Megalocornea, Ectopia Lentis, and Spherophakia

Clinical Characteristics
Ocular Features: 

Patients have megalocornea and mobile lenses.  Corneal diameters are at least 13 mm in diameter.  Some lenses are spherophakic (refractive errors may be in the +11-12 diopter range) and sometimes displace into the anterior chamber or cause pupillary block glaucoma.  The clinical picture often resembles congenital glaucoma in young children but the elevated pressure is usually secondary to hypermobility of the lens and/or its spherical shape.  Haab striae are not present but cloudy corneas have been reported in a few patients.

Many patients develop phthisis or have severe reductions in vision.

Systemic Features: 

Some but not all patients have several physical features of the Marfan syndrome (154700) such as high arched palate, tall stature, and narrow face but those tested do not have mutations in the FBN1 gene.

Genetics

This is an autosomal recessive disorder.  Parental consanguinity is common.  Homozygous mutations in the LTBP2 gene (14q24.3) are found in affected individuals.

LTBP2 competes with LTBP1 (ADAMTSL2) for binding to the gene product of FBN1 in which mutations are associated with the Marfan syndrome (154700) and may account for the variable skeletal signs sometimes found in patients with this megalocornea syndrome.  Both gene products are important to the structure of the extracellular matrix proteins of the ciliary processes, lens capsule, and lens epithelial layer.  The different modes of inheritance and the unique mutations, of course, argue for separateness of the two disorders.

Mutations in LTBP2 have also been found in a family with microspherophakia and ectopia lentis but corneal diameters were described as normal suggesting clinical heterogeneity.

This is a unique disorder which previously has been classified as Glaucoma, Congenital Primary D (613086).  The usual occurrence of ectopia lentis,  the sometimes spherophakic nature of the lenses, the congenital presence of megalocornea without corneal edema in the absence of elevated intraocular pressure, and the lack of breaks in the Descemet membrane strongly suggest that this is not a primary congenital glaucoma.

Treatment
Treatment Options: 

Urgent lensectomy is necessary for lenses that migrate into the anterior chamber.  Patients have to be monitored as lens dislocations can occur at any age.

References
Article Title: 

Null mutations in LTBP2 cause primary congenital glaucoma

Ali M, McKibbin M, Booth A, Parry DA, Jain P, Riazuddin SA, Hejtmancik JF, Khan SN, Firasat S, Shires M, Gilmour DF, Towns K, Murphy AL, Azmanov D, Tournev I, Cherninkova S, Jafri H, Raashid Y, Toomes C, Craig J, Mackey DA, Kalaydjieva L, Riazuddin S, Inglehearn CF. Null mutations in LTBP2 cause primary congenital glaucoma. Am J Hum Genet. 2009 May;84(5):664-71.

PubMed ID: 
19361779

References

Khan AO, Aldahmesh MA, Alkuraya FS. Congenital megalocornea with zonular weakness and childhood lens-related secondary glaucoma - a distinct phenotype caused by recessive LTBP2 mutations. Mol Vis. 2011;17:2570-9.

PubMedID: 22025892

D?(c)sir J, Sznajer Y, Depasse F, Roulez F, Schrooyen M, Meire F, Abramowicz M. LTBP2 null mutations in an autosomal recessive ocular syndrome with megalocornea,spherophakia, and secondary glaucoma. Eur J Hum Genet. 2010 Jul;18(7):761-7.

PubMedID: 20179738

Kumar A, Duvvari MR, Prabhakaran VC, Shetty JS, Murthy GJ, Blanton SH. A homozygous mutation in LTBP2 causes isolated microspherophakia. Hum Genet. 2010 Oct;128(4):365-71.

PubMedID: 20617341

Ali M, McKibbin M, Booth A, Parry DA, Jain P, Riazuddin SA, Hejtmancik JF, Khan SN, Firasat S, Shires M, Gilmour DF, Towns K, Murphy AL, Azmanov D, Tournev I, Cherninkova S, Jafri H, Raashid Y, Toomes C, Craig J, Mackey DA, Kalaydjieva L, Riazuddin S, Inglehearn CF. Null mutations in LTBP2 cause primary congenital glaucoma. Am J Hum Genet. 2009 May;84(5):664-71.

PubMedID: 19361779