Clinical characteristics: The autosomal dominant TRPV4 disorders (previously considered to be clinically distinct phenotypes before their molecular basis was discovered) are now grouped into neuromuscular disorders and skeletal dysplasias; however, the overlap within each group is considerable. Affected individuals typically have either neuromuscular or skeletal manifestations alone, and in only rare instances an overlap syndrome has been reported.
The three autosomal dominant neuromuscular disorders (mildest to most severe) are:
Charcot-Marie-Tooth disease type 2C
Scapuloperoneal spinal muscular atrophy
Congenital distal spinal muscular atrophy
The autosomal dominant neuromuscular disorders are characterized by a congenital-onset, static, or later-onset progressive peripheral neuropathy with variable combinations of laryngeal dysfunction (i.e., vocal fold paresis), respiratory dysfunction, and joint contractures.
The six autosomal dominant skeletal dysplasias (mildest to most severe) are:
Familial digital arthropathy-brachydactyly
Autosomal dominant brachyolmia
Spondylometaphyseal dysplasia, Kozlowski type
Spondyloepiphyseal dysplasia, Maroteaux type
The skeletal dysplasia is characterized by brachydactyly (in all 6); the five that are more severe have short stature that varies from mild to severe with progressive spinal deformity and involvement of the long bones and pelvis. In the mildest of the autosomal dominant TRPV4 disorders life span is normal; in the most severe it is shortened.
Bilateral progressive sensorineural hearing loss (SNHL) can occur with both autosomal dominant neuromuscular disorders and skeletal dysplasias.
Diagnosis/testing: The diagnosis of an autosomal dominant TRPV4 disorder is established in a proband with characteristic clinical and neurophysiologic findings, radiographic findings in the skeletal dysplasias, and a heterozygous TRPV4 pathogenic variant identified on molecular genetic testing.
Management: Treatment of manifestations: Treatment is focused on symptom management. Affected individuals are often evaluated and managed by a multidisciplinary team that may include neurologists, physiatrists, orthopedic surgeons, and physical and occupational therapists. SNHL is managed by specialists to determine the best management options.
For neuromuscular disorders, neuropathy and respiratory dysfunction are managed in a routine manner; individuals with laryngeal dysfunction require ENT evaluation that should include speech therapy, laryngoscopy, and, in some instances, surgery.
For skeletal dysplasias, physical therapy/exercise and heel-cord stretching to maintain function; surgical intervention when kyphoscoliosis compromises pulmonary function and/or causes pain and/or when upper cervical spine instability and/or cervical myelopathy are present.
Surveillance: For neuromuscular disorders, annual neurologic examinations, physical therapy assessments, ENT monitoring of laryngeal function, dynamic breathing chest x-ray, and hearing assessment. For skeletal dysplasias, annual evaluation for joint pain and scoliosis; assessment for odontoid hypoplasia before a child reaches school age and before surgical procedures involving general anesthesia; annual hearing assessment.
Agents/circumstances to avoid: For neuromuscular disorders, obesity, as it makes walking more difficult; diabetes; medications that are toxic or potentially toxic to persons with a peripheral neuropathy. For skeletal dysplasias, extreme neck flexion and extension (in those with odontoid hypoplasia); activities that place undue stress on the spine and weight-bearing joints.
Pregnancy management: Ideally a woman with TRPV4 disorder would seek consultation from a high-risk OB-GYN or maternal-fetal medicine specialist to evaluate risk associated with pregnancy and delivery.
Genetic counseling: TRPV4 disorders are inherited in an autosomal dominant manner. Most individuals diagnosed with an autosomal dominant TRPV4 disorder have an affected parent. However, since the most severe skeletal phenotypes can be lethal in childhood (or in utero), children with these phenotypes likely have a de novo pathogenic variant and unaffected parents. Each child of an individual with an autosomal dominant TRPV4 disorder has a 50% chance of inheriting the pathogenic variant. Specific phenotype, age of onset, and disease severity cannot be predicted accurately because of reduced penetrance and variable expressivity. However, in general, a child who inherits a TRPV4 pathogenic variant associated with neuromuscular disease or skeletal dysplasia from an affected parent is likely to have the same phenotype as the parent. Prenatal and preimplantation genetic testing are possible if the pathogenic variant has been identified in an affected family member.
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