Microcoria, Congenital

Clinical Characteristics
Ocular Features: 

This disorder is a type of anterior chamber dysgenesis since the pupil and iris anomalies are associated with goniodysgenesis (prominent iris processes and high iris root insertion) and glaucoma.  The dilator muscle of the iris is hypoplastic and even topical mydriatics have little impact on pupil size. The pupil has a mean diameter of 0.8 mm and only dilates to a mean size of 1.4 mm.  The iris stroma is also hypoplastic and often lacks crypts and collarettes.  Transillumination defects of the iris are consistently present.  Axial myopia is a feature in some families (83% of affected individuals have refractive errors in the range of -10D) and seems to be progressive .  Juvenile glaucoma is frequently present (at least 30% require treatment) and is usually detected in the second (20%) through fourth decades of life.  All patients with glaucoma have evidence of 'trabeculodysgenesis' but the same features may also be seen in some patients without glaucoma.  The intraocular pressure is difficult to control pharmacologically.  Visual acuity varies widely but no retinal changes have been described.

Ultrastructural studies show lack of myofilaments and desmin in the stromal cytoplasmic processes of the anterior pigmented cells of the iris suggesting failure of full development of the pupil dilator muscle cells.

Systemic Features: 

There are no systemic abnormalities in this condition.

Genetics

This is an autosomal dominant disorder secondary to a mutation located at 13q13-q32.  The specific mutation responsible has not been identified but a large deletion at 13q32.1 in one patient has been reported. 

Congenital microcoria is also a feature of autosomal recessive Pierson syndrome (609049) caused by homozygous mutations in the LAMB2 gene.

Treatment
Treatment Options: 

Glaucoma often requires surgery for control of intraocular pressure.

References
Article Title: 

Submicroscopic deletions at 13q32.1 cause congenital microcoria

Fares-Taie L, Gerber S, Tawara A, Ramirez-Miranda A, Douet JY, Verdin H, Guilloux A, Zenteno JC, Kondo H, Moisset H, Passet B, Yamamoto K, Iwai M, Tanaka T, Nakamura Y, Kimura W, Bole-Feysot C, Vilotte M, Odent S, Vilotte JL, Munnich A, Regnier A, Chassaing N, De Baere E, Raymond-Letron I, Kaplan J, Calvas P, Roche O, Rozet JM. Submicroscopic deletions at 13q32.1 cause congenital microcoria. Am J Hum Genet. 2015 Apr 2;96(4):631-9.

PubMed ID: 
25772937

References

Sergouniotis PI, Ellingford JM, O'Sullivan J, Fenerty CH, Black GC. Genome sequencing identifies a large deletion at 13q32.1 as the cause of microcoria and childhood-onset glaucoma. Acta Ophthalmol. 2016 Sep 28. doi: 10.1111/aos.13246. [Epub ahead of print].

PubMedID: 27678338

Fares-Taie L, Gerber S, Tawara A, Ramirez-Miranda A, Douet JY, Verdin H, Guilloux A, Zenteno JC, Kondo H, Moisset H, Passet B, Yamamoto K, Iwai M, Tanaka T, Nakamura Y, Kimura W, Bole-Feysot C, Vilotte M, Odent S, Vilotte JL, Munnich A, Regnier A, Chassaing N, De Baere E, Raymond-Letron I, Kaplan J, Calvas P, Roche O, Rozet JM. Submicroscopic deletions at 13q32.1 cause congenital microcoria. Am J Hum Genet. 2015 Apr 2;96(4):631-9.

PubMedID: 25772937

Ramprasad VL, Sripriya S, Ronnie G, Nancarrow D, Saxena S, Hemamalini A, Kumar D, Vijaya L, Kumaramanickavel G. Genetic homogeneity for inherited congenital microcoria loci in an Asian Indian pedigree. Mol Vis. 2005 Nov 3;11:934-40.

PubMedID: 16288197

Tawara A, Itou K, Kubota T, Harada Y, Tou N, Hirose N. Congenital microcoria associated with late-onset developmental glaucoma. J Glaucoma. 2005 Oct;14(5):409-13.

PubMedID: 16148591

Toulemont PJ, Urvoy M, Coscas G, Lecallonnec A, Cuvilliers AF. Association of congenital microcoria with myopia and glaucoma. A study of 23 patients with congenital microcoria. Ophthalmology. 1995 Feb;102(2):193-8.

PubMedID: 7862406

Simpson WA, Parsons MA. The ultrastructural pathological features of congenital microcoria. A case report. Arch Ophthalmol. 1989 Jan;107(1):99-102.

PubMedID: 2910294