Brachyolmia

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

Orpha Number: 1293

Definition

Brachyolmia is a rare, clinically and genetically heterogeneous group of bone disorders characterized by short trunk, mild short stature, scoliosis and generalized platyspondyly without significant abnormalities in the long bones.

Epidemiology

The prevalence of brachyolmia is not known, but the disorder is probably under-recognized. Fewer than 100 cases have been reported to date. Cases have been reported in various ethnic groups. However, most cases with the Hobaek/Toledo type reported so far were of Turkish origin.

Clinical description

Four types of brachyolmia have been described: autosomal recessive brachyolmia, Hobaek/Toledo type, autosomal recessive brachyolmia-amelogenesis imperfecta syndrome, autosomal dominant brachyolmia, and autosomal recessive brachyolmia, Maroteaux type (see these terms). The age of onset is generally in childhood with short stature becoming more evident with age. The clinical manifestations are generally mild to moderate, with minor physical functional repercussions. Some patients report non-specific back pain. The disorder is not associated with intellectual disability. AR brachyolmia, Hobaek/Toledo type is characterized by short-trunked short stature with platyspondyly and scoliosis. Corneal opacities and precocious calcification of costal cartilage occur in rare cases. In AR brachyolmia-amelogenesis imperfecta syndrome, short-trunked short stature is associated with platyspondyly and enamel abnormalities. AD brachyolmia is a more severe form with significant short- trunked short stature, platyspondyly and kyphoscoliosis. Lastly, presumably autosomal recessive brachyolmia, Maroteaux type is a vague entity that has not been well characterized but may involve short trunk/short stature, generalized platyspondyly and rounding vertebral bodies.

Etiology

Mutations in the PAPSS2 gene (10q24) have been found in patients with AR brachyolmia, Hobaek/Toledo type, and in the TRPV4 gene (12q24.1) in patients with AD brachyolmia. Precise pathogenesis is not well understood.

Diagnostic methods

Clinical and radiological findings are used to diagnose brachyolmia. Molecular genetic testing can also be used to confirm the diagnosis.

Differential diagnosis

The differential diagnosis includes other genetic skeletal dysplasia syndromes, particularly mild spondyloepiphyseal dysplasia, including mild type 2 collagenopathy and mild Morquio disease (see this term).

Antenatal diagnosis

Prenatal diagnosis is available on molecular grounds, when a mutation (or mutations) was ascertained in a familial case.

Genetic counseling

Brachyolmia follows either an autosomal recessive or rarely an autosomal dominant pattern of inheritance. Genetic counseling based on the mode of inheritance should be provided to affected families.

Management and treatment

No specific treatment is currently available for this disease.

Prognosis

The prognosis for patients with brachyolmia is generally very good.

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