Achondroplasia

Achondroplasia is the most common form of short-limbed dwarfism. It is characterized by short-limbed dwarfism, macrocephaly, frontal bossing, a low nasal bridge, and midface hypoplasia. Skeletal malformations may include brachydactyly, lordosis, genu varum, and/or stenosis of the spine. Additional abnormalities may include limited extension of the elbows and hips, hypotonia, and frequent otitis media. In most cases achondroplasia appears sporadically.

Achondroplasia appears to occur sporadically with no apparent family history. However, the possibility of familial transmission has been suggested, and inheritance as an autosomal dominant pattern with new dominant gene mutations has been reported. Advanced paternal age may be a contributing factor in cases of sporadic achondroplasia. In the absence of mutations, familial cases of achondroplasia have been reported as autosomal dominant inheritance but are much less common. Specific mutations of a gene known as fibroblast growth factor receptor (FGFR)-3 are possible. The FGFR-3 gene is located on chromosome 4 (4p16.3).

Achondroplasia is a rare genetic disorder characterized by macrocephaly, frontal bossing, and depressed nasal bridge. The arms and legs usually are very short, and the trunk appears long in comparison. Rhizomelic dwarfism, unusually prominent abdomen and buttocks, and short hands with fingers usually assuming a “trident" or three-pronged position during extension are characteristic. The trident position is described by an index and middle finger typically close together and the ring finger and the pinkie close together, giving the hand a three-pronged (trident) appearance. The hands are generally short and broad. Infants typically have an arched or vaulted skull in response to the megaloencephaly, which is pathognomonic of the syndrome. The forehead is broad. Midface hypoplasia can be seen. The presence of dorsal kyphosis adds to the dwarfism appearance. Hydrocephalus may be present, so the risk of elevated intracranial pressure should be remembered. Compression of the brainstem because of foramen magnum stenosis may occur in some children and result in a life-threatening condition. The respiratory system may be associated with upper airway obstruction because of midface hypoplasia and short neck. Other features include hearing loss secondary to chronic recurrent otitis media. The incidence of obstructive sleep apnea has been reported because of the macroglossia, high arched palate, prominent mandible, and choanal stenosis. Tonsilloadenoidectomy may improve the symptoms. The cardiovascular system is not involved in this disease. However, as a result of airway obstruction, secondary pulmonary artery hypertension and right ventricular hypertrophy may develop. Obesity may develop in both genders. The mean male adult height is 131 cm and the mean female height is 124 cm. Children may have deformities of the rib cage, including excessive curvature or “cupping” of the ribs. Intellectually, achondroplasia does not cause any impairment or deficiencies in mental abilities. The life expectancy of infants older than 12 months is normal.

The presence of normal intelligence and proper social skills for their age should be considered in the management of the children, adolescents, and adults with the disorder. The most important anesthetic consideration should be the airway. The presence of choanal atresia or stenosis and macroglossia could make face-mask ventilation difficult. Direct laryngoscopy usually is not limited because of the prominent mandible, but the limitation of cervical mobility may make visibility of the larynx difficult. Associated with the potential presence of raised intracranial pressure, compression of the brainstem, foramen magnum stenosis, and limited mobility at the C1-C2 junction, the preparation for airway management requires proper planning. Fifty percent of patients present with spinal involvement, so proper monitoring of the spinal cord is indicated for induction, positioning, and maintenance of anesthesia. Use of somatosensory evoked potential should be considered, especially with surgical procedure requiring special positioning or mobilization of the cervical spine. The importance of monitoring resides in the changes that occur over time in comparison to baseline. Patients affected with pulmonary hypertension or right ventricular hypertrophy should be assessed preoperatively with care and proper anesthesia management applied for these conditions. If obesity is severe, the potential risk of gastrointestinal reflux must be kept in mind. Positioning of the patient may be influenced by the joint contracture and limited mobility. Proper padding of pressure points must be ensured.

Hypochondroplasia is a genetic disorder characterized by short-limbed dwarfism. Short stature often is not recognized until early to middle childhood or even until adulthood in some cases. Affected individuals may develop bowing of the legs during early childhood that often improves spontaneously with age. Additional features include macrocephaly, forehead bossing, and limited extension and rotation of the elbows. Mild mental retardation may be present in approximately 10 percent of cases. Sporadic cases with no apparent family history have been described. However, the disorder is familial and seems to be inherited as an autosomal dominant pattern.