The Musculoskeletal Phenotype of the RASopathies
The Ras/MAPK signal transduction pathway is critical for the regulation of proliferation and differentiation of multiple cell types. Neurofibromatosis type 1 (NF1) is caused by inactivating mutations in the NF1 gene resulting in an increased Ras signaling cascade. Subsequently, additional syndromes with some overlapping physical manifestations such as Noonan syndrome, Costello syndrome, and cardiofaciocutaneous (CFC) syndrome were also shown to be due in many cases to mutations in genes encoding for proteins interacting with the Ras/MAPK pathway. Although neurocutaneous manifestations have been considered hallmark features for these disorders, multiple organ systems including the musculoskeletal system are affected. Some of the overlapping musculoskeletal phenotypes include scoliosis, kyphosis, anterior chest wall anomalies, pes planus, osteopenia, and hand anomalies. However, there are also discordant skeletal phenotypes such as sphenoid wing dysplasia and tibial pseudarthrosis seen only in NF1. We provide an overview of the concordant and discordant musculoskeletal manifestations in the RASopathies.
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- "All eight had low bone mineral density with the majority meeting a clinical diagnosis of osteoporosis [White et al., 2005]. Individual case studies noted hip contractures, hip dysplasia, ulnar deviation, hypotonia, lordosis and dysfunctional gait [Stevenson and Yang, 2011]. Although orthopedic issues have not been extensively studied in Costello syndrome, it is not because they are of little concern. "
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ABSTRACT: Costello syndrome is a rare genetic condition caused by heterozygous alterations in HRAS and characterized by multi-system abnormalities. Individuals with Costello syndrome usually present with severe feeding difficulties in infancy, short stature, coarse facial features, increased tumor risks, cardiac and neurological complications, intellectual disability and orthopedic complications. This study further defines the orthopedic manifestations affecting individuals with Costello syndrome. We studied 43 participants and performed medical records review, clinical examinations and orthopedic inquiry forms. In 23 participants, hip and or spinal imaging assessments were completed. Serial radiographs were analyzed when available. A total of 25 orthopedic manifestations were identified. Ten manifestations were seen in the majority of the participants: hypotonia (87%), ligamentous laxity (85%), scoliosis (63%), kyphosis (58%), characteristic hand deformities (85%), ulnar deviation of the wrist (63%), elbow (55%) and shoulder contractures (65%), tight Achilles tendon (73%), and pes planus (53%). Other characteristics of special note were hip dysplasia (45%), foot deformities requiring surgical intervention (38%) and osteopenia/osteoporosis (47%). We also studied the development of the hips and spine. Uni- or bilateral hip dysplasia was congenital in some, while it developed throughout childhood in others. Spinal involvement included scoliosis, kyphosis, lordosis, and curvature reversal (thoracic lordosis and lumbar kyphosis). Based on these findings, we recommend routine referral to an orthopedic surgeon as well as instituting screening protocols for hips and spine for individuals with Costello syndrome. © 2013 Wiley Periodicals, Inc.
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ABSTRACT: Costello syndrome (OMIM# 218040) is a distinctive rare multisystem disorder comprising a characteristic coarse facial appearance, intellectual disabilities, and tumor predisposition. Although the diagnosis can be suspected clinically, confirmation requires identification of a heterozygous mutation in the proto-oncogene HRAS. In contrast to somatic oncogenic mutations in neoplasia, the Costello syndrome changes are typically introduced in the paternal germline. The predicted amino acid substitutions allow for constitutive or prolonged activation of the HRAS protein, resulting in dysregulation of the Ras/mitogen activated protein kinase pathway. Dysregulation of this signaling pathway is the disease mechanism shared among Costello syndrome and other rasopathies, including neurofibromatosis type 1, Noonan syndrome, cardio-facio-cutaneous syndrome, and Legius syndrome. The Ras/mitogen activated protein kinase pathway governs cell proliferation and differentiation, and its dysregulation affects cardiac and brain development, accounting for the significant overlap in physical and developmental differences and common medical problems among rasopathies. Unlike the genetically heterogeneous Noonan syndrome and cardio-facio-cutaneous syndrome, Costello syndrome is caused by HRAS mutations only. Patients, clinicians, and researchers may benefit from a multidisciplinary "rasopathy clinic," which serves patients with more common conditions such as Noonan syndrome and neurofibromatosis and those affected by rare conditions such as Costello syndrome.
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