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Achondrogenesis, Type II; ACG2
What is Achondrogenesis, Type II; ACG2?
Achondrogenesis, Type II; ACG2 is a rare disease. It is also known as Achondrogenesis, Langer-saldino Type Achondrogenesis, Type Ib, Formerly Chondrogenesis Imperfecta Langer-Saldino 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. Rittler and Orioli (1995) reported a case with postaxial polydactyly and Wainwright and Beighton (2008) a case with cutaneous hamartomas (hairless, papillomatous).
Achondrogenesis type 2 probably represents the most severe end of the spectrum of the group of conditions including hypochondrogenesis and spondylo-epiphyseal dysplasia congenita. Defects of type II collagen synthesis have been demonstrated in some cases (Eyre et al., 1986; Horton et al., 1987) and it seems likely that most cases are caused by new dominant mutations. Mortier et al., (1995) demonstrated a single base change that resulted in the substitution of glycine by arginine in the triple helical domain. Körkkö et al., (2000) reported further mutations in the COL2A1 gene.
Soothill et al., (1993) reported a case diagnosed by transvaginal ultrasound at 12 weeks gestation. The case picked up prenatally by Kocakoc and Kiris (2002) by ultrasound, and with normal long bones, most certainly does not have this condition. It probably has a form of spondylocostal dysostosis (qv). Of great importance are the 2 affected fetuses (one with a heterozygous mutation, the other could not be tested), born to parents without the mutation, suggesting mosaicism (Faivre et al., 2004). The family of 3 affected fetuses reported by Forzano et al., (2007) had a father with childhood scoliosis and mild flattening and anterior wedging of vertebral bodies. He was shown to be a mosaic for the mutation found in the sibs. Further examples of mosaicism were provided by Comstock et al., (2010).
* This information is courtesy of the L M D.
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What gene changes cause Achondrogenesis, Type II; ACG2?
The syndrome is inherited in the following inheritance pattern/s:
Autosomal Dominant - In the case of autosomal dominant inheritance, just one parent is the carrier of the gene mutation, and they have a 50% chance of passing it onto each of their children. Syndromes inherited in an autosomal dominant inheritance are caused by just one copy of the gene mutation.
Sporadic - 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.
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 - 200610 (please check the OMIM page for updated information)
The syndrome can be caused by mutations in the following gene/s location/s:
COL2A1 - 12q13.11
What are the main symptoms of Achondrogenesis, Type II; ACG2?
The typical symptoms of the syndrome are:
Narrow chest, Anteverted nares, Short nose, Micromelia, Micrognathia, Abnormality of bone mineral density, Abdominal distention, Long philtrum, Short long bone, Skeletal dysplasia, Frontal bossing, Umbilical hernia, Macrocephaly, Stillbirth, Broad long bones, Short thorax, Thickened nuchal skin fold, Short neck, Short tubular bones of the hand, Horizontal ribs, Autosomal dominant inheritance, Postaxial hand polydactyly, Cystic hygroma, Malar flattening, Disproportionate short-trunk short stature, Disproportionate short-limb short stature, Edema, Malformation of the heart and great vessels, Abnormality of the foot, Abnormality of the clavicle, Absent vertebral body mineralization, Aplasia/Hypoplasia of the lungs, Polyhydramnios, Cleft palate, Barrel-shaped chest, Hydrops fetalis, Short ribs, Hypoplastic iliac wing, Short stature
How does someone get tested for Achondrogenesis, Type II; ACG2?
The initial testing for Achondrogenesis, Type II; ACG2 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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