Haab striae

Glaucoma, Congenital Primary E

Clinical Characteristics
Ocular Features: 

Glaucoma is usually present at birth but sometimes not detected for several months.  Intraocular pressures are generally greater than 21 mm Hg.  Increased optic nerve cupping greater than 40% was also used to make the diagnosis in many individuals.  Ten families have been reported and in half the disease was unilateral only.

Systemic Features: 

No consistent systemic features are present.

Genetics

Heterozygous mutations in the TEK (9p21.2) gene (600221) are responsible for this disorder.  The TEK receptor is a tyrosine kinase primarily expressed in endothelial cells in mice, rats and humans.  In Tek-knockout mice Schlemm's canal and the trabecular meshwork are hypoplastic and dysmorphic.

For additional mutations and congenital glaucoma conditions see Glaucoma, Congenital Primary A.

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Standard glaucoma therapies should be applied early and lifelong monitoring is necessary.

References
Article Title: 

Angiopoietin receptor TEK mutations underlie primary congenital glaucoma with variable expressivity

Souma T, Tompson SW, Thomson BR, Siggs OM, Kizhatil K, Yamaguchi S, Feng L, Limviphuvadh V, Whisenhunt KN, Maurer-Stroh S, Yanovitch TL, Kalaydjieva L, Azmanov DN, Finzi S, Mauri L, Javadiyan S, Souzeau E, Zhou T, Hewitt AW, Kloss B, Burdon KP, Mackey DA, Allen KF, Ruddle JB, Lim SH, Rozen S, Tran-Viet KN, Liu X, John S, Wiggs JL, Pasutto F, Craig JE, Jin J, Quaggin SE, Young TL. Angiopoietin receptor TEK mutations underlie primary congenital glaucoma with variable expressivity. J Clin Invest. 2016 Jul 1;126(7):2575-87.

PubMed ID: 
27270174

Glaucoma, Congenital Primary B

Clinical Characteristics
Ocular Features: 

Type B congenital glaucoma is considerably more rare than type A and may be more common in Middle Eastern families.  Few families have been reported but the clinical features are similar: elevated intraocular pressure in infancy or early childhood, photophobia, and cloudy corneas (see Glaucoma, Congenital Primary A [231300] for a more complete description of the phenotype).

Systemic Features: 

No systemic abnormalities are associated.

Genetics

This is an autosomal recessive disorder caused by a mutation in GLC3B mapped to a locus at 1p36.2-p36.1.  Type A congenital glaucoma (231300) is caused by a mutation in CYP1B1 and type D by mutations in LTBP2 (613086).  A locus at 14q24.3 has been asssociated with another form of congenital glaucoma (613085; type C) but the nature of the gene is unknown.  Mutations in TEK are responsible for congenital glaucoma type GLC3E.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

As in other types of congenital glaucoma, pressure control is difficult and the best approach entails some form of glaucoma surgical filtration.

References
Article Title: 

Glaucoma, Congenital Primary A

Clinical Characteristics
Ocular Features: 

This may be the most common type of early (infantile, congenital) glaucoma.  Elevated intraocular pressure may be present at birth but sometimes is not evident until the first year of life or in some cases even later.  Irritability, photophobia, and epiphora are early signs.  The globe is often buphthalmic, the cornea is variably cloudy, and breaks in the Descemet membrane (Haab striae) may be present.  Frequently the iris root is inserted anteriorly in the region of the trabecular meshwork.  The anterior chamber often appears abnormally deep.  Early reports of a membrane covering the angle structures have not been confirmed histologically.  The mechanism causing elevated IOP seems to be excessive collagen tissue in the anterior chamber angle that impedes normal aqueous outflow.   The pressure is usually in the range of 25-35 mmHg but this is variable as the course can be intermittent.  It should be considered a bilateral disease although about one-fourth of patients have only unilateral elevations of pressure even though trabecular abnormalities are present.

Optic cupping may begin temporally but the more typical glaucomatous cupping eventually occurs.

Systemic Features: 

No consistent systemic abnormalities are associated with primary congenital glaucoma.  However, it is important to note that glaucoma is a feature of many congenital malformation syndromes and chromosomal aberrations.

Genetics

Congenital glaucoma of this type can result from both homozygous (25%) and compound heterozygous mutations (56%) in the CYP1B1 gene on chromosome 2 (2p22-p21) which codes for cytochrome P4501B1.

Evidence from many sources suggests that congenital glaucoma of this type is an autosomal recessive disorder. Parental consanguinity is common, the segregation ratio is approximately 25%, and the occurrence of congenital glaucoma among all offspring of two affected parents can be cited as support for this mode of inheritance.  Many cases occur sporadically but this is consistent with expectations in small human sibships.  Curiously, though, males are affected more often than females.

Another autosomal recessive infantile (congenital) glaucoma (600975), GLC3 or type B, is caused by mutations in GLC3B located at 1p36.2-p36.1.  A third locus at 14q24.3 has also been proposed  for GLC3, type C.  Autosomal recessive primary congenital glaucoma (so-called) type D (613086) is caused by a mutation in LTBP2 located at 14q24 near the GLC3C locus and heterozygous mutations in TEK are responsible for type E (617272).

Other modes of inheritance have been described and, for now, this form of glaucoma, like others, has to be considered a genetically and clinically heterogeneous disorder pending additional genotyping.  Early onset glaucoma is also a feature of numerous malformation and chromosomal disorders.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Some of the usual glaucoma drugs are ineffective as a result of obstruction to aqueous flow through the trabecular meshwork so that surgical treatment is the therapy of choice in most cases.   Monitoring of axial length has been proposed as helpful in gauging the effectiveness of pressure control.  In some patients the pressure normalizes spontaneously. 

It is important in the evaluation of patients with glaucoma that systemic evaluations be done because of the frequent syndromal associations.

References
Article Title: 

Congenital glaucoma and CYP1B1: an old story revisited

Alsaif HS, Khan AO, Patel N, Alkuraya H, Hashem M, Abdulwahab F, Ibrahim N, Aldahmesh MA, Alkuraya FS. Congenital glaucoma and CYP1B1: an old story revisited. Hum Genet. 2018 Mar 19. doi: 10.1007/s00439-018-1878-z.

PubMed ID: 
29556725
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