What is Acromicric Skeletal Dysplasia: Causes, Symptoms, Treatment, Diagnosis

What is Acromicric Skeletal Dysplasia?

Acromicric Skeletal Dysplasia is a very rare inherited disorder (bone dysplasia) affecting normal bone growth. It is believed to be caused by mutations in the FBN1 gene and inherited in an autosomal dominant manner. Here “Autosomal” means the gene is a non-sex chromosome and “Dominant” means that a single copy of the mutated gene is enough to cause the disease. An affected parent has a 50% chance to pass the condition to his/her children. Acromicric Skeletal Dysplasia affected children are generally two standard deviations or more below their normal height along with short hands, feet, and mild facial abnormalities. Intelligence is not affected; hence Acromicric Skeletal Dysplasia patients do not face any learning difficulties. Apart from stunted growth, no major complications appear.

Signs and Symptoms of Acromicric Skeletal Dysplasia

Acromicric Skeletal Dysplasia generally appears during late infancy showing features like short hands and feet. Certain bones in limbs are abnormally short. Thigh bone may have malformation.

By early childhood, the growth retardation turns into dwarfism. Individuals affected with Acromicric Skeletal Dysplasia reach an average height of about 4 feet (120 cm) [1].Infants suffering from Acromicric Skeletal Dysplasia may have an abnormally narrow opening between the eyelids and a short nose with anteverted nostrils. Distinctive facial abnormalities fade away as the child grows older.

Acromicric Skeletal Dysplasia patients may suffer from frequent ear, tracheal, and respiratory infection. In severe cases, spinal problems like curving, bowing or stenosis of the spine occurs.

Intelligence is not affected by this condition. Acromicric Skeletal Dysplasia patients generally have a normal life expectancy.

Causes of Acromicric Skeletal Dysplasia

Acromicric Skeletal Dysplasia is caused by the mutation in the FBN1 gene. This gene is responsible for making a giant protein called fibrillin-1. Molecules of fibrillin-1 attract each other and other proteins in an extracellular matrix (lattice of proteins between cells) to form microfibrils [2]. These microfibrils give strength and flexibility to connective tissues. They store growth factors in them, which they release at regular intervals for growth and repair of tissues and organs throughout the body. Mutations in the FBN1 gene make faulty microfibrils, which are responsible for the abnormalities in the skeletal system.

Epidemiology of Acromicric Skeletal Dysplasia

Acromicric Skeletal Dysplasia is inherited in autosomal dominant pattern. This means that even if one of the parents has a faulty gene, the child can get the disorder. New mutations in the gene are also very common, as most patients have no history of the disorder in their family. Males and females are equally affected. However, only a very few cases have been reported across the world.

Diagnosis of Acromicric Skeletal Dysplasia

Diagnosis of genetic disorders is very challenging. Acromicric Skeletal Dysplasia can be diagnosed by clinical testing, characteristic physical feature like short feet, and patient history. Imaging techniques like computerized tomography scans (CT), Magnetic Resonance Imaging (MRI) or X-rays are done to see internal body structures like bones.

Prenatal diagnostic imaging like ultrasound can detect shortened skeletal systems. Genetic testing is performed to identify genetic disorders, but it is quite expensive. X-rays can reveal typical bone abnormalities in arms and legs. The biopsy can reveal abnormalities in cartilage growth, like collagen formation in tendons and connective tissue.

Treatment of Acromicric Skeletal Dysplasia

Since symptoms vary from person to person, symptomatic treatment is usually done for Acromicric Skeletal Dysplasia. A specialized team effort of Paediatricians, who are specialists in the diagnosis and treatment of bone abnormalities, orthopedic surgeons, physiotherapists, and other health professionals, is required for childcare. Genetic counseling is beneficial for affected families.

Although growth hormone therapy (GH) has not been used for this particular disorder, the efficacy of GH in other types of skeletal dysplasia has been studied. For some disorders, GH had a significant effect on height gain, but not so much in others. It was concluded that GH therapy was moderately effective for height gain [3]. Application of GH therapy in Acromicric Skeletal Dysplasia after proper medical consultation can prove to be successful.

Surgical options are also there for treating Acromicric Skeletal Dysplasia. Since the patients suffer from chronic ear infections, draining tubes can be inserted in the middle ear to prevent hearing loss. Tracheotomy can be helpful for Acromicric Skeletal Dysplasia patients with breathing difficulty. Most of the patients suffer from spinal cord deformation. The spinal canal can be surgically widened to relieve pressure from the spinal cord. Neurosurgery can solve spinal stenosis, spinal instability, and hydrocephalus.

Exercise routines can be recommended to improve postural deformities like bowleg, flatfoot, and so on.

Prognosis of Acromicric Skeletal Dysplasia

The prognosis for people suffering from Acromicric Skeletal Dysplasia is generally good as there are almost negligible chances of complications. Most of the patients live a relatively normal life. The life expectancy of affected individuals is also normal.

Conclusion

Acromicric Skeletal Dysplasia is an extremely rare skeletal disorder. Most of the cases have occurred sporadically even without a family history. Prenatal tests can successfully predict such occurrences. Treatments are symptom specific. Fortunately, it is not lethal. No complications arise and most of the patients live fairly normal lives.

References:  

  1. de Bruin, C., Finlayson, C., Funari, M., Vasques, G., Lucheze Freire, B., & Lerario, A. et al. Two Patients with Severe Short Stature due to a <b><i>FBN1</i></b> Mutation (p.Ala1728Val) with a Mild Form of Acromicric Dysplasia. Hormone Research In Paediatrics, (2016). 342-348. doi: 10.1159/000446476.
  2. Faivre, L. Acromicric dysplasia: long term outcome and evidence of autosomal dominant inheritance. Journal Of Medical Genetics, (2001). 745-749. doi: 10.1136/jmg.38.11.745
  3. https://www.ncbi.nlm.nih.gov/pubmed/12928832

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