Achondroplasia

Roshni Sonawane
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Clinical Features of Achondroplasia
It does not have any predilection for any race or gender. The characteristic features at birth are macrocephaly, frontal bossing, midface retrusion, depressed nasal bridge, rhizomelic limb shortening, narrow trunk and trident hand. The FGFR3 gene abnormality confirmation is not necessary for the diagnosis. Infants present with mild to moderate hypotonia and delayed motor developmental milestones. They have difficulty holding head due to the combination of macrocephaly and hypotonia.
Rest of the clinical spectrum evolves secondary to the abnormal linear growth as follows:
Extremities: Hyper-extensibility occurs in most joints, especially the knee joints. However, there is a restriction of extension and rotation of the elbow. There is characteristic 'trident' deformity of the hand. Also, genu varum deformity is seen in many adults.
Spine: Various deformities of the spine can be seen in patients with Achondroplasia. Thoracolumbar gibbus is commonly present at birth. In few cases, it may fail to resolve spontaneously and lead to progressive neurologic sequelae in adulthood. Child carriers where sitting is unsupported, mechanical swings, jumpers and umbrella-style strollers are suspected to enhance the risk of gibbus. Exaggerated lumbar lordosis develops with the onset of ambulation. Patients may complain of back pain and muscle fatigue. Finally, worsening upper lumbar spinal stenosis presents in adulthood with intermittent back pain, sciatica, radical claudication and in extreme cases, loss of continence and lower limb function.
Growth: It is recommended to plot the growth parameters plotted on Achondroplasia-specific growth charts. These charts guide to identify individuals who vary from the norms for this population. Arm span, total body length, upper to lower body segment ratio, head circumference and weight can be observed. Body mass index is not a reliable parameter. Growth disorders associated with Achondroplasia are: A) Short stature: The short stature progressively predominates during childhood and later adulthood. The average adult height is 131+/-5.6 cm for men and 124 +/- 5.9 cm for women. B) Obesity: Mean weight in adults is 55 kg for males and 46 kg for females with a predisposition to obesity, which is a major problem in Achondroplasia. Excessive weight gain manifests since early childhood. In adulthood, obesity may worsen the aforementioned musculoskeletal problems like lumbar stenosis and occurrence of non-specific joint pains, increasing the disease morbidity. C) Failure to thrive may occur in infants and children with respiratory compromise.


Neurological:
Megalencephaly and Macrocephaly: Both true megalencephaly and macrocephaly are features of Achondroplasia. There is also narrowing of the foramen magnum which results in stenosis of the sigmoid sinus. This can elevate the intracranial venous pressure level and cause internal hydrocephalus.
Abnormalities at the craniocervical junction: Narrow craniocervical junction can also cause cervical cord compression. It may present with severe hypotonia, clonus, lower limb hyperreflexia, and central apnoea (confirmed on sleep studies).
Intelligence: It is unaffected in achondroplasia per say. However, it may be affected secondary to hydrocephalus or other central nervous system complication.


Respiratory problems secondary to the skeletal abnormalities in Achondroplasia: These can be categorized as: A) Relative adenoid and tonsillar hypertrophy due to mild mid-facial hypoplasia. B) Muscular upper airway obstruction associated with progressive hydrocephalus due to jugular foramen stenosis. C) Muscular upper airway obstruction due to hypoglossal canal stenosis (not associated with hydrocephalus). D) Chronic recurrent otitis media, predisposed by multiple anatomical factors like midfacial hypoplasia, eustachian tubes shortening, small pharynx and relative enlargement of tonsils and adenoids. E) Central apnoea from brainstem compression. F) Restrictive and obstructive pulmonary disease can also occur. G) Obstructive sleep apnoea is frequently seen in pediatric as well as adult age groups. It occurs secondary to the anatomical changes leading to shortening of upper airways.


References
Achondroplasia Achondroplasia 04/04/2016
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