Achondroplasia is a congenital condition resulting from interference with enchondral ossification and is characterised by dwarfism of the short limb type, associated with a large head and, in many cases, so-called “ trident hands\".  It is the commonest type of dwarfism and perhaps the most ancient one.

 Dwarfing conditions are frequently referred to as short-limb or short-trunk types, according to whether the trunk or limbs are more extensively involved. Achondroplasia, hypochondroplasia, and metaphyseal chondrodysplasias are considered short-limb dwarfing conditions. These patients\' sitting height is within normal range. Additional terms used to describe the segment of the limb with the greatest involvement are rhizomelic (proximal), mesomelic (middle), and acromelic (distal). In achondroplasia, the extremity involvement is rhizomelic, with the arms and thighs more severely involved than the forearms, legs, hands, and feet.

Most cases-nearly 90 per cent. of the series studied by are sporadic.Achondroplasia occurs with equal frequency in males and females.A single gene mapped to the short arm of the fourth chromosome (band 4p16.3) is responsible for achondroplasia and is transmitted as an autosomal dominant trait.

Mutation in FGFR3 (Fibroblast growth factor receptor gene) is responsible for achondroplasia, hypochondroplasia, and thanatophoric dysplasia

The primary defect found in patients with achondroplasia is abnormal endochondral ossification.

 

Clinical presentation:

Short stature with-

1. Delayed motor development

2.Cranial enlargement ,intelligence level is within normal limits

3.Recurrent otitis media is common due to poor drainage of the eustachian tubes from underdevelopment of the midface, relative hypertrophy of tonsils and adenoids, and temporal bone abnormalities

4.Abnormal development of the base of the skull results in a foramen magnum that is smaller than in average individuals. Narrowing of the foramen magnum compresses the cervicomedullary region, causing symptoms of respiratory insufficiency

5.abnormal curvature of the spine (eg, kyphosis, lordosis, scoliosis) may be present

6.Sitting height, a reflection of trunk length, is within normal limits

 

Cause of Death:
1.In children younger than 4 years, death most commonly occurs due to brain stem compression, which causes sudden death.

2.In individuals aged 5-24 years, central nervous system and respiratory abnormalities are the common causes of death.

3.In persons aged 25-54 years, cardiovascular problems are the most frequent causes of death

 

The diagnosis is based on the typical clinical and radiologic features; the delineation from severe hypochondroplasia may be arbitrary.

A lateral skull radiograph demonstrates midface hypoplasia, enlarged calvaria, frontal prominence, and shortening of the base of the skull. The size of the foramen magnum is diminished

A lumbar spine (anteroposterior [AP]) view reveals distinct narrowing on the interpedicular distances from proximal to distal in L1-L5.Vertebral bodies reveal significant posterior scalloping.

Square shaped iliac wings(Elephant ears).acetabular roof is horizontal

Champagne glass pelvis.

The long bones have metaphyseal flaring and are short and thick.The distal femoral physes have an inverted-V (chevron) shaped configuration.

Short, broad neck of femur .

The fibula is typically longer than the tibia.