Amelogenesis Imperfecta, Hypomaturation Type, IIA1; AI2A1

What is Amelogenesis Imperfecta, Hypomaturation Type, IIA1; AI2A1?

Amelogenesis Imperfecta, Hypomaturation Type, IIA1; AI2A1 is a rare disease. It is also known as AIH1 Amelogenesis Imperfecta, Pigmented Hypomaturation Type, 1.

This category refers mainly to the X-linked type of hypomaturation amelogenesis, but there are both dominant and recessive pedigrees (Creton and Cune, 2004) in the literature. In hemizygous males (X-linked type) all of the teeth are involved although the maxillary incisors are most severely affected. The teeth are discoloured (brown or yellow) and they occasionally have a semi-transparent appearance. The teeth of carrier females show characteristic vertical grooves and, using the scanning electron microscope, vertical bands of normal and hypomature enamel can be seen (Sauk et al., 1972). Lagerstrom et al., (1991) demonstrated a deletion in the amelogenin gene in an X-linked family. An expressed copy of the amelogenin gene (AMGY) is also present in the pericentric region of the Y-chromosome but splicing may be different from that in AMGX mRNA (Salido et al., 1992). X-linkage accounts for about 5% of AI cases.
Lagerstrom et al., (1990) mapped the gene to Xp22, however Aldred et al., (1992) found evidence for a second locus at Xq22-Xq28 in one family. Further clinical details of this family were given by Crawford and Aldred (1993). A female in one of the Aldred et al., (1992) families was re-reported by Lykogeorgos et al., (2004). She had unusual manifestations seen more commonly in autosomal AI. These were taurodontism, pulpal calcification, cronal defects prior to tooth eruption and unerupted teeth.
Angelos and Jorgenson (1993) reported a possible case of X-linked amelogenesis imperfecta where scanning EM of the hair showed small cuticular pits. Macroscopically the hair in the proband was described as "abundant curly ... somewhat difficult to manage".
Dominant families have also been reported mapping to 4q21 (MacDougall et al., 1997). Rajpar et al., (2001) studied autosomal dominant amelogenesis imperfecta and found a mutation in the enamel-specific protein, gene enamelin (ENAM). Mutations in enamelin in 2 families were reported by Kim et al., (2005). There are 2 types - smooth hypoplastic and local hypoplastic, the local type from haploinsufficiency and adominant negative effect in the severe type (Wright, 2006).
A recessive family reported by Hart et al., (2003) mapped to 4q - homozygous mutations in ENAM were detected. Autosomal recessive hypomaturation amelogenesis imperfecta has been mapped to 19q13, and mutations found in KLK 4 (Hart et al., 2004). This gene, of the kallikrein family, belongs to the serine protease superfamily. Abnormal kallikrein 4 activity causes the enamel crystallites to grow incompletely in thickness or width. Another family with recessive (a father and son were affected, but this was pseudo-dominance), pigmented hypomaturation type of amelogenesis, was reported by Kim et al., (2005). The son had teeth of normal size, with a pigmented enamel layer, but with brown discolouration. The enamel was fragile. Both father and son were homozygous for mutations in enamelysin (MMP-20). Enamelysin is one of the 2 proteinases (the other is kallikrein-4 or KLK4), secreted by ameloblasts. It maps to 11q22. Nine Pakistani families with recessive hypomaturation type were mapped to 15q21 and mutations were found in WDR72 (El-Sayed et al., 2009). Two Turkish siblings had WDR72 mutations (Kuechler et al., 2012).Mutations in C4orf26 also cause recessive AI (Parry et al., 2012)
A new AD locus in a Brazilian family at 8q24 is suggested by Mendoza et al., (2007). A Korean family (hypocalcified type) reported by Kim et al., (2008), mapped to the same region and mutations were found in FAM83H . A farther and daughter (Kantaputra et al., 2016) had FAM83H mutations.
Mutations in ITGB6 can cause autosomal recessive amylogenesis imperfecta (Wang et al., 2014). Mutations in AMBN (recessive) can also cause the condition (Poulter et al., 2014)

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* This information is courtesy of the L M D.

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What gene changes cause Amelogenesis Imperfecta, Hypomaturation Type, IIA1; AI2A1?

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.


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.


X-Linked Dominant - With syndromes inherited in an X-linked dominant pattern, a mutation in just one of the copies of the gene causes the syndrome. This can be in one of the female X chromosomes, and in the one X chromosome males have. Males tend to have more severe symptoms than females.


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 - 204700 (please check the OMIM page for updated information)

The syndrome can be caused by mutations in the following gene/s location/s:
N/A

What are the main symptoms of Amelogenesis Imperfecta, Hypomaturation Type, IIA1; AI2A1?

The typical symptoms of the syndrome are:
Amelogenesis imperfecta, Carious teeth, Autosomal recessive inheritance

How does someone get tested for Amelogenesis Imperfecta, Hypomaturation Type, IIA1; AI2A1?

The initial testing for Amelogenesis Imperfecta, Hypomaturation Type, IIA1; AI2A1 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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