iris anomalies

Alagille Syndrome

Clinical Characteristics
Ocular Features: 

The ocular findings in Alagille syndrome are often of little functional significance but can be sufficient to suggest the diagnosis without further study of the systemic features.  Posterior embryotoxon is found in 95% of individuals while iris abnormalities such as ectopic pupils are seen in 45%, abnormal fundus pigmentation is common (hypopigmentation in 57%, diffuse pigment speckling in 33%), and optic disc anomalies have been reported in 76%.  One study found that 90% of individuals have optic disk drusen by ultrasonography.  The anterior chamber anomalies are considered by some to be characteristic of Axenfeld anomaly.  The presence of these ocular findings in children with cholestasis should suggest Alagille syndrome.  Ocular examination of the parents can also be helpful in this autosomal dominant disorder as some of the same changes are present in one parent in more than a third of cases.

Systemic Features: 

A variety of  systemic features, some of them serious malformations, occur in Alagille syndrome.  Among the most common is a partial intrahepatic biliary atresia leading to cholestasis and jaundice.  Skeletal malformations include 'butterfly' vertebrae, shortened digits, short stature, a broad forehead, and a pointed chin.  The tip of the nose may appear bulbous.  These features have suggested to some that there is a characteristic facial dysmorphology.  Vascular malformations are common including aneurysms affecting major vessels, valvular insufficiency, coarctation of the aorta, and stenosis and these are often responsible for the most serious health problems.  In fact, vascular events have been reported to be responsible for mortality in 34% of one cohort.  Chronic renal insufficiency develops in a minority of patients.  This disorder should always be considered in children with cholestasis, especially when accompanied by cystic kidney disease.  Brain MRIs may show diffuse or focal hyperintensity of white matter even in the absence of hepatic encephalopathy.

Genetics

This is an autosomal dominant condition secondary to various mutations in the JAG1 gene located on chromosome 20 (20p12).  Penetrance is nearly 100% but there is considerable variation in expression.  A far less common variant of this disorder, ALGS2 (610205), is caused by a mutation in the NOTCH2 gene (1p13-p11).

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

No cure is available but individual organ disease may be treatable.  The ocular abnormalities generally do not cause vision difficulties.

Reversible of white matter changes has been noted in a single child following liver transplantation.

 

References
Article Title: 

CT-defined phenotype of pulmonary artery

Rodriguez RM, Feinstein JA, Chan FP. CT-defined phenotype of pulmonary artery
stenoses in Alagille syndrome. Pediatr Radiol. 2016 Apr 4. [Epub ahead of print].

PubMed ID: 
27041277

Alagille syndrome: clinical and ocular pathognomonic features

El-Koofy NM, El-Mahdy R, Fahmy ME, El-Hennawy A, Farag MY, El-Karaksy HM. Alagille syndrome: clinical and ocular pathognomonic features. Eur J Ophthalmol. 2010 Jul 28. pii: 192165A5-8631-4C06-9C47-9AD63688B02A. [Epub ahead of print]

PubMed ID: 
20677167

Ocular abnormalities in Alagille syndrome

Hingorani M, Nischal KK, Davies A, Bentley C, Vivian A, Baker AJ, Mieli-Vergani G, Bird AC, Aclimandos WA. Ocular abnormalities in Alagille syndrome. Ophthalmology. 1999 Feb;106(2):330-7.

PubMed ID: 
9951486

Megalocornea

Clinical Characteristics
Ocular Features: 

The corneal diameter is enlarged at birth to between 13.0 and 16.5 mm and the anterior chamber is deep.  Male patients may develop early arcus, and eventually a crocodile shagreen pattern in the cornea.  Presenile cataracts, iris thinning, and iridodenesis have also been reported.  Glaucoma does not seem to be a part of this syndrome.  The ERG has revealed mild cone system dysfunction in some patients.. 

Systemic Features: 

Isolated megalocornea is not associated with systemic disease by definition but systemic evaluation must be performed to rule out other syndromes.

Some patients have been reported to have a focal loss of white matter myelination with superior cognitive abilities.

Genetics

Only a few pedigrees have been reported.  X-linked (male only) inheritance is most common.  Carrier females do not have ocular disease.  Multiple mutations in CHRDL1 (Xq23) have been found in at least 7 families. The gene encodes ventroptin, a morphogenic protein antagonist with multiple functions including specification of topographic retinotectal projections..  The gene is expressed in corneal development, anterior segment, and retina as well as brain.

Notably, megalocornea not only occurs as an isolated trait but also may be a part of systemic syndromes such as the Marfan syndrome (154700), Down syndrome andRieger syndrome (180500 ).  It is also a part of an autosomal recessive mental retardation syndrome, sometimes called Neuhauser syndrome (249310).

Autosomal inheritance (usually recessive) has also been suggested but no locus has been found on autosomes.

Homozygous mutations in LTBP2 have been reported in consanguineous families in which sibs have congenital Megalocornea, Ectopia Lentis, and Spherophakia.

Pedigree: 
X-linked recessive, carrier mother
X-linked recessive, father affected
Treatment
Treatment Options: 

There is no treatment for the overall condition but correction of refractive errors, cataract surgery, and low vision aids could be helpful.
 

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

X-Linked Megalocornea Caused by Mutations in CHRDL1 Identifies an Essential Role for Ventroptin in Anterior Segment Development

Webb TR, Matarin M, Gardner JC, Kelberman D, Hassan H, Ang W, Michaelides M, Ruddle JB, Pennell CE, Yazar S, Khor CC, Aung T, Yogarajah M, Robson AG, Holder GE, Cheetham ME, Traboulsi EI, Moore AT, Sowden JC, Sisodiya SM, Mackey DA, Tuft SJ, Hardcastle AJ. X-Linked Megalocornea Caused by Mutations in CHRDL1 Identifies an Essential Role for Ventroptin in Anterior Segment Development. Am J Hum Genet. 2012 Jan 24. [Epub ahead of print].

PubMed ID: 
22284829
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