Achondrogenèse

The achondrogenèse is a constitutional disease of the lethal bone E either In utero or a few days after the birth. It is the second constitutional disease of the bone lethal after the Nanisme thanatophore. The achondrogenèse is a nanism by generalized severe shortening of the members or Micromélie associated with small a trunk and an abnormally large cranium. There exist several types of achondrogenèse in connection with different genetic anomalies:

Standard IA: Standard Achondrogenèse Houston-Harris
Standard IB: Standard Achondrogenèse Fraccaro
Standard II: Standard Achondrogenèse Langer-Saldino or chondrogenesis imperfecta

The distinction is important because of the modes of transmission different involving from the different genetic councils

Type IB of achondrogenèse standard Fraccaro

Etiology

Change of the Gene SLC26A2 aqueous solution carrier family 26 (sulfate to transport), member 2 located on the Locus q31-q34 of the Chromosome 5.
The change of this gene is the only known genic change responsible for this disease.

Incidence

Unknown factor

Description

With the birth

The newborn present of the very short member S (it is most severe of the nanisms). With Finger S and shortened Toe S, a protuberant Abdomen and fatty aspect of the child by excess of soft fabric compared to the Skeleton. The cranium appears disproportionate in comparison with the body. The face is flat and the short neck. The death occurs rapidement.
The osseous radiography of the skeleton is essential to diagnose with certainty of the others constitutional lethal diseases of the bone.

With echography

There exists an excess of Amniotic liquid (Hydramnios). The Biometrics of the Os watch which them size is very in lower part of the curve of normal growth. The echogenicity of the bones is weak especially that of the spinal column and cranium. An early diagnosis can be made as of the 10^e week in the event of antecedents of achondrogenèse.

Diagnosis

The certainty of the diagnosis requires the histological study of the Cartilage S and the bone of new-né.
The diagnosis can be made by the research of the change S of gene SLC26A2. There exist five genic changes person in charge of this disease. This research is positive only in 65% of the cases, obliging a total analysis of gene to establish the diagnosis.

Differential diagnosis

The differential diagnosis with the others Ostéochondrodysplasie S lethal is sometimes difficult. A precise diagnosis requires:

of the precise Radiography S and good quality
of fabric allowing a genetic study
a cutaneous Biopsy allowing a Culture of fibroblast
a sample of the cartilage and histological bones for studies and biochimiques

Principal pathologies to be discussed are:

imperfect Osteogenesis standard II and III
Nanisme thanatophore
Syndrome coasts short Polydactylies standard I, II, and III
Fibrochondrogenèse
Achondroplasie in the form homozygote

Mode of transmission

Recessive autosomic transmission

Prenatal diagnosis

Echography makes it possible to detect an affected fetus precociously. The diagnosis is also possible by genic study if the changes of the two parents are known.

The genetic Council

The two parents of a fetus or child carrying this pathology are always carrying a transferred gene. They do not have any clinical demonstration and the disease risk osseous is not augmenté.
The risk to have new born affected is of 25%.

Type IA of achondrogenèse or standard Houston-Farry

Etiology

Unknown gene

Mode of transmission

Recessive Autosomique

Type II of achondrogenèse or Standard Lander-Saldino or imperfect chondrogenesis

Etiology

Change of the gene COL2A1 collagen, type II, alpha 1 located on the Locus q13.1-q13 of the Chromosome 12.
This change is always a change of novo .

Mode of transmission

Autosomique dominating E

Sources

Site of information on the orphan rare diseases and drugs
Online Mendelian Inheritance in Man, OMIM (TM). Johns Hopkins University, Baltimore, MANDELEVIUM. MIM Number: 600972 * GeneTests: Medical Genetics Information Resource (database online). Copyright, University off Washington, Seattle. 1993-2005

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