megalocornea

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.

Pedigree: 
Autosomal recessive
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

Aphakia, Congenital Primary

Clinical Characteristics
Ocular Features: 

There is complete absence of the lens and with it aplasia of the anterior segment including complete absence of the iris, ciliary body, and trabecular meshwork.  In an autopsied case, the cornea was thinned and lacked endothelium, Bowman layer, and Descemet membrane while the retina was dysplastic.  In the single family reported, 2 sibs had sclerocornea and one had megalocornea.  Normal pressure was reported in several eyes but a single eye in one patient at the age of 3 years developed buphthalmos with elevated pressure.

Systemic Features: 

No systemic abnormalities have been reported.

Genetics

Homozygosity of a nonsense mutation in the FOXE3 transcription factor gene (1p32) seems to be responsible for this autosomal recessive disorder.  The same gene has been implicated in rare cases of Peters anomaly (604229) and in anterior segment mesenchymal dysgenesis (107250).

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment is known to restore vision.

References
Article Title: 

Iridogoniodysgenesis and Skeletal Anomalies

Clinical Characteristics
Ocular Features: 

Megalocornea, congenital glaucoma, a concave iris with stromal atrophy and corectopia, and deep anterior chambers are typical ocular features.  High myopia has been reported and retinal detachments have been observed.  Glaucoma control can be difficult to achieve and there is a significant risk of cataracts and phthisis bulbi following surgery.  Posterior embryotoxon has not been observed.

Systemic Features: 

Facial features seem to be consistent.  The forehead is wide, the nose appears broad with a large nasal tip and broad nares although the bridge appears narrow.  The philtrum is long and wide.  The ears may appear large and the neck is short.  The thorax is abnormally wide and the nipples are widely spaced and umbilicated.  The long bones are slender with thin cortices and wide metaphyses.  There is generalized osteopenia.  Vertebral bodies are cuboid-shaped with narrow vertebral canals and enlarged apophyses

Genetics

Two non-consanguineous families each with 3 sibs have been reported suggesting autosomal recessive inheritance.  Nothing is known about the mutation or its locus.

The ocular features may resemble Rieger or Axenfeld anomaly but these are inherited in autosomal dominant patterns and the skeletal features are dissimilar.       

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Vigorous treatment of glaucoma is indicated but successful control, even with surgery, is difficult to achieve.

References
Article Title: 

Glaucoma, Congenital Primary D

Clinical Characteristics
Ocular Features: 

Evidence of glaucoma can appear in early childhood but may appear much later.  However, typical signs such as enlarged corneas or frank buphthalmos, cloudiness of the corneas, tearing and photophobia are present only when the pressure is elevated due to pupillary block or when the lens migrates into the anterior chamber.  Most patients have additional signs such as ectopia lentis and spherophakia.

Systemic Features: 

Some patients have osteopenia, a high arched palate, and a marfanoid habitus.

Genetics

This form of congenital glaucoma has been described primarily in Middle Eastern and Asian as well as Roma/Gypsy families and is inherited in an autosomal recessive pattern.  The mutations occur in the LTBP2 gene (14q24) which is in close proximity to GLC3C, another putative gene with mutations causing congenital glaucoma. 

Mutations in other genes are also associated with primary congenital glaucoma such as in CYP1B1 causing type A (231300) and in GLC3B causing type B (600975).

THIS IS NOT A PRIMARY GLAUCOMA DISORDER.  Microspherophakia and ectopia lentis are not features of primary congenital glaucoma.  Elevated pressures in these patients are found only when there is a pupillary block or when the lens dislocates into the anterior chamber.  The enlarged cornea is clear and has no breaks in the Descemet membrane.  THIS CONDITION IS THEREFORE RECLASSIFIED AS "MEGALOCORNEA, ECTOPIA LENTIS, AND SPHEROPHAKIA".     

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

The usual surgical and pharmacological treatments for glaucoma apply but vision preservation is a challenge.  The spherophakic or dislocated lenses may need to be removed.

References
Article Title: 

LTBP2 and CYP1B1 mutations and associated ocular phenotypes in the Roma/Gypsy founder population

Azmanov DN, Dimitrova S, Florez L, Cherninkova S, Draganov D, Morar B, Saat R, Juan M, Arostegui JI, Ganguly S, Soodyall H, Chakrabarti S, Padh H, L??pez-Nevot MA, Chernodrinska V, Anguelov B, Majumder P, Angelova L, Kaneva R, Mackey DA, Tournev I, Kalaydjieva L. LTBP2 and CYP1B1 mutations and associated ocular phenotypes in the Roma/Gypsy founder population. Eur J Hum Genet. 2011 Mar;19(3):326-33.

PubMed ID: 
21081970

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

Ectopia Lentis et Pupillae

Clinical Characteristics
Ocular Features: 

This disorder is generally considered to consist of simple displacement of the pupil and dislocation of the lens (usually in opposite directions).  However, other abnormalities are often present such as persistent pupillary membrane (87%), iridohyaloid adhesions, increased corneal thickness, enlarged corneal diameters, and axial myopia.  The iris may transilluminate (67%) and the pupils dilate poorly.  Iridodenesis is common (85%).  The lens is often malformed and in some cases frankly microspherophakic.  The lens displacement can progress and cataracts seem to form at a relatively young age.  Visual acuity is highly variable, ranging from 20/20 to light perception depending upon the density of cataracts which often develop at a relatively young age. Prominent iris processes into the anterior chamber angle have been reported and glaucoma, both acute and chronic, is sometimes seen.  Retinal detachment is a risk.

Studies in families with ectopia lentis et papillae have revealed that as many as 50% of individuals with dislocated lenses do not have ectopic pupils.

Systemic Features: 

None reported

Genetics

This disorder is usually inherited in an autosomal recessive pattern.  Multiple affected sibs have been born to consanquineous matings.  However, other families in which detailed ophthalmological examinations were done have suggested dominant inheritance based upon the presence of more subtle ocular signs in relatives.  This is likely a more clinically heterogeneous disorder than has been appreciated.

In five Norwegian families a homozygous 20 bp deletion has been found in the gene ADAMTSL4 on chromosome 1 (c.767_786del20) (1q21.3) producing a frameshift and the introduction of a stop codon leading to truncation of the protein product.  Mutations in the same gene have also been found in the autosomal recessive form of isolated ectopia lentis (225100).

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Glaucoma, retinal detachments, and cataracts may require surgery.

References
Article Title: 

Neuhauser Syndrome

Clinical Characteristics
Ocular Features: 

This rare disorder is characterized by profound mental retardation and megalocornea together with nonspecific facial features including epicanthal folds, broad nasal root, frontal bossing and antimongoloid lid slanting.

Systemic Features: 

Hypotonia and marked psychomotor retardation are the most prominent systemic features.   Short stature, hypercholesterolemia, seizures and hypothyroidism have also been reported.

Genetics

No specific mutation has been found.  Most cases occur sporadically.  The mode of inheritance is presumed to be autosomal recessive on the basis of parental consanquinity found in occasional parents with multiple affected offspring.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment is available.
 

References
Article Title: 

Association of CHRDL1 Mutations and Variants with X-linked Megalocornea, Neuhäuser Syndrome and Central Corneal Thickness

Davidson AE, Cheong SS, Hysi PG, Venturini C, Plagnol V, Ruddle JB, Ali H, Carnt N, Gardner JC, Hassan H, Gade E, Kearns L, Jelsig AM, Restori M, Webb TR, Laws D, Cosgrove M, Hertz JM, Russell-Eggitt I, Pilz DT, Hammond CJ, Tuft SJ, Hardcastle AJ. Association of CHRDL1 Mutations and Variants with X-linked Megalocornea, Neuhauser Syndrome and Central Corneal Thickness. PLoS One. 2014 Aug 5.

PubMed ID: 
25093588

PNPLA6 mutations cause Boucher-Neuhauser and Gordon Holmes syndromes as part of a broad neurodegenerative spectrum

Synofzik M, Gonzalez MA, Lourenco CM, Coutelier M, Haack TB, Rebelo A, Hannequin D, Strom TM, Prokisch H, Kernstock C, Durr A, Schols L, Lima-Martinez MM, Farooq A, Schule R, Stevanin G, Marques W Jr, Zuchner S. PNPLA6 mutations cause Boucher-Neuhauser and Gordon Holmes syndromes as part of a broad neurodegenerative spectrum. Brain. 2013 Dec 19. [Epub ahead of print].

PubMed ID: 
24355708
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