Brachyolmia type 3

The following summary is from Orphanet, a European reference portal for information on rare diseases and orphan drugs.

Orpha Number: 93304

Definition

A relatively severe form of brachyolmia, a group of rare genetic skeletal disorders, characterized by short-trunked short stature, platyspondyly and kyphoscoliosis. Degenerative joint disease (osteoarthropathy) in the spine, large joints and interphalangeal joints becomes manifest in adulthood.

Epidemiology

The precise prevalence of this form of brachyolmia is not known. About 30 cases have been reported.

Clinical description

Patients with Brachyolmia type 3 generally have a normal birth weight and length. Affected individuals present with moderately short trunk/short stature and mildly short limbs in childhood. Kyphoscoliosis is common and sometimes severe. Adult patients develop degenerative joint disease in the spine, large joints and small joints of the hands and feet, which may cause significant musculoskeletal morbidity, such as chronic pain in the extremities and spine, and paresthesia. Final adult height is reported to be 155-168 cm (males) and 136-150 cm (females). The radiographic features include severe platyspondyly particularly in the cervical spine, elongated vertebral bodies (overfaced pedicles), broad ilia, and mild metaphyseal irregularity in the proximal femora. Carpal ossification may be mildly delayed, and mild brachydactyly may exist.

Etiology

Heterozygous mutations in the TRPV4 gene (12q24.11) are responsible for autosomal dominant brachyolmia. TRPV4 mutations are associated with other skeletal dysplasias, including lethal and nonlethal metatropic dysplasia, spondyloepiphyseal dysplasia Maroteaux type, and spondylometaphyseal dysplasia Kozlowski type (see these terms). Autosomal dominant brachyolmia falls into the mildest end of the TRPV4 -associated skeletal dysplasia group. TRPV4 encodes a Ca-permeable, non-selective cation channel that participates in the regulation of osmotic sensitivity and mechanosensitivity. It remains to be explained how dysregulation of the cation channel causes the skeletal abnormalities.

Genetic counseling

Genetic counseling should be provided to affected families, in consideration of the autosomal dominant mode of inheritance.

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