Images in Clinical Practice

Indian Pediatrics 2002; 39:694-695

Achondroplasia

A 4-year-old boy born to non-consanguineous parents was diagnosed to have achondroplasia by antenatal ultrasound. At birth, clinical examination revealed a term baby with large head, prominent forehead, depressed nasal bridge and short upper and lower limbs. His birth weight was 3 kg, length 47 cm and head circumference 40 cm. He also had mild hypotonia and short thoracic cage at birth. He had been followed up with serial head circumference measurements during infancy (Fig.1). At the age of 8 months he had rapidly increasing head circumference with wide and bulging anterior fontanel. A cranial ultrasound performed at that time revealed dilated lateral and third ventricles. A ventriculo peritoneal shunt was done at 8-months of age. Now, at the age of 4 years, his height is 75 cm (height age 1 year) and head circumference is 52 cm. His mental development and intelligence is normal for his age.

Fig. 1. Photograph at 3-months of age showing large head, depressed nasal bridge, prominent forehead and short limbs.

Achondroplasia is the most common chondrodysplasia occuring with the frequency of 1 in 15,000. It is an autosomal dominant disorder, but majority of the cases represent a fresh gene mutation. Older paternal age is a contributory factor. Children with achondroplasia have short stature, megalencephaly, small foramen magnum, depressed nasal bridge, prominent forehead and short limbs. The limbs shortening is greatest in the proximal segments and the fingers display a trident configuration. They have mild hypotonia and slow motor development but intelligence is usually normal. Prominent skeletal features are small cuboid shaped vertebral bodies with progressive narrowing of lumbar interpedicular distance and short tubular bones especially humerii. Hydrocephalus is one of the neurological complications that can occur in these children. Hence it is recommended that head circumference should be measured throughout infancy and plotted against norms published for achondroplastic individuals. Ultrasound studies of the brain should be considered if the fontanel size is large and head circumference increases rapidly. Mutation in the gene encoding fibroblast growth factor receptor 3 located at 4p16.3 has been shown to cause achondroplasia.