Achondrogenesis, Type IB; ACG1B

What is Achondrogenesis, Type IB; ACG1B?

Achondrogenesis, Type IB; ACG1B is a rare disease. It is also known as Achondrogenesis, Fraccaro Type Houston-Harris type achondrogenesis Parenti-Fraccaro type achondrogenesis.

Achondrogenesis type 1 (Parenti-Fraccaro type) and type 2 (Langer-Saldino type) cannot be distinguished clinically. Both result in stillbirth (or neonatal death) and are characterised by severe micromelia, a relatively large head, a short neck, a short trunk and a protuberant abdomen. Both have a flat nasal bridge and the whole nose is short with anteverted nostrils. Radiologically, ossification of the skull, spine and pelvis is more deficient in type 1 than in type 2. The long bones are more severely micromelic in type 1 and there are spiky metaphyseal spurs in both, but more so in type 1. Type 1 has been subdivided into types A (Houston-Harris type) and B (Parenti-Fraccaro type) (Kozlowski et al., 1978). Type 1-A cases have multiple rib fractures and almost complete lack of ossification of the spine. Chen et al., (1996) reported a case with features of type 1A with a posterior encephalocele.

It has been suggested that the cartilage matrix deficiency (cmd) mouse, which is caused by a mutation in the aggrecan gene, may be homologous to a form of human achondrogenesis (Watanabe et al., 1994).
Superti-Furga (1994) demonstrated that core protein and side chains of proteoglycans were not sulphated in a patient with type 1B. A defect of biologic activation of sulphation, leading to defective sulphation of macromolecules, was postulated. Superti-Furga et al., (1996) demonstrated mutations in the diastrophic dysplasia sulphate transporter gene (DTDST) in six patients with achondrogenesis type 1B. Cai et al., (1998) reported mutations in a further 17 week old fetus.
Fryns et al., (1994) mention a possible case with a de novo balanced 4q23;11q13 translocation. Unfortunately no clinical photographs or radiographs were shown. Superti-Furga (1996) provides a good review of the clinical, histological, and molecular aspects of achondrogenesis type 1B.
Karniski et al., (2001) studied genotype/phenotype correlation in DTDST mutations in diastrophic dysplasia, atelosteogenesis type II, and anchondrogenesis type1B. Individuals with achondrogenesis type 1b tend to be homozygous for null mutations whereas achondrogenesis type II patients have at least 1 allele with a loss of function mutation and diastrophic patients are homozygous for mutations with residual sulphate transport function.
TRIP11 Mutations in 1A have been found by Smits et al., (2011), in 10 unrelated patients Dizygotic twins both with type 1A were reported by Grigelioniene et al., (2013). Both had TRIP11 mutations. A third patient in the same report had a milder phenotype withnormal face, narrow thorax, short limbs, small hands and short fingers. He was a compound heterozygote for a nonsense mutation and a deletion at the 3' end of TRIP11.

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* This information is courtesy of the L M D.

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What gene changes cause Achondrogenesis, Type IB; ACG1B?

The syndrome is inherited in the following inheritance pattern/s:

Autosomal Recessive - Autosomal recessive inheritance means an affected individual receives one copy of a mutated gene from each of their parents, giving them two copies of a mutated gene. Parents, who carry only one copy of the gene mutation will not generally show any symptoms but have a 25% chance of passing the copies of the gene mutations onto each of their children.

In some cases, a genetic syndrome may be the result of a de-novo mutation and the first case in a family. In this case, this is a new gene mutation that occurs during the reproductive process.

OMIM Number - 600972 (please check the OMIM page for updated information)

The syndrome can be caused by mutations in the following gene/s location/s:
SLC26A2 - 5q32

What are the main symptoms of Achondrogenesis, Type IB; ACG1B?

The typical symptoms of the syndrome are:
Abnormality of the ribs, Aplasia/Hypoplasia of the lungs, Breech presentation, Polyhydramnios, Absent or minimally ossified vertebral bodies, Short thorax, Flat face, Frontal bossing, Skeletal dysplasia, Umbilical hernia, Macrocephaly, Stillbirth, Talipes, Respiratory failure, Short neck, Thickened nuchal skin fold, Autosomal recessive inheritance, Short toe, Short ribs, Hypoplastic ilia, Short stature, Hydrops fetalis, Malar flattening, Brachydactyly, Cystic hygroma, Edema, Neonatal short-limb short stature, Malformation of the heart and great vessels, Abnormality of bone mineral density, Abdominal distention, Micrognathia, Micromelia, Anteverted nares, Narrow chest, Short nose, Long philtrum, Inguinal hernia

How does someone get tested for Achondrogenesis, Type IB; ACG1B?

The initial testing for Achondrogenesis, Type IB; ACG1B can begin with facial genetic analysis screening, through the FDNA Telehealth telegenetics platform, which can identify the key markers of the syndrome and outline the type of genetic testing needed. A consultation with a genetic counselor and then a geneticist will follow.

Based on this clinical consultation with a geneticist, the different options for genetic testing will be shared and consent will be sought for further testing.

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