Achondroplasia and dental considerations

[drsnehamaheshwari]

Achondroplasia is the most common form of skeletal dysplasia dwarfism that manifests with stunted stature and disproportionate limb shortening. It occurs in 1 of 25,000 births. It is inherited as an autosomal dominant trait; however, 80% of the cases are sporadic. Achondroplasia is caused by mutation in fibroblast growth factor 3 (FGFR3) on chromosome 4, causing a defect in the maturation of chondrocytes in the cartilage growth plate which enables abnormal cartilage growth-plate differentiation and insufficient bony development. Prenatal diagnosis of achondroplasia is usually suspected on routine ultrasound with the image of shortened long bones and can be confirmed by molecular testing (FGFR3 mutational testing) of prenatal specimens. The diagnosis can usually be made on the basis of clinical characteristics and specific features on radiographs. Clinical features of achondroplasia include disproportionate short stature with normal trunk length, rhizomelic (the proximal end) shortening of the extremities, bowing of the lower extremities, short stubby trident hands (increased space between the third and the fourth fingers), spinal stenosis and lumbar lordosis (curved lower spine). Craniofacial characteristic of this disorder include macrocephaly, prominent forehead, depressed nasal bridge, maxillary hypoplasia, otolaryngeal system dysfunction, and foramen magnum stenosis. These characteristics may lead to number of complications including hydrocephalus, apnea, upper-airway obstruction, otitis media, sinusitis and dental malocclusion. Other complications may include obesity and diabetes. There is no cure for this disease, however, extended limb lengthening has been used to improve stature. Growth hormone therapy may result in a transient increase in growth rate but not effective in significantly increasing stature

Dealing with achondroplastic children needs special psychological management during dental treatment, as the presence of disproportionate short stature can cause a number of psychosocial and social problems. Presence of little stature and short limbs, in addition to chronic backache makes it hard for achondroplastic patient to sit comfortably on a conventional dental chair. Backache indicates spinal stenosis which is usually noticeable at late childhood and early adolescence. Lowering the dental chair and the use of step stool will help the achondroplastic child to get on the dental chair easily. A cushion behind the child’s back may be required during dental treatment for good posture and to reduce back pain. it is advised to perform dental treatment under local anesthesia, because general anesthesia poses certain complications due to anteriorly placed epiglottis, small nasal pharynx and larynx, difficulty in intubation, lumbar lordosis, narrowing of spinal cord and small chest. It is important for dental professionals, including pediatric dentists, orthodontists and oral surgeons treating these patients, to recognize risk factors and potential complications before sedation or anesthesia. When dental treatment is decided to be under GA, it is recommended todo radiologic evaluation of foramen magnum, preoxygenation before anesthesia, using appropriate endotracheal tube size, oral intubation and administration of oxygen after extubation

        

[drsnehamaheshwari]

Achondroplasia has recently been shown to result from a Gly to Arg substitution in the transmembrane domain of the fibroblast growth factor receptor 3 (FGFR3). By substituting the transmembrane domain of the Neu receptor tyrosine kinase with the transmembrane domains of wild-type and mutant FGFR3, the Arg380 mutation in FGFR3 is shown to activate both the kinase and transforming activities of this chimeric receptor. Residues with side chains capable of participating in hydrogen bond formation, including Glu, Asp, and to a lesser extent, Gln, Hisand Lys, are able to substitute for the activating Arg380 mutation. The Arg380 point mutation also causes ligand-independent stimulation of the tyrosine kinase activity of FGFR3 itself, and greatly increased constitutive levels of phosphotyrosine on the receptor. As a result, it limits the formation of bone from cartilage (a process called calcification), particularly in long bones. FGFR3 also plays an important role in cell growth and division, determination of cell type, formation of blood vessels, wound healing and embryo development.

In heterozygous state, achondroplasia is non-lethal with normal life span and normal intelligence. However, they are at risk like cervicomedullary compression (compression of the upper spinal cordat the base of the brain), spinal stenosis, obesity, obstructive sleep problem. In homozygous state, achondroplasia is a lethal condition in the early few months of life because of severe rib cage deformity that results in respiratory insufficiency. 

        

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