Axial spondylometaphyseal dysplasia

Alternate names

Axial SMD; Spondylometaphyseal dysplasia axial type; SMD Axial

Definition

Axial spondylometaphyseal dysplasia is a genetic disorder of bone growth. The term “axial” means towards the center of the body. “Sphondylos” is a Greek term meaning vertebra. “Metaphyseal dysplasia” refers to abnormalities at the ends of long bones.

Cause

The underlying genetic cause of axial spondylometaphyseal dysplasia is currently unknown.

Inheritance

Autosomal recessive inheritance, a 25% chance

It is thought to be inherited in an autosomal recessive fashion.

Signs and symptoms

• Common signs and sympotms of axial spondylometaphyseal dysplasia, include short stature, chest, spine, limb, and pelvic bone changes, and vision disturbance.
• People with axial spondylometaphyseal dysplasia may have a normal birth length, but demonstrate growth failure by late infancy to early childhood.
• A measurement called standard deviation (SD) is used to compare the height of different children.
• If a child's height is more than 2 SD's below the average height of other children the same age, the child is said to have short stature.
• This means that almost all of the other children that age (more than 95% or 19 out of 20) are taller.
• Individual case reports of children and an adult with axial spondlometaphyseal dysplasia demonstrate height as being between 2 to 6 SD’s below average.
• Infants with axial spondlometaphyseal dysplasia tend to have a shortened chest with short ribs, a condition called thoracic hypoplasia.
• Thoracic hypoplasia tends to become more prominent in childhood, and less noticeable in adolescence and adulthood.
• Thoracic hypoplasia may cause mild to moderate breathing problems in infants and recurring lung infections in childhood.
• Spine changes include vertebrae that have a flattened appearance on x-ray.
• This finding is typically mild in infancy and early childhood, becomes more apparent in late childhood, then self-corrects by adulthood.
• Some individuals with axial spondylometaphyseal dysplasia develop scoliosis (curvature of the spine).
• Pelvic bone changes can be seen in infants and children. Some of these changes self-correct by adulthood.
• A condition called “coxa vara” (where the angle between the top of the femur and the femoral shaft is smaller than normal) is common beginning in late childhood and persists through adulthood.
• Coxa vara may affect gait (pattern or way of walking).
• Some people with axial spondlometaphyseal dysplasia have minor bone changes in their knees.
• Vision problems, including retinitis pigmentosa and/or optic atrophy, become evident in infancy or early childhood and rapidly worsen.
• Retinitis pigmentosa causes cells in the retina to breakdown and die, eventually resulting in vision loss.
• Optic atrophy causes vision to dim and reduces the field of vision.
• It also reduces the ability to see fine detail and color (ie., colors will seem faded). With the progression of optic atrophy, a person's pupil reaction to light diminishes and may eventually be lost.
• Long term outlook for vision for people with axial spondylometaphyseal dysplasia is poor.

Treatment

• There is no specific treatment for axial spondylometaphyseal dysplasia.
• Symptoms such as lung infections, breathing difficulties, coxa vara, scoliosis, retinitis pigmentosa, and optic atrophy are managed individually.
• Specialists such as opthmologists, geneticists, and orthopedists work in concert in devloping an individualized treatment plan.
• We are unaware of any cases describing the use of growth hormone therapies for treatment of short stature caused by axial spondylometaphyseal dysplasia. Treatment of skeletal dysplasias with growth hormone therapy must be done with caution.

NIH genetic and rare disease info

• NIH info on Axial spondylometaphyseal dysplasia

Axial spondylometaphyseal dysplasia is a rare disease.

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