorders have also been reported. Here, we describe carriers of SMAD4 variants followed in an HHT reference centre to further delineate the phenotype.

METHODS

Observational study based on data collected from the Clinical Investigation for the Rendu-Osler Cohort database.

RESULTS

Thirty-three participants from 15 families, out of 1114 patients with HHT, had an SMAD4 variant (3%).Regarding HHT, 26 out of 33 participants (88%) had a definite clinical diagnosis based on Curaçao criteria. Complication frequencies were as follows: epistaxis (n=27/33, 82%), cutaneous telangiectases (n=19/33, 58%), pulmonary arteriovenous malformations (n=17/32, 53%), hepatic arteriovenous malformations (AVMs) (n=7/18, 39%), digestive angiodysplasia (n=13/22, 59%). No cerebral AVMs were diagnosed.Regarding juvenile polyposis, 25 out of 31 participants (81%) met the criteria defined by Jass et al for juvenile polyposis syndrome. Seven patients (21%) had a prophylactic gastrectomy due to an extensive gastric polyposis incompatible with endoscopic follow-up, and four patients (13%) developed a digestive cancer.Regarding connective tissue disorders, 20 (61%) had at least one symptom, and 4 (15%) participants who underwent echocardiography had an aortic dilation.

CONCLUSION

We describe a large cohort of SMAD4 variant carriers in the context of HHT. Digestive complications are frequent, early and diffuse, justifying endoscopy every 2 years. The HHT phenotype, associating pulmonary and hepatic AVMs, warrants systematic screening. Connective tissue disorders broaden the phenotype associated with SMAD4 gene variants and justify systematic cardiac ultrasound and skeletal complications screening.

miR-431 secreted by human vestibular schwannomas increases the mammalian inner ear's vulnerability to noise trauma

Introduction

Vestibular schwannoma (VS) is an intracranial tumor that arises on the vestibular branch of cranial nerve VIII and typically presents with sensorineural hearing loss (SNHL). The mechanisms of this SNHL are postulated to involve alterations in the inner ear's microenvironment mediated by the genetic cargo of VS-secreted extracellular vesicles (EVs). We aimed to identify the EV cargo associated with poor hearing and determine whether its delivery caused hearing loss and cochlear damage in a mouse model in vivo.

Methods

VS tissue was collected from routinely resected tumors of patients with good (VS-GH) or poor (VS-PH) pre-surgical hearing measured via pure-tone average and word recognition scores. Next-generation sequencing was performed on RNA isolated from cultured primary human VS cells and EVs from VS-conditioned media, stratified by patients' hearing ability. microRNA expression levels were compared between VS-PH and VS-GH samples to identify differentially expressed candidates for packaging into a synthetic adeno-associated viral vector (Anc80L65). Viral vectors containing candidate microRNA were infused to the semicircular canals of mice to evaluate the effects on hearing, including after noise exposure.

Results

Differentially expressed microRNAs included hsa-miR-431-5p (enriched in VS-PH) and hsa-miR-192-5p (enriched in VS-GH). Newborn mice receiving intracochlear injection of viral vectors over-expressing hsa-miR-431-GFP, hsa-miR-192-GFP, or GFP only (control) had similar hearing 6 weeks post-injection. However, after acoustic trauma, the miR-431 group displayed significantly worse hearing, and greater loss of synaptic ribbons per inner hair cell in the acoustically traumatized cochlear region than the control group.

Conclusion

Our results suggest that miR-431 contributes to VS-associated hearing loss following cochlear stress. Further investigation is needed to determine whether miR-431 is a potential therapeutic target for SNHL.

A novel germline SMAD4 variant detected in a Japanese family with juvenile polyposis syndrome and hereditary hemorrhagic telangiectasia

Juvenile polyposis syndrome (JPS) is an autosomal dominant, inherited disorder caused by pathogenic germline variants of mainly SMAD4 or BMPR1A genes. Some patients with JPS, especially with SMAD4 variants, also develop hereditary, hemorrhagic telangiectasia (HHT). HHT is also an autosomal dominant inherited disorder. Herein, we identified a novel germline pathogenic variant of the SMAD4 in a Japanese family with JPS and HHT. A six-base pair deletion in the SMAD4 gene (NM_005359.6:c.1495_1500delTGCATA) was identified in the patients. Two amino acids are deleted from SMAD4 protein (p.Cys499_Ile500del), which are located in MSH2 domain essential for the binding with SMAD3. This is a novel variant that has not been registered in any database surveyed. Amino acid structural analysis predicted significant changes in the secondary and three-dimensional structures in the vicinity of the two amino acids' deletion. The variant is classified as 'Likely Pathogenic' according to the American College of Medical Genetics and Genomics guidelines.

A newborn male with Myhre syndrome, hearing loss, and complete syndactyly of fingers 3-4

BACKGROUND

Myhre syndrome is a rare multisystem genetic disorder that is caused by de novo heterozygous gain-of-function variants in SMAD4. Patients with Myhre syndrome exhibit several phenotypes at different ages such as small size, autism, developmental delay, left-sided heart defects, and hearing loss and often have a characteristic facial appearance. The early clinical diagnosis of Myhre syndrome remains a major challenge, particularly in the first year of life.

METHODS

A Chinese male infant with syndactyly of fingers, hypertelorism, short palpebral fissures, and short philtrum was enrolled into the ENT department of the Chinese PLA General Hospital. Whole exome sequencing analysis was used to detect the disease-causing variant. A literature review of Myhre syndrome was also performed.

RESULTS

A recurrent de novo missense variant c.1498A > G p.I500V(p. Ile500Val) in SMAD4 was detected confirming the clinical diagnosis of Myhre syndrome at the age of 38 days. The infant appears to be the youngest reported case of Myhre syndrome. At 23-month follow-up, the affected infant has dysmorphic facial features, growth retardation, and previously undescribed complete syndactyly. Review the literatures noted several common features in Myhre syndrome patients including hearing loss (72.7%), characteristic facial features (26.0%-54.5%), finger and toe abnormalities (3.9%-48.1%), short stature (45.5%), and respiratory (30.0%) and cardiovascular problems (65.0%).

CONCLUSIONS

Clinicians should have a low threshold to perform genetic testing on patients with features suggesting Myhre syndrome even in the first year of life. Although some individuals with Myhre syndrome have normal hearing, early onset or progressive hearing loss usually occur in one or both ears in most patients, with remarkable phenotypic heterogeneity. Syndactyly may be minor such as typical 2-3 toe involvement, or more complicated as was observed in our patient.

Natural history of Myhre syndrome

Background

Myhre syndrome (MS) is a rare genetic disease characterized by skeletal disorders, facial features and joint limitation, caused by a gain of function mutation in SMAD4 gene. The natural history of MS remains incompletely understood.

Methods

We recruited in a longitudinal retrospective study patients with molecular confirmed MS from the French reference center for rare skeletal dysplasia. We described natural history by chaining data from medical reports, clinical data warehouse, medical imaging and photographies.

Results

We included 12 patients. The median age was 22 years old (y/o). Intrauterine and postnatal growth retardation were consistently reported. In preschool age, neurodevelopment disorders were reported in 80% of children. Specifics facial and skeletal features, thickened skin and joint limitation occured mainly in school age children. The adolescence was marked by the occurrence of pulmonary arterial hypertension (PAH) and vascular stenosis. We reported for the first time recurrent strokes from the age of 26 y/o, caused by a moyamoya syndrome in one patient. Two patients died at late adolescence and in their 20 s respectively from PAH crises and mesenteric ischemia.

Conclusion

Myhre syndrome is a progressive disease with severe multisystemic impairement and life-threathning complication requiring multidisciplinary monitoring.

Pathogenic Copy Number and Sequence Variants in Children Born SGA With Short Stature Without Imprinting Disorders

CONTEXT

Children born small-for-gestational-age with short stature (SGA-SS) is associated with (epi)genetic defects, including imprinting disorders (IDs), pathogenic copy number variants (PCNVs), and pathogenic variants of genes involved in growth. However, comprehensive studies evaluating these 3 factors are very limited.

OBJECTIVE

To clarify the contribution of PCNVs and candidate pathogenic variants to SGA-SS.

DESIGN

Comprehensive molecular analyses consisting of methylation analysis, copy number analysis, and multigene sequencing.

METHODS

We enrolled 140 patients referred to us for genetic testing for SGA-SS. Among them, we excluded 42 patients meeting Netchine-Harbison clinical scoring system criteria for Silver-Russell syndrome and 4 patients with abnormal methylation levels of the IDs-related differentially methylated regions. Consequently, we conducted copy number analysis and multigene sequencing for 86 SGA-SS patients with sufficient sample volume. We also evaluated clinical phenotypes of patients with PCNVs or candidate pathogenic variants.

RESULTS

We identified 8 (9.3%) and 11 (12.8%) patients with PCNVs and candidate pathogenic variants, respectively. According to the American College of Medical Genetics standards and guidelines, 5 variants were classified as pathogenic and the remaining 6 variants were classified as variants of unknown significance. Genetic diagnosis was made in 12 patients. All patients with PCNVs or candidate pathogenic variants did not correspond perfectly to characteristic clinical features of each specific genetic cause.

CONCLUSION

We clarified the contribution of PCNVs and pathogenic variants to SGA-SS without IDs. Comprehensive molecular analyses, including copy number analysis and multigene sequencing, should be considered for patients with unknown SGA-SS etiology.

First documented case of Myhre syndrome in Romania: A case report

Myhre syndrome is a rare genetic autosomal dominant connective tissue disorder, characterized by developmental delay, characteristic facial features, various bone and joint abnormalities, distinctive cardiovascular, ophthalmological and ear, nose and throat (ENT) manifestations, in association with mild to moderate intellectual disability and autism or autism spectrum disorder-like behaviour. The diagnosis of Myhre syndrome is established corroborating the clinical findings with SMAD4 heterozygous mutation identified in the majority of the patients. SMAD4 gene mutations result in abnormal TGF-β signalling in several cell types, which affects the development of several body systems and leads to the specific phenotype of Myhre syndrome. We herein report the case of an 18-year-old female patient who was diagnosed at the age of 17 years with Myhre syndrome, the first documented case of this syndrome in Romania. Sequence analysis of protein-coding genes using whole-exome analysis identified a ‘de novo’, heterozygous missense variant of SMAD4, c.1498A>G, p. (Ile500Val), which is pathogenic for Myhre syndrome. Although this condition is rare, a series of particularities were identified in the present case, consisting of severe allergic reactions, recurrent ENT tumour development and delayed dental eruption, which have not been described in Myhre syndrome to date, to the best of the authors' knowledge.

What Every Internist-Endocrinologist Should Know about Rare Genetic Syndromes in Order to Prevent Needless Diagnostics, Missed Diagnoses and Medical Complications: Five Years of 'Internal Medicine for Rare Genetic Syndromes'

Patients with complex rare genetic syndromes (CRGS) have combined medical problems affecting multiple organ systems. Pediatric multidisciplinary (MD) care has improved life expectancy, however, transfer to internal medicine is hindered by the lack of adequate MD care for adults. We have launched an MD outpatient clinic providing syndrome-specific care for adults with CRGS, which, to our knowledge, is the first one worldwide in the field of internal medicine. Between 2015 and 2020, we have treated 720 adults with over 60 syndromes. Eighty-nine percent of the syndromes were associated with endocrine problems. We describe case series of missed diagnoses and patients who had undergone extensive diagnostic testing for symptoms that could actually be explained by their syndrome. Based on our experiences and review of the literature, we provide an algorithm for the clinical approach of health problems in CRGS adults. We conclude that missed diagnoses and needless invasive tests seem common in CRGS adults. Due to the increased life expectancy, an increasing number of patients with CRGS will transfer to adult endocrinology. Internist-endocrinologists (in training) should be aware of their special needs and medical pitfalls of CRGS will help prevent the burden of unnecessary diagnostics and under- and overtreatment.

Myhre syndrome: the first case in Korea

Myhre syndrome (MS) is a rare autosomal-dominant disorder characterized by short stature, intellectual disability, skeletal anomalies, restricted joint mobility, distinctive facial dysmorphism, and deafness. Early diagnosis of MS is difficult because its features progress and become noticeable at school age. Recently, the SMAD4 gene was identified as the major gene responsible for MS. Herein, we report the first Korean case of MS after identification of a SMAD4 mutation by clinical exome sequencing. The patient was born small for gestational age, and she had the typical clinical features of MS, including short stature, characteristic facial appearance, developmental delay, and selective mutism. She was diagnosed with central precocious puberty. Because of the patient's precocious puberty and short stature, we administered combined recombinant human growth hormone and gonadotropin-releasing hormone agonist treatments, which resulted in improved height. While there have been 79 cases of MS reported worldwide, to our knowledge, this is the first case of genetically-confirmed MS in Korea.

Benefit of cochlear implantation in a patient with Myhre syndrome

Myhre syndrome is a rare disorder characterised by short stature, skeletal anomalies, facial dysmorphism and hearing loss (HL), resulting from heterozygous mutations of the SMAD4 gene. We describe the benefits of cochlear implant (CI) in a patient with sensorineural HL carrying a mutation (NM_005359.6: c.1498A>G; p.lle500Val) within the SMAD4 gene, detected by whole-exome sequencing. The CI was inserted through the round window despite otospongiotic abnormalities. Pure-tone audiometry improved up to 20 dBHL. Speech perception in noise (Simplified Noise Reduction - SNR +10) increased from 0% pre implantation with hearing aids to 50% post implantation. The postoperative setting of the electrical stimulation limits yielded an asymmetric map, with lower levels for central electrodes and higher levels for lateral ones. Action potential could not be evoked via medial electrodes, suggesting a cochlear nerve dysfunction. Outcomes related to quality of life and cognitive impairment improved. CI was shown to be an effective auditory rehabilitation strategy.

Signaling Pathways in Bone Development and Their Related Skeletal Dysplasia

Bone development is a tightly regulated process. Several integrated signaling pathways including HH, PTHrP, WNT, NOTCH, TGF-β, BMP, FGF and the transcription factors SOX9, RUNX2 and OSX are essential for proper skeletal development. Misregulation of these signaling pathways can cause a large spectrum of congenital conditions categorized as skeletal dysplasia. Since the signaling pathways involved in skeletal dysplasia interact at multiple levels and have a different role depending on the time of action (early or late in chondrogenesis and osteoblastogenesis), it is still difficult to precisely explain the physiopathological mechanisms of skeletal disorders. However, in recent years, significant progress has been made in elucidating the mechanisms of these signaling pathways and genotype–phenotype correlations have helped to elucidate their role in skeletogenesis. Here, we review the principal signaling pathways involved in bone development and their associated skeletal dysplasia.

Case Report: Improved Height in a Patient With Myhre Syndrome Using a Combination of Growth Hormone and Letrozole

Myhre syndrome is a rare disorder caused by a heterozygous mutation in the SMAD4 gene. Affected patients may exhibit dysmorphic facial features, intrauterine growth retardation, short stature, obesity, muscle hypertrophy, thickened skin, limited joint movement, hearing impairment, and varying degrees of psychomotor developmental disorder. Serious complications of the cardiovascular and respiratory system may be seen later in life. We report the case of a Chinese boy with Myhre syndrome presenting with a novel symptom of giant testicles where treatment with growth hormone combined with letrozole successfully improved his short stature. This case shows that letrozole combined with growth hormone can improve height in children with Myhre syndrome without adverse effects.

A pilot clinical trial with losartan in Myhre syndrome

Introduction

Myhre syndrome (MS) is an ultra‐rare disorder due to pathogenic variants in the SMAD4 gene that encodes a protein regulating the TGF‐β pathway and extra‐cellular matrix (ECM) homeostasis. Main clinical features of MS include thickening of skin and joint stiffness. Previous studies showed that losartan improved ECM deposition in MS fibroblasts.

Materials and methods

Four molecularly confirmed MS subjects (mean age 23.8 ± 17 years) were evaluated for: (a) skin thickness by Rodnan score, (b) joint range of motion (ROM) by goniometry, and (c) speckle‐tracking echocardiogram. Following baseline evaluations, three MS individuals received losartan for 12 months and pre‐defined endpoints were monitored after 6 and 12 months of treatment.

Results

At baseline, Rodnan scores were increased, joint ROM was reduced, and speckle‐tracking echocardiogram revealed reduced myocardial strain. In three MS subjects, improvements in skin thickness, joint ROM and to a lesser extent of myocardial strain, were observed after 6 and 12 months of losartan treatment.

Conclusions

Although further long‐term controlled clinical trials with a larger number of affected individuals are needed, the present study suggests that losartan might improve skin, joint and heart abnormalities of MS.

Myhre Syndrome Associated With Dunbar Syndrome and Urinary Tract Abnormalities: A Case Report

Myhre syndrome is a rare condition caused by a mutation in the SMAD4 gene, which leads to a defective TGF-β/BMP signaling, resulting in the proliferation of abnormal fibrous tissues. Clinically, patients with Myhre syndrome manifest with defects of connective tissue (skin, muscles, joints), and cardiovascular and neurological impairment. In our report, we present a case of a 16-year-old female with skeletal abnormalities, reduced articular mobility, skin, and muscular hypertrophy and cardiovascular defects characteristic of Myhre syndrome. Long-term pulmonary hypertension and arterial hypertension were persistent in spite of antihypertensive treatment. Our patient was also diagnosed with chronic kidney disease and Dunbar syndrome, which is an external compression of the coeliac trunk or coeliac artery by the surrounding tissues. Until now, only a few cases of renal complications in Myhre syndrome have been published. We describe for the first time a female patient with genetically confirmed Myhre syndrome caused by the p.Ile500Val SMAD4 mutation presenting with an unusual occurrence of congenital vesicoureteral reflux, proteinuria with a decreased renal function, and a condition recognized as Dunbar syndrome.

Novel Ocular and Inner Ear Anomalies in a Patient with Myhre Syndrome

Myhre syndrome is a rare autosomal dominant multisystemic disorder. Typical features of this disorder include distinctive facial appearance, deafness, intellectual disability, cardiovascular abnormalities, short stature, brachydactyly, and skeletal anomalies. Gain-of-function mutations in the SMAD4 gene are responsible for this syndrome. Herein, we present a 9.6-year-old Turkish girl with molecularly confirmed Myhre syndrome who had novel findings including bilateral Axenfield Rieger anomaly with secondary glaucoma and bilateral enlarged vestibular aqueducts.

Gain-of-function pathogenic variants in SMAD4 are associated with neoplasia in Myhre syndrome

Myhre syndrome is an increasingly diagnosed rare syndrome that is caused by one of two specific heterozygous gain-of-function pathogenic variants in SMAD4. The phenotype includes short stature, characteristic facial appearance, hearing loss, laryngotracheal stenosis, arthritis, skeletal abnormalities, learning and social challenges, distinctive cardiovascular defects, and a striking fibroproliferative response in the ear canals, airways, and serosal cavities (peritoneum, pleura, pericardium). Confirmation of the clinical diagnosis is usually prompted by the characteristic appearance with developmental delay and autistic-like behavior using targeted gene sequencing or by whole exome sequencing. We describe six patients (two not previously reported) with molecularly confirmed Myhre syndrome and neoplasia. Loss-of-function pathogenic variants in SMAD4 cause juvenile polyposis syndrome and we hypothesize that the gain-of-function pathogenic variants observed in Myhre syndrome may contribute to neoplasia in the patients reported herein. The frequency of neoplasia (9.8%, 6/61) in this series (two new, four reported patients) and endometrial cancer (8.8%, 3/34, mean age 40 years) in patients with Myhre syndrome, raises the possibility of cancer susceptibility in these patients. We alert clinicians to the possibility of detecting this syndrome when cancer screening panels are used. We propose that patients with Myhre syndrome are more susceptible to neoplasia, encourage increased awareness, and suggest enhanced clinical monitoring.

The first two Chinese Myhre syndrome patients with the recurrent SMAD4 pathogenic variants: Functional consequences and clinical diversity

Myhre syndrome is a rare autosomal dominant multi-organ disorder characterized by growth retardation, skeletal anomalies, muscular hypertrophy, joint stiffness, facial dysmorphism, deafness, cardiovascular disease, and abnormal sexual development. Here we described the first two Chinese Myhre syndrome patients diagnosed by whole-exome sequencing. They both had de novo c.1498A > G (p.Ile500Val) variant in SMAD4 and presented with key characteristics of Myhre syndrome but also revealed uncommon features (polydactyly in the girl and precocious puberty in the boy). We performed functional analysis on four previously reported SMAD4 pathogenic variants in Myhre syndrome patients using dual-luciferase assay. Our results revealed that the pathogenic variants resulted in a variable degree of increased transcription activity of target genes that contain the minimal SMAD binding elements in their promoter regions. The boy responded to the recombinant human growth hormone treatment with improved height but also led to hyperinsulinemia and advanced bone age. Because of his precocious puberty, we subsequently combined the recombinant human growth hormone and gonadotrophin-releasing hormone agonist treatments, which resulted in overall improved height. We reviewed the sexual features of reported Myhre syndrome cases and discussed the possible mechanism of SMAD4 variants in Myhre syndrome that lead to the abnormal hypothalamic-pituitary-gonadal axis.

Philtrum length and intercommissural distance measurements at mixed dentition period

Anthropometric measurements of the lip and mouth are of great importance in clinical dysmorphology as well as reconstructive plastic surgery. In this study, the philtrum length (PhL) and intercommissural distance (ICmD) nomograms for Egyptian children in the mixed dentition period were established. A group of 1,338 Egyptian students in primary schools (735 boys and 603 girls) were included in the study. The students were at mixed dentition period and their ages ranged from 7 to 12 years. Anthropometric norms of PhL and ICmD were developed with significant sex difference in certain groups. A ratio between PhL and ICmD was developed. These data will help facilitate both objective and subjective evaluation of the lip and mouth for proper diagnosis of orofacial anomalies and variations as well as for ideal treatment plans.

Smad4 regulates growth plate matrix production and chondrocyte polarity

Smad4 is an intracellular effector of the TGFβ family that has been implicated in Myhre syndrome, a skeletal dysplasia characterized by short stature, brachydactyly and stiff joints. The TGFβ pathway also plays a critical role in the development, organization and proliferation of the growth plate, although the exact mechanisms remain unclear. Skeletal phenotypes in Myhre syndrome overlap with processes regulated by the TGFβ pathway, including organization and proliferation of the growth plate and polarity of the chondrocyte. We used in vitro and in vivo models of Smad4 deficiency in chondrocytes to test the hypothesis that deregulated TGFβ signaling leads to aberrant extracellular matrix production and loss of chondrocyte polarity. Specifically, we evaluated growth plate chondrocyte polarity in tibiae of Col2-Cre^+/−;Smad4^fl/fl mice and in chondrocyte pellet cultures. In vitro and in vivo, Smad4 deficiency decreased aggrecan expression and increased MMP13 expression. Smad4 deficiency disrupted the balance of cartilage matrix synthesis and degradation, even though the sequential expression of growth plate chondrocyte markers was intact. Chondrocytes in Smad4-deficient growth plates also showed evidence of polarity defects, with impaired proliferation and ability to undergo the characteristic changes in shape, size and orientation as they differentiated from resting to hypertrophic chondrocytes. Therefore, we show that Smad4 controls chondrocyte proliferation, orientation, and hypertrophy and is important in regulating the extracellular matrix composition of the growth plate.

Summary: Smad4 is a key regulator of extracellular matrix production and chondrocyte proliferation, shape and orientation in the growth plate. Smad4 dysregulation results in skeletal dysplasias, such as Myhre syndrome.

Neuroimaging Findings in Pediatric Genetic Skeletal Disorders: A Review

Genetic skeletal disorders (GSDs) are a heterogeneous group characterized by an intrinsic abnormality in growth and (re-)modeling of cartilage and bone. A large subgroup of GSDs has additional involvement of other structures/organs beside the skeleton, such as the central nervous system (CNS). CNS abnormalities have an important role in long-term prognosis of children with GSDs and should consequently not be missed. Sensitive and specific identification of CNS lesions while evaluating a child with a GSD requires a detailed knowledge of the possible associated CNS abnormalities. Here, we provide a pattern-recognition approach for neuroimaging findings in GSDs guided by the obvious skeletal manifestations of GSD. In particular, we summarize which CNS findings should be ruled out with each GSD. The diseases (n = 180) are classified based on the skeletal involvement (1. abnormal metaphysis or epiphysis, 2. abnormal size/number of bones, 3. abnormal shape of bones and joints, and 4. abnormal dynamic or structural changes). For each disease, skeletal involvement was defined in accordance with Online Mendelian Inheritance in Man. Morphological CNS involvement has been described based on extensive literature search. Selected examples will be shown based on prevalence of the diseases and significance of the CNS involvement. CNS involvement is common in GSDs. A wide spectrum of morphological abnormalities is associated with GSDs. Early diagnosis of CNS involvement is important in the management of children with GSDs. This pattern-recognition approach aims to assist and guide physicians in the diagnostic work-up of CNS involvement in children with GSDs and their management.

Natural history and life-threatening complications in Myhre syndrome and review of the literature

Myhre syndrome (OMIM 139210) is a rare developmental disorder inherited as an autosomal dominant trait and caused by a narrow spectrum of missense mutations in the SMAD4 gene. The condition features characteristic face, short stature, skeletal anomalies, muscle pseudohypertrophy, restricted joint mobility, stiff and thick skin, and variable intellectual disability. While most of the clinical features manifest during childhood, the diagnosis may be challenging during the first years of life. We report on the evolution of the clinical features of Myhre syndrome during childhood in a subject with molecularly confirmed diagnosis. The clinical records of 48 affected patients were retrospectively analysed to identify any early clinical signs characterizing this disorder and to better delineate its natural history. We also note that pericarditis and laryngotracheal involvement represent important life-threatening complications of Myhre syndrome that justify the recommendation for cardiological and ENT follow-up for these patients.

CONCLUSION

Short length/stature, short palpebral fissures, and brachydactyly with hyperconvex nails represent signs/features that might lead to the correct diagnosis in the first years of life and direct to the proper molecular analysis. We underline the clinical relevance of pericarditis and laryngotracheal stenosis as life-threatening complications of this disorder and the need for careful monitoring, in relation to their severity.

WHAT IS KNOWN

• The clinical and radiological signs of the disease in children older than 7-8 years. • Pericarditis, sometimes occurring with constrictive pericardium requiring pericardiectomy, has been reported as a recurrent feature but has not been adequately stressed in previous literature. What is New: • Short length/stature, short palpebral fissures, brachydactyly with hyperconvex nails represent clinical signs that might lead to diagnosis in the first years of life. • Review of the literature showed that pericarditis and laryngotracheal complications represent major recurrent issues in patients with Myhre syndrome.

Mutations in LTBP3 cause acromicric dysplasia and geleophysic dysplasia

BACKGROUND

Acromelic dysplasias are a group of disorders characterised by short stature, brachydactyly, limited joint extension and thickened skin and comprises acromicric dysplasia (AD), geleophysic dysplasia (GD), Myhre syndrome and Weill-Marchesani syndrome. Mutations in several genes have been identified for these disorders (including latent transforming growth factor β (TGF-β)-binding protein-2 (LTBP2), ADAMTS10, ADAMSTS17 and fibrillin-1 (FBN1) for Weill-Marchesani syndrome, ADAMTSL2 for recessive GD and FBN1 for AD and dominant GD), encoding proteins involved in the microfibrillar network. However, not all cases have mutations in these genes.

METHODS

Individuals negative for mutations in known acromelic dysplasia genes underwent whole exome sequencing.

RESULTS

A heterozygous missense mutation (exon 14: c.2087C>G: p.Ser696Cys) in latent transforming growth factor β (TGF-β)-binding protein-3 (LTBP3) was identified in a dominant AD family. Two distinct de novo heterozygous LTPB3 mutations were also identified in two unrelated GD individuals who had died in early childhood from respiratory failure-a donor splice site mutation (exon 12 c.1846+5G>A) and a stop-loss mutation (exon 28: c.3912A>T: p.1304*Cysext*12).

CONCLUSIONS

The constellation of features in these AD and GD cases, including postnatal growth retardation of long bones and lung involvement, is reminiscent of the null ltbp3 mice phenotype. We conclude that LTBP3 is a novel component of the microfibrillar network involved in the acromelic dysplasia spectrum.

BMP signalling in skeletal development, disease and repair

Since the identification in 1988 of bone morphogenetic protein 2 (BMP2) as a potent inducer of bone and cartilage formation, BMP superfamily signalling has become one of the most heavily investigated topics in vertebrate skeletal biology. Whereas a large part of this research has focused on the roles of BMP2, BMP4 and BMP7 in the formation and repair of endochondral bone, a large number of BMP superfamily molecules have now been implicated in almost all aspects of bone, cartilage and joint biology. As modulating BMP signalling is currently a major therapeutic target, our rapidly expanding knowledge of how BMP superfamily signalling affects most tissue types of the skeletal system creates enormous potential to translate basic research findings into successful clinical therapies that improve bone mass or quality, ameliorate diseases of skeletal overgrowth, and repair damage to bone and joints. This Review examines the genetic evidence implicating BMP superfamily signalling in vertebrate bone and joint development, discusses a selection of human skeletal disorders associated with altered BMP signalling and summarizes the status of modulating the BMP pathway as a therapeutic target for skeletal trauma and disease.

Myhre syndrome: Clinical features and restrictive cardiopulmonary complications

Myhre syndrome, a connective tissue disorder characterized by deafness, restricted joint movement, compact body habitus, and distinctive craniofacial and skeletal features, is caused by heterozygous mutations in SMAD4. Cardiac manifestations reported to date have included patent ductus arteriosus, septal defects, aortic coarctation and pericarditis. We present five previously unreported patients with Myhre syndrome. Despite varied clinical phenotypes all had significant cardiac and/or pulmonary pathology and abnormal wound healing. Included herein is the first report of cardiac transplantation in patients with Myhre syndrome. A progressive and markedly abnormal fibroproliferative response to surgical intervention is a newly delineated complication that occurred in all patients and contributes to our understanding of the natural history of this disorder. We recommend routine cardiopulmonary surveillance for patients with Myhre syndrome. Surgical intervention should be approached with extreme caution and with as little invasion as possible as the propensity to develop fibrosis/scar tissue is dramatic and can cause significant morbidity and mortality.

Myhre-LAPs syndrome and intubation related airway stenosis: keys to diagnosis and critical therapeutic interventions

OBJECTIVES

Myhre-LAPS syndrome is a recently recognized disease caused by a mutation in the SMAD4 gene. This results in a range of pathology including laryngotracheal stenosis, arthropathy, prognathism and short stature, or LAPS syndrome. We aim to delineate the role of intubation in development of airway stenosis in these patients as well as provide insight into diagnosis and management of this syndrome. Herein we present four patients with Myhre-LAPS syndrome complicated by airway stenosis and perform a systematic review of all cases of Myhre-LAPS syndrome with reported airway pathology.

STUDY DESIGN

Retrospective review

METHODS

All patients diagnosed with Myhre-LAPS syndrome and airway stenosis at a single institution from 1981 to 2014 were reviewed.

RESULTS

Four patients (4F, median age 42) were identified that met inclusion criteria. Initial presenting signs included progressive shortness of breath, dyspnea on exertion and respiratory distress. All four (100%) patients had multi-level airway stenosis most commonly in the subglottic and glottic regions and all patients had undergone at least one endotracheal intubation prior to presentation. One patient with a history of nasal tracheal intubation presented with nasal obstruction and was found to have choanal as well as subglottic stenosis. Two of the four (50%) patients are tracheostomy tube dependent, 1/4 (25%) died of a fatal cardiac arrhythmia and 1/4 (25%) has had 6 endoscopic treatments for subglottic stenosis in 4 years with rapid symptom recurrence.

CONCLUSIONS

Myhre-LAPS syndrome is characterized by progressive systemic fibrosis and patients are diagnosed by characteristic findings of prognathism, short stature, abnormal facies, and thick skin among other abnormalities. Airway management is complicated by recurrent, refractory subglottic stenosis often preceded by elective intubation as well as maxillary hypoplasia, trismus, and limited neck extension. Endotracheal intubation and surgical intervention should be approached with caution in these patients and multidisciplinary care teams are necessary to address all manifestations of this syndrome.

Chondrodysplasias and TGFβ signaling

Human chondrodysplasias are a group of conditions that affect the cartilage. This review is focused on the involvement of transforming growth factor-β signaling in a group of chondrodysplasias, entitled acromelic dysplasia, characterized by short stature, short hands and restricted joint mobility.