achondrogenesis

Achondrogenesis refers to a group of rare and extreme skeletal dysplasias.

Epidemiology

The estimated incidence is 1:40,000 with no recognized gender predilection.

Pathology

It is classified as an osteochondrodysplasia, meaning deficiency of both bone and cartilage development.

Subtypes

There are several recognized subtypes:

Genetics

Mutations in the SLC26A2 and COL2A1 genes cause achondrogenesis types 1B and 2, respectively. The genetic cause of achondrogenesis type 1A is still unknown. The patterns of inheritance are autosomal recessive in types 1A and 1B, and autosomal dominant with de-novo mutations in type B.

Radiographic features

Antenatal ultrasound

Sonographic diagnosis may be possible after 13 weeks of gestation, where nuchal edema may be evident as an early (though non-specific) sign.

The fetal bony structures are often unable to be identified. There may also be extreme micromelia . Calvarial ossification may be preserved with the type II subtype which can, in turn, give a floating head appearance.

Additional sonographic findings include:

Other ancillary sonographic features that may be present include:

Treatment and prognosis

The prognosis is generally poor, with most infants being stillborn or dying soon after birth.

History and etymology

M Fracaro first described a case of achondrogenesis in 1952.

Differential diagnosis

General considerations for mild cases include hypochondrogenesis. For absent calvarial bone(s) (type 1A/1B) on antenatal ultrasound, consider acrania.

See also

  • achondroplasia: a common cause of dwarfism; not to be confused with achondrogenesis