Gain-of-function variants in SMAD4 compromise respiratory epithelial function.

BACKGROUND: Myhre syndrome is an exceedingly rare yet increasingly diagnosed genetic disorder arising from germline variants in the SMAD4 gene. Its core manifestation is the progression of stiffness and fibrosis across multiple organs. Individuals with Myhre syndrome exhibit a propensity for upper respiratory tract remodeling and infections. The molecular and cellular mechanisms underlying this phenotype remain unclear. OBJECTIVE: We sought to investigate how SMAD4 pathogenic variants associated with Myhre syndrome affect SMAD4 protein levels, activation, and physiological functions in patient-derived nasal epithelial cells. METHODS: Clinical observations were conducted on a cohort of 47 patients recruited at Massachusetts General Hospital from 2016 to 2023. Nasal epithelial basal cells were isolated and cultured from inferior turbinate brushings of healthy subjects (n = 8) and patients with Myhre syndrome (n = 3; SMAD4-Ile500Val, Arg496Cys, and Ile500Thr). Transcriptomic analysis and functional assays were performed to assess SMAD4 levels, transcriptional activity, and epithelial cell host defense functions, including cell proliferation, mucociliary differentiation, and bacterial elimination. RESULTS: Clinical observations revealed a prevalent history of otitis media and sinusitis among most individuals with Myhre syndrome. Analyses of nasal epithelial cells indicated that SMAD4 mutations do not alter SMAD4 protein stability or upstream regulatory SMAD phosphorylation but enhance signaling transcriptional activity, supporting a gain-of-function mechanism, likely attributable to increased protein-protein interaction of the SMAD complex. Consequently, Myhre syndrome nasal basal cells exhibit reduced potential in cell proliferation and mucociliary differentiation. Furthermore, Myhre syndrome nasal epithelia are impaired in bacterial killing. CONCLUSIONS: Compromised innate immunity originating from epithelial cells in Myhre syndrome may contribute to increased susceptibility to upper respiratory tract infections.

Prenatal Diagnosis of Myhre Syndrome in Two Cases: Further Delineation of the Cardiac and External Phenotype.

Myhre syndrome is a rare genetic disease caused by recurrent gain-of-function variants in SMAD4 (Ile500Thr, Ile500Val, Arg496Cys, and Ile500Met) characterized by postnatal short stature with pseudo-muscular build, joint stiffness, variable intellectual disability, hearing loss, and a distinctive pattern of dysmorphic facial features. The course can be severe in some cases, with life-threatening cardiac and pulmonary complications caused by connective tissue involvement. These progressive features over time make early clinical diagnosis difficult but possible by astute clinicians who evaluate young children with autism or short stature and unusual appearance. Only two cases of Myhre syndrome diagnosed during the prenatal period have been reported. Here, we present a detailed description of two unrelated fetuses with Myhre syndrome, each molecularly confirmed by genome or exome sequencing, who underwent fetal examination after termination of pregnancy. One had severe intrauterine growth retardation associated with crossed fused renal ectopia, and the other one had pulmonary atresia with ventricular septal defect (a form of tetralogy of Fallot). Both had mild dysmorphic features with a wide nasofrontal angle. Our results and a systematic prenatal literature review add insight into the early natural history of Myhre syndrome and highlight the contribution of prenatal next-generation sequencing in prenatal diagnosis and the importance of fetal autopsy in Myhre syndrome.

Myhre syndrome is caused by dominant-negative dysregulation of SMAD4 and other co-factors.

Myhre syndrome is a connective tissue disorder characterized by congenital cardiovascular, craniofacial, respiratory, skeletal, and cutaneous anomalies as well as intellectual disability and progressive fibrosis. It is caused by germline variants in the transcriptional co-regulator SMAD4 that localize at two positions within the SMAD4 protein, I500 and R496, with I500 V/T/M variants more commonly identified in individuals with Myhre syndrome. Here we assess the functional impact of SMAD4-I500V variant, identified in two previously unpublished individuals with Myhre syndrome, and provide novel insights into the molecular mechanism of SMAD4-I500V dysfunction. We show that SMAD4-I500V can dimerize, but its transcriptional activity is severely compromised. Our data show that SMAD4-I500V acts dominant-negatively on SMAD4 and on receptor-regulated SMADs, affecting transcription of target genes. Furthermore, SMAD4-I500V impacts the transcription and function of crucial developmental transcription regulator, NKX2-5. Overall, our data reveal a dominant-negative model of disease for SMAD4-I500V where the function of SMAD4 encoded on the remaining allele, and of co-factors, are perturbed by the continued heterodimerization of the variant, leading to dysregulation of TGF and BMP signaling. Our findings not only provide novel insights into the mechanism of Myhre syndrome pathogenesis but also extend the current knowledge of how pathogenic variants in SMAD proteins cause disease.

Myhre syndrome: expanding its paediatric phenotypic spectrum.

Myhre syndrome is a rare disease secondary to pathogenic variants in SMAD4 gene. It is a multisystem disease characterised by short stature, deafness, joint stiffness, craniofacial dysmorphism, and potential cardiac manifestations. Herein, we report two new paediatric cases of Myhre syndrome who, additionally, presented with mid-aortic syndrome. This confirms and extends the scarce reports describing the association between these two entities.

An additional patient with SMAD4-Juvenile Polyposis-Hereditary hemorrhagic telangiectasia and connective tissue abnormalities: SMAD4 loss-of-function and gain-of-function pathogenic variants result in contrasting phenotypes.

Loss-of-function pathogenic variants in somatic and germline cells in SMAD4 may cause cancer and juvenile polyposis-Hereditary Hemorrhagic Telangiectasia (SMAD4-JP-HHT), respectively. In a similar manner, gain-of-function somatic and germline pathogenic variants in SMAD4 can cause various forms of cancer as well as Myhre syndrome. The different SMAD4 molecular mechanisms result in contrasting clinical phenotypes demonstrated by SMAD4-JP-HHT and Myhre syndrome. We report an additional patient with SMAD4-JP-HHT and aortopathy, and expand the phenotype to include severe valvulopathy, cutaneous, ophthalmologic, and musculoskeletal features consistent with an inherited disorder of connective tissue. We compared this 70-year-old man with SMAD4-JP-HHT to 18 additional literature cases, and also compared patients with SMAD4-JP-HHT to those with Myhre syndrome. In contrast to aorta dilation, hypermobility, and loose skin in SMAD4-JP-HHT, Myhre syndrome has aorta hypoplasia, stiff joints, and firm skin representing an intriguing phenotypic contrast, which can be attributed to different molecular mechanisms involving SMAD4. We remind clinicians about the possibility of significant cardiac valvulopathy and aortopathy, as well as connective tissue disease in SMAD4-JP-HHT. Additional patients and longer follow-up will help determine if more intensive surveillance improves care amongst these patients.

Expanded cardiovascular phenotype of Myhre syndrome includes tetralogy of Fallot suggesting a role for SMAD4 in human neural crest defects.

Tetralogy of Fallot (ToF) can be associated with a wide range of extracardiac anomalies, with an underlying etiology identified in approximately 10% of cases. Individuals affected with Myhre syndrome due to recurrent SMAD4 mutations frequently have cardiovascular anomalies, including congenital heart defects. In addition to two patients in the literature with ToF, we describe five additional individuals with Myhre syndrome and classic ToF, ToF with pulmonary atresia and multiple aorto-pulmonary collaterals, and ToF with absent pulmonary valve. Aorta hypoplasia was documented in one patient and suspected in another two. In half of these individuals, postoperative cardiac dysfunction was thought to be more severe than classic postoperative ToF repair. There may be an increase in right ventricular pressure, and right ventricular dysfunction due to free pulmonic regurgitation. Noncardiac developmental abnormalities in our series and the literature, including corectopia, heterochromia iridis, and congenital miosis suggest an underlying defect of neural crest cell migration in Myhre syndrome. We advise clinicians that Myhre syndrome should be considered in the genetic evaluation of a child with ToF, short stature, unusual facial features, and developmental delay, as these children may be at risk for increased postoperative morbidity. Additional research is needed to investigate the hypothesis that postoperative hemodynamics in these patients may be consistent with restrictive myocardial physiology.

Review of the Pathologic Characteristics in Myhre Syndrome: Gain-of-Function Pathogenic Variants in SMAD4 cause a Multisystem Fibroproliferative Response.

Background: Myhre syndrome, caused by pathogenic variants in SMAD4, is characterized by compact body habitus with short stature, distinctive craniofacial appearance, stiff skin, cardiovascular abnormalities (valve stenosis, coarctation, hypoplasia, or stenosis of aorta), effusions of potential spaces (pericardium, pleura, peritoneum), restricted movement of the joints (including thorax), and hearing loss. Lung and airway disease has been reported, but not always well-defined, to include interstitial lung disease, large airway obstruction, and pulmonary arterial hypertension. Excessive fibroproliferation of tissues especially following trauma or surgical instrumentation has been recognized, although these may also present spontaneously. Method: We report the pathologic features of 1 new patient with progressive choanal stenosis, and 22 literature cases, including the expanded history of 5 patients (3 who died). Results: Examination of patient tissues documents cellular fibroproliferation and deposition of excessive extracellular matrix explaining some of the observed clinical features of Myhre syndrome. Conclusion: Excessive fibrosis is noted in multiple tissues, especially heart, lung, and upper and lower airways. Our research provides the first systematic review to provide a knowledge base of gross and pathologic findings in Myhre syndrome.

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-ß 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.

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.

Myhre syndrome: A first familial recurrence and broadening of the phenotypic spectrum.

Myhre syndrome is a rare multisystem connective tissue disorder, characterized by short stature, facial dysmorphology, variable intellectual disability, skeletal abnormalities, arthropathy, cardiopathy, laryngotracheal anomalies, and stiff skin. So far, all molecularly confirmed cases harbored a de novo heterozygous gain-of-function mutation in SMAD4, encoding the SMAD4 transducer protein required for both transforming growth factor-beta and bone morphogenic proteins signaling. We report on four novel patients (one female proband and her two affected children, and one male proband) with Myhre syndrome harboring the recurrent c.1486C>T (p.Arg496Cys) mutation in SMAD4. The female proband presented with a congenital heart defect, vertebral anomalies, and facial dysmorphic features. She developed severe tracheal stenosis requiring a total laryngectomy. With assisted reproductive treatment, she gave birth to two affected children. The second proband presented with visual impairment following lensectomy in childhood, short stature, brachydactyly, stiff skin, and decreased peripheral sensitivity. Transmission electron microscopy (TEM) of the dermis shows irregular elastin cores with globular deposits and almost absent surrounding microfibrils and suggests age-related increased collagen deposition. We report on the first familial case of Myhre syndrome and illustrate the variable clinical spectrum of the disorder. Despite the primarily fibrotic nature of the disease, TEM analysis mainly indicates elastic fiber anomalies.

A child with Myhre syndrome presenting with corectopia and tetralogy of Fallot.

Myhre syndrome is a rare autosomal dominant disorder caused by a narrow spectrum of missense mutations in the SMAD4 gene. Typical features of this disorder are distinctive facial appearance, deafness, intellectual disability, cardiovascular abnormalities, short stature, short hands and feet, compact build, joint stiffness, and skeletal anomalies. The clinical features generally appear during childhood and become more evident in older patients. Therefore, the diagnosis of this syndrome in the first years of life is challenging. We report a 2-year-old girl diagnosed with Myhre syndrome by whole exome sequencing (WES) that revealed the recurrent p.Ile500Val mutation in the SMAD4 gene. Our patient presented with growth deficiency, dysmorphic features, tetralogy of Fallot, and corectopia (also known as ectopia pupillae). The girl we described is the youngest patient with Myhre syndrome. Moreover, corectopia and tetralogy of Fallot have not been previously reported in this disorder.

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

UNLABELLED: 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.

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.

Novel SMAD4 mutation causing Myhre syndrome.

Myhre syndrome (MYHRS, OMIM 139210) is an autosomal dominant disorder characterized by developmental and growth delay, athletic muscular built, variable cognitive deficits, skeletal anomalies, stiffness of joints, distinctive facial gestalt and deafness. Recently, SMAD4 (OMIM 600993) was identified by exome sequencing as the disease gene mutated in MYHRS. Previously only three missense mutations affecting Ile500 (p.Ile500Thr, p.Ile500Val, and p.Ile500Met) have been described in 22 unrelated subjects with MYHRS or a clinically related phenotype. Here we report on a 15-year-old boy with typical MYHRS and a novel heterozygous SMAD4 missense mutation affecting residue Arg496. This finding provides further information about the distinctive SMAD4 mutation spectrum in MYHRS. In silico structural analyses exploring the impact of the Arg-to-Cys change at codon 496 suggested that conformational changes promoted by replacement of Arg496 impact the stability of the SMAD heterotrimer and/or proper SMAD4 ubiquitination.

Myhre syndrome: a rare craniofacial disorder.

AIMS: Myhre syndrome is a rare disorder characterized by abnormal growth of the skeleton, muscles, and joints. The relationship of this syndrome to craniofacial growth and development is unknown. To the authors' knowledge, this is the first Japanese case ever studied. METHODOLOGY: At 10 years and 7 months of age, the patient was referred to the Department of Pediatric Dentistry in the authors' hospital, complaining of a dental problem. RESULTS: The craniofacial region exhibited a long lower face, high and narrowed palate with submucous cleft palate, maxillary constriction, prognathism, open bite, and crowding of the dental arch. Some of these morphological disorders could be affected by the functional manifestations of muscular hypertrophy of the cheek region, muscle tenseness, or the low position of the tongue. General disorders of muscular hypertrophy, thickened bones, and limited joint mobility are consistent with craniofacial findings of muscle tension in the cheek region, thickened calvarium, and limitation of temporomandibular joint movement. The submucous cleft palate and crown deformation of the mandibular central incisor may be affected by dysfunctions of SMAD4 signaling. CONCLUSIONS: Craniofacial growth and development is affected by the general characteristics of Myhre syndrome, and could be important in its diagnosis.

A Second Family with Myhre Syndrome Caused by the Same Recurrent SMAD4 Pathogenic Variation (p.Arg496Cys).

Introduction: Myhre syndrome (MS; OMIM #139210) is a rare connective tissue disorder presenting with cardiovascular, respiratory, gastrointestinal, and skeletal system findings. Fewer than 100 patients were reported until recently, and all molecularly confirmed cases had de novo heterozygous gain-of-function mutations in the SMAD4 gene. Dysregulation of the TGF-beta signaling pathway leads to axial and appendicular skeleton, connective tissue, cardiovascular system, and central nervous system abnormalities. Case Presentation: Two siblings, 12 and 9 years old, were referred to us because of intellectual disability, neurodevelopmental delay, and dysmorphic facial features. Physical examination revealed hypertelorism, strabismus, small mouth, prognathism, short neck, stiff skin, and brachydactyly. Discussion: With a clinical diagnosis of MS, the SMAD4 gene was analyzed via Sanger sequencing, and a heterozygous c.1486C>T (p.Arg496Cys) pathogenic variation was detected in both of the siblings. The segregation analysis revealed that the mutation was inherited from the father who displayed a milder phenotype. Among the 90 patients in the literature, one family was reported in which two siblings carried the same variation (p.Arg496Cys), inherited from the severely affected mother. We are reporting the second family which has three affected family members, a father and two children. We report this study to remind the clinicians to be aware of the parental transmission of SMAD4 variations and also evaluate the parents of the Myhre cases.

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.

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-ß 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.

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.