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Disease Profile

Congenital microcoria

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.


US Estimated

Europe Estimated

Age of onset






Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.

Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

Microcoria, congenital; MCOR; Congenital miosis;


Congenital and Genetic Diseases; Eye diseases


Congenital microcoria is a rare eye disorder affecting the development of the irises. It is characterized by absence or incomplete development of the iris dilator muscles (also called the pupil dilator muscles), making the pupils unable to dilate (widen).[1] People with congenital microcoria have small pupils (with a diameter less than 2 millimeters) that dilate poorly or not at all, even when pupil-dilating medicines (eye drops) are put on the eye.[1][2] The disorder is also often associated with nearsightedness, and glaucoma in childhood or early adulthood.[1][3][4]

Congenital microcoria that is not associated with an underlying syndrome is caused by a small, missing piece of genetic material (deletion) around a region of chromosome 13 designated as 13q32.[1][2] This region contains several genes, although it appears the exact gene or genes in the region responsible for congenital microcoria are still under investigation.[1] Inheritance is autosomal dominant.[1][2][3] Congenital microcoria is also a feature of autosomal recessive Pierson syndrome, caused by mutations in the LAMB2 gene.[4]

Standard treatment guidelines for congenital microcoria have not been established, but glaucoma usually requires medicine or surgery to lower pressure within the eyes. Eye glasses or contacts may be used for nearsightedness.[4]


This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
5%-29% of people have these symptoms
1%-4% of people have these symptoms
Ocular hypertension
High eye pressure
Percent of people who have these symptoms is not available through HPO
Autosomal dominant inheritance
Hypoplasia of the iris dilator muscle
Constricted pupils
Pupillary constriction

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Close sighted
Near sighted
Near sightedness

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Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

Organizations Supporting this Disease

    Organizations Providing General Support

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      These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

      In-Depth Information

      • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
      • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
      • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
      • PubMed is a searchable database of medical literature and lists journal articles that discuss Congenital microcoria. Click on the link to view a sample search on this topic.


        • A diagram of the eye can be found by visiting MedlinePlus, the National Library of Medicine Web site designed to help you research your health questions. Click on MedlinePlus to view the diagram.


          1. Fares-Taie L, Gerber S, Tawara A, et al. Submicroscopic deletions at 13q32.1 cause congenital microcoria. Am J Hum Genet. April 2, 2015; 96(4):631-639. https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/25772937/.
          2. O'Neill MJF. MICROCORIA, CONGENITAL. OMIM. May 14, 2015; https://www.omim.org/entry/156600.
          3. Congenital microcoria. Orphanet. https://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=en&Expert=566. Accessed 2/20/2018.
          4. Microcoria, congenital. The University of Arizona Health Sciences Center. https://disorders.eyes.arizona.edu/disorders/microcoria-congenital. Accessed 2/20/2018.