Achondrogenesie
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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:
- type 1
- type 1A: Houston-Harris subtype
- type 1B: Parenti-Fraccaro subtype
- type 2: Langer-Saldino achondrogenesis
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:
- micrognathia
- macrocephaly
- frontal bossing
- flat face
- anteverted nares
- long philtrum
- narrow fetal thorax
- lung aplasia/hypoplasia
- rib fractures may be present in type 1A
Other ancillary sonographic features that may be present include:
- polyhydramnios
- development of hydrops fetalis
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
Siehe auch:
- Achondroplasie
- Akranie
- fehlende enchondrale Ossifikation
- Achondrogenesie Typ IA
- Achondrogenesie Typ IB
- Achondrogenesie Typ II
und weiter:
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