corneal pannus

Hereditary Mucoepithelial Dysplasia

Clinical Characteristics

Ocular Features

Impaired epithelial cohesion, including that of the cornea, is the fundamental defect in this disorder.  Photophobia may be present in infants and this is soon evident as secondary to keratitis with eventual formation of a pannus and corneal neovascularization.  Vision is impaired early and as the disease progresses, many patients by early adulthood are severely impaired.  Cataracts are present in the majority of individuals, often present as early as the second decade of life.  Eyelashes and eyebrows may be sparse.  Nystagmus has been reported in some patients.

Systemic Features

This is a panepithelial disease of impaired cohesion due, at least in part, to a reduced number of desmosomes and defective gap junctions.  Oral, nasal, vaginal, cervical, perineal, urethral, and bladder mucosa, in addition to external ocular surfaces, are involved.  With exception of the ocular involvement, the lesions are usually not painful, but may be during acute flare-ups.  Demarcated erythematous patches are often seen in the oral mucosa.  Non-scarring alopecia, keratosis pilaris, and perineal intertrigo are usually present.  Histological examination of oral mucosa and skin shows dyskeratotic features, decreased number of desmosomes, and intracytoplasmic vacuoles.

Genetics

Pedigrees suggest autosomal dominant inheritance but few families have been reported.  The location of the responsible mutation, if any, has not been found. 

Somewhat similar genodermatoses are KID syndrome (148210), an autosomal dominant disorder with neurosensory hearing loss and sometimes mental and physical delays secondary to mutations in GJB2, and IFAP (308205), an X-linked condition with mental and physical delays and severe organ deformities.  Cataracts are not features of KID or IFAP syndromes.

Treatment Options

No effective treatment has been found.

References

Boralevi F, Haftek M, Vabres P, Lepreux S, Goizet C, Leaute-Labreze C, Taieb A. Hereditary mucoepithelial dysplasia: clinical, ultrastructural and genetic study of eight patients and literature review. Br J Dermatol. 2005 Aug;153(2):310-8. Review.

PubMed ID: 
16086741

Witkop CJ Jr, White JG, Waring GO. Hereditary mucoepithelial dysplasia, a disease of gap junction and desmosome formation. Birth Defects Orig Artic Ser. 1982;18(6):493-511.

PubMed ID: 
7171771

Foveal Hypoplasia

Clinical Characteristics

Ocular Features

This is a poorly defined syndrome with features overlapping aniridia, hereditary keratitis, ocular albinism, and iris anomalies as in Peters anomaly.  However, presenile cataracts seem to be unique to this disorder.  The foveal hypoplasia may occur without other anomalies although the fundus is usually lightly pigmented.  As expected, acuity is subnormal from birth, in the range of 20/50, and dyschromatopsia may be present.  Some patients have nystagmus.  Weak iris transillumination has been reported and a small limbal pannus may be present. Lens opacities may become visually significant in the third to fourth decade of life.  OCT has shown abnormal foveal thickness with multiple inner retinal layers somewhat similar to the situation in oculocutaneous albinism (203100) and it has been suggested that 'foveal dysplasia' is a better description than 'foveal hypoplasia'. 

Systemic Features

No systemic disease is present. 

Genetics

This disorder is associated with mutations in the PAX6 gene (11p13) and inherited as an autosomal dominant.

The protein product of the PAX6 gene is a transcription factor that attaches to DNA and regulates the expression of other genes.  PAX6 plays a major role primarily in development of the eye and central nervous system but evidence suggests it is also active postnatally.  Hundreds of mutations have been found in disorders such as hereditary keratitis, aniridia, Peters anomaly, hypoplasia and colobomas of the optic nerve.  This database contains 8 conditions in which mutations in PAX6 seem to be responsible, including syndromal conditions such as Str√∏mme and Gillespie syndromes in which there may be cognitive disabilities. 

True isolated foveal hypoplasia without lens or corneal disease does exist as well but this condition is not well defined.  Homozygous mutations in SLC38A8 have been found to cosegregate with foveal hypoplasia among families of Jewish Indian ancestry.  Hypopigmentation is not a feature of isolated foveal hypoplasia secondary to such mutations but misrouting of optic nerve axons may be present.  Nystagmus and reduced vision but no anterior segment abnormalities were present.

With the widespread utilization of OCT measurements, we have learned that underdevelopment of the fovea can be a feature of numerous ocular disorders (more than 20 in this database).  In most conditions, the foveal dysplasia is part of a disease complex as in foveal hypoplasia with anterior segment dysgenesis (609218).

 

Treatment Options

Cataract surgery is indicated when lens opacities become visually significant. 

References

Poulter JA, Al-Araimi M, Conte I, van Genderen MM, Sheridan E, Carr IM, Parry DA, Shires M, Carrella S, Bradbury J, Khan K, Lakeman P, Sergouniotis PI, Webster AR, Moore AT, Pal B, Mohamed MD, Venkataramana A, Ramprasad V, Shetty R, Saktivel M, Kumaramanickavel G, Tan A, Mackey DA, Hewitt AW, Banfi S, Ali M, Inglehearn CF, Toomes C. Recessive Mutations in SLC38A8 Cause Foveal Hypoplasia and Optic Nerve Misrouting without Albinism. Am J Hum Genet. 2013 Dec 5;93(6):1143-50. doi: 10.1016/j.ajhg.2013.11.002. Epub 2013 Nov 27. PubMed PMID: 24290379;

PubMed ID: 
24290379

Perez Y, Gradstein L, Flusser H, Markus B, Cohen I, Langer Y, Marcus M, Lifshitz T, Kadir R, Birk OS. Isolated foveal hypoplasia with secondary nystagmus and low vision is associated with a homozygous SLC38A8 mutation. Eur J Hum Genet. 2013 Sep 18.  [Epub ahead of print].

PubMed ID: 
24045842

Thomas S, Thomas MG, Andrews C, Chan WM, Proudlock FA, McLean RJ, Pradeep A, Engle EC, Gottlob I. Autosomal-dominant nystagmus, foveal hypoplasia and presenile cataract associated with a novel PAX6 mutation. Eur J Hum Genet. 2013 Aug 14. [Epub ahead of print].

PubMed ID: 
23942204

Saffra N, Agarwal S, Chiang JP, Masini R, Bertolucci A. Spectral-domain optical coherence tomographic characteristics of autosomal recessive isolated foveal hypoplasia. Arch Ophthalmol. 2012 Oct 1;130(10):1324-7.  PubMed PMID: 23044950.

PubMed ID: 
23044950

Recchia FM, Carvalho-Recchia CA, Trese MT. Optical coherence tomography in the diagnosis of foveal hypoplasia. Arch Ophthalmol. 2002 Nov;120(11):1587-8.

PubMed ID: 
12427081

Azuma N, Nishina S, Yanagisawa H, Okuyama T, Yamada M. PAX6 missense mutation in isolated foveal hypoplasia. Nat Genet. 1996 Jun;13(2):141-2.

PubMed ID: 
8640214

O'Donnell FE Jr, Pappas HR. Autosomal dominant foveal hypoplasia and presenile cataracts. A new syndrome. Arch Ophthalmol. 1982 Feb;100(2):279-81.

PubMed ID: 
7065945

Aniridia

Clinical Characteristics

Ocular Features

Aniridia is both the name of a disease and a group of disorders.  This because aniridia is both an isolated ocular disease and a feature of several malformation syndromes.  Absence of the iris was first reported in the early 19th century.  The hallmark of the disease is bilateral iris hypoplasia which may consist of minimal loss of iris tissue with simple radial clefts, colobomas, pseudopolycoria, and correctopia, to nearly complete absence.  Goniosocopy may be required to visualize tags of iris root when no iris is visible externally.  Glaucoma is frequently present (~67%) and often difficult to treat.  It is responsible for blindness in a significant number of patients.  About 15% of patients are diagnosed with glaucoma in each decade of life but this rises to 35% among individuals 40-49 years of age.  Hypoplasia and dysplasia of the fovea are likely responsible for the poor vision in many individuals.  Nystagmus is frequently present.  The ciliary body may also be hypoplastic. 

Visual acuity varies widely.  In many families it is less than 20/60 in all members and the majority have less than 20/200.  Photophobia can be incapacitating.  Posterior segment OCT changes suggest that outer retinal damage suggestive of a phototoxic retinopathy may also be a factor in the reduced acuity.  Cataracts (congenital in >75%), ectopia lentis (bilateral in >26%), optic nerve hypoplasia, variable degrees of corneal clouding with or without a vascularized pannus, and dysgenesis of the anterior chamber angle are frequently present. 

Increased corneal thickness (>600 microns) has been found in some series and should be considered when IOP measurements are made.  In early stages of the disease, focal opacities are present in the basal epithelium, associated with sub-basal nerves.  Dendritic cells can infiltrate the central epithelium and normal limbal palisade architecture is absent.  The tear film is often unstable.

Attempts have been made to divide aniridia into several types based upon the type and degree of ocular abnormalities but modern genotyping allows more specific determination of classification, especially when systemic features are also considered.

Systemic Features

In addition to ‘pure’ aniridia in which no systemic features are found, at least six disorders have been reported in which systemic anomalies do occur.  Three of these have associated renal anomalies, including Wilms tumor with other genitourinary anomalies and mental retardation, sometimes called WAGR (194072) syndrome, another (612469) with similar features plus obesity sometime called WAGRO (612469) syndrome reported in isolated patients, and yet another with partial aniridia (206750) and unilateral renal agenesis and psychomotor retardation reported in a single family.  Aniridia with dysplastic or absent patella (106220) has been reported in a single three generation family.  Cerebellar ataxia and mental retardation with motor deficits (Gillespie syndrome; 206700) has been found in other families.  Another 3 generation family has been reported in which aniridia, microcornea and spontaneously resorbed cataracts occured (106230).

About one-third of patients with aniridia also have Wilms tumor and many have some cognitive deficits..

Genetics

The majority of cases have a mutation in the paired box gene (PAX6) complex, or at least include this locus when chromosomal aberrations such as deletions are present in the region (11p13).  This complex (containing at least 9 genes) is multifunctional and important to the tissue regulation of numerous developmental genes.   PAX6 mutations, encoding a highly conserved transcription regulator, generally cause hypoplasia of the iris and foveal hypoplasia but are also important in CNS development.  It has been suggested that the PAX6 gene may be the only gene defect associated with aniridia.  More than 300 specific mutations, most causing premature truncation of the polypeptide, have been identified.  Associated abnormalities may be due to a second mutation in the WT1 gene in WAGR (194072) syndrome, a deletion syndrome involving both WT1 and PAX6 genes at 11p13.  The WAGRO syndrome (612469) is caused by a contiguous deletion in chromosome 11 (11p12-p13) involving three genes: WT1, PAX6, and BDNF.  All types are likely inherited as autosomal dominant disorders although nearly one-third of cases occur sporadically.

Mutations in PAX6 associated with aniridia can cause other anterior chamber malformations such as Peters anomaly (604229).

Gillespie syndrome (206700 ) is an allelic disorder with neurological abnormalities.

Treatment Options

Treatment is directed at the associated threats to vision such as glaucoma, corneal opacities, and cataracts.  Glaucoma is the most serious threat to vision and difficult to treat although good results have been reported with glaucoma drainage devices.  All patients should have eye examinations at appropriate intervals throughout life, focused on glaucoma screening.  It is well to keep in mind that foveal maldevelopment often precludes significant improvement in acuity and heroic measures must be carefully evaluated.  Specifically, corneal transplants frequently fail.

Low vision aids are often helpful.  Tinted lenses can minimize photophobia.  Occupational and vocational training should be considered for older individuals.

Young children with aniridia should have periodic examinations with renal imaging as recommended by a urologist.

In mice, postnatal topical ocular application of ataluren-based eyedrop formulations can reverse malformations caused by PAX6 mutations.

References

Gregory-Evans CY, Wang X, Wasan KM, Zhao J, Metcalfe AL, Gregory-Evans K. Postnatal manipulation of Pax6 dosage reverses congenital tissue malformation defects. J Clin Invest. 2014 Jan 2;124. Epub 2013 Dec 20.

PubMed ID: 
24355924

Edén U, Fagerholm P, Danyali R, Lagali N. Pathologic Epithelial and Anterior Corneal Nerve Morphology in Early-Stage Congenital Aniridic Keratopathy. Ophthalmology. 2012 Apr 17. [Epub ahead of print].

PubMed ID: 
22512983

Gramer E, Reiter C, Gramer G. Glaucoma and frequency of ocular and general diseases in 30 patients with aniridia: a clinical study. Eur J Ophthalmol. 2012 Jan;22(1):104-10. doi: 10.5301/EJO.2011.8318.

PubMed ID: 
22167549

Gregory-Evans K, Cheong-Leen R, George SM, Xie J, Moosajee M, Colapinto P, Gregory-Evans CY. Non-invasive anterior segment and posterior segment optical coherence tomography and phenotypic characterization of aniridia. Can J Ophthalmol. 2011 Aug;46(4):337-44. Epub 2011 Jul 7.

PubMed ID: 
21816254

Sawada M, Sato M, Hikoya A, Wang C, Minoshima S, Azuma N, Hotta Y. A case of aniridia with unilateral Peters anomaly. J AAPOS. 2011 Feb;15(1):104-6.

PubMed ID: 
213997818

Kokotas H, Petersen MB. Clinical and molecular aspects of aniridia. Clin Genet. 2010 May;77(5):409-20.

PubMed ID: 
20132240

Robinson DO, Howarth RJ, Williamson KA, van Heyningen V, Beal SJ, Crolla JA. Genetic analysis of chromosome 11p13 and the PAX6 gene in a series of 125 cases referred with aniridia. Am J Med Genet A. 2008 Mar 1;146A(5):558-69.

PubMed ID: 
18241071

Elsas FJ, Maumenee IH, Kenyon KR, Yoder F. Familial aniridia with preserved ocular function. Am J Ophthalmol. 1977 May;83(5):718-24.

PubMed ID: 
868970