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The eye
Published in Angus Clarke, Alex Murray, Julian Sampson, Harper's Practical Genetic Counselling, 2019
Both bilateral coloboma of the iris and the more severe aniridia usually follow autosomal dominant inheritance; colobomas may form part of more extensive ocular disorders. Because colobomas may vary considerably in extent, a thorough ophthalmic examination of both the parents and the patient is needed. The rare syndrome of ocular coloboma with anal atresia (cat eye syndrome) follows an autosomal dominant pattern but is associated with an extra chromosome 22 fragment. Mutation in the gene CHD7 is an important cause of coloboma when it is a part of the condition CHARGE (coloboma, heart defects, atresia choanae, growth retardation, genital abnormalities and ear abnormalities) syndrome.
Clinical Cytogenetics and Testing for Developmental Disabilities
Published in Merlin G. Butler, F. John Meaney, Genetics of Developmental Disabilities, 2019
Joan H. M. Knoll, Linda D. Cooley
The most common non-Robertsonian translocation is the reciprocal translocation found in the general population involving chromosomes 11 and 22 and designatedas t(ll;22) (q23;q11.2). The shared sequence homology in the regions that exchange in this translocation is likely to account for its frequency (26-28). Carriers of this translocation are at risk of having chromosomally unbalanced children who have an additional small chromosome derived from chromosome 22. Children with this chromosomal imbalance have findings that overlap with the findings of children that have the cat-eye syndrome and who are tetrasomic (four copies) for part of chromosome 22q. This additional chromosome originates in the carrier parent due to aberrant chromosomal segregation during gametogenesis.
Individual conditions grouped according to the international nosology and classification of genetic skeletal disorders*
Published in Christine M Hall, Amaka C Offiah, Francesca Forzano, Mario Lituania, Michelle Fink, Deborah Krakow, Fetal and Perinatal Skeletal Dysplasias, 2012
Christine M Hall, Amaka C Offiah, Francesca Forzano, Mario Lituania, Michelle Fink, Deborah Krakow
Ocular coloboma: Renal coloboma syndrome (papillorenal syndrome) also presents with renal abnormalities and occasional hearing loss, but no other malformations; it is caused by mutations in the gene PAX2. Cat-eye syndrome is caused by a chromosomal anomaly (supernumerary invdup(22)(q11)) and is typically characterised by the association of colobomas, rectal atresia with fistula, urogenital and cardiac malformations and preauricular tags or pits. Joubert syndrome presents with cerebellar vermis aplasia/ hypoplasia and the typical ‘molar tooth sign’ on neuroimaging; also has polydactyly and fibrosis of the kidney and liver. Coloboma associated with growth retardation and cardiac anomalies can sometimes be found in Kabuki syndrome, which shows very distinctive facial features.
Mosaic cat eye syndrome in a child with unilateral iris coloboma
Published in Ophthalmic Genetics, 2021
Cristina Hernández-Medrano, Alberto Hidalgo-Bravo, Cristina Villanueva-Mendoza, Teresa Bautista-Tirado, David Apam-Garduño
Cat eye syndrome is a chromosomal disorder with a classic triad of iris coloboma, anorectal malformations, and auricular abnormalities. CES is caused by the presence of additional genetic material derived from chromosome 22. It may be present as a partial tetrasomy or trisomy, or simultaneous duplication and inversion of chromosome 22. This anomaly usually appears sporadically and may occur during gametogenesis, mainly in oogenesis, or as an early post-zygotic event (8). The proximal portion of the long arm of chromosome 22 (22q11.2) is a critical region for chromosomal rearrangements due to its high content of low copy repeats (LCRs). LCRs are chromosome regions where recombination events can occur between homologous chromosomes during meiosis. The mechanism leading to rearrangements is unclear, but the model of the U-type interchromosomal exchange has been postulated (8), where homologous chromosomes are misaligned due to the high LCR content. This misalignment and genomic crosslinking lead to segregation errors and non-allelic homologous recombination during cell division (1,2,8).
Atypical presentation of Cat Eye Syndrome in an infant with Peters anomaly and microphthalmia with cyst
Published in Ophthalmic Genetics, 2020
Benjamin Katz, Jennifer Enright, Steven Couch, George Harocopos, Andrew R. Lee
Cat Eye Syndrome (CES) is a rare chromosomal abnormality that results from a supernumerary dicentric bisatellited marker chromosome that causes a tetrasomy of the 22pter-22q11.2 region of chromosome 22 (1). CES has a broad range of phenotypes and is frequently characterized by the presence of iris colobomas, anal atresia, and ear anomalies (2). We present the case of a female infant with atypical ocular findings for CES exhibiting unilateral Peters anomaly and contralateral microphthalmia with cyst, without the classic finding of iris coloboma.