keratoconus

Anterior Segment, Brain, and Facial Anomalies

Clinical Characteristics
Ocular Features: 

The interpupillary distance appears abnormally wide.  VEP and ERG responses suggest abnormal retinal bipolar cells.  Specular microscopy reveals variable sizes and shapes of corneal endothelial cells with scattered vesicles and large 'holes' in the usual hexagonal array.  The iris may be malformed (no collarette, stromal hypoplasia) and there may be peripheral iridocorneal adhesions.  Elevated IOP, band keratopathy, corneal clouding, and keratoconus have been reported.  Visual acuity is impaired to some extent, from near normal (20/25) to NLP.  Progressive optic atrophy was observed in one patient.

Systemic Features: 

Four members of a 3 generation family had malformed pinnae (posterior placement and rotation).  Other features variably present were an empty sella turcica, posterior fossa cyst, and hydrocephalus. The propositus also was found to have abnormal auditory bipolar cells based on the audiogram and audio-evoked brainstem responses.

Genetics

Based on direct sequencing in one family (3 adults and 1 child), this condition seems to be caused by heterozygous variations or mutations in the VSX1 gene (20p11.21). 

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Monitoring for glaucoma and appropriate treatment are indicated.  Hearing tests should be performed early.  The usual treatments for keratoconus should be considered.  Excess brain fluid may need surgical drainage.

.

References
Article Title: 

Cranial Dysinnervation Disorders with Strabismus and Arthrogryposis

Clinical Characteristics
Ocular Features: 

Strabismus and/or ophthalmoplegia are important features of a group of conditions known as cranial dysinnervation disorders.  Ptosis, Duane syndrome, V pattern exotropia and various degrees of ophthalmoplegia may be seen.  There may be considerable asymmetry in the manifestations in the two eyes.  Epicanthal folds, blepharophimosis, and hypermetropia are sometimes present.  Some patients have corneal leukomas, keratoglobus, high corneal astigmatism, and dysplastic optic disks. 

A pigmentary retinopathy and folds in the macula with an abnormal ERG has been reported.  Subnormal vision has been reported in some patients.

Systemic Features: 

Patients are often short in stature with pectus excavatum, spine stiffness, highly arched palate, and club feet.  Limited forearm rotation and wrist extension may be present.  The fingers appear long and often have contractures while the palmar and phalangeal creases may be absent.  Camptodactyly and clinodactyly are common.  Deep tendon reflexes are often hyporeactive and decreased muscle mass has been noted.  The muscles seem "firm" to palpation.  Restrictive lung disease has been reported.  Hearing loss is experienced by some individuals.

Genetics

Distal arthrogryposis type 5D is caused by homozygous or compound heterozygous mutations in the ECEL1 gene located at 2q36.  However, a similar phenotype (albeit with more severe ocular manifestations) results from heterozygous mutations in PIEZO2 (18p11).  Heterozygous mutations in the PIEZO2 gene have also been reported to cause distal arthrogryposis type 3 (Gordon syndrome [114300]) and Marden-Walker syndrome (248700) and all of these may be simply phenotypical variations of the same disorder.

Pedigree: 
Autosomal dominant
Autosomal recessive
Treatment
Treatment Options: 

There is no treatment for this condition.  Patients with subnormal vision may benefit from low vision aids and selective surgery may be helpful in reducing the physical restrictions from physical deformities.

References
Article Title: 

Mutations in PIEZO2 cause Gordon syndrome, Marden-Walker syndrome, and distal arthrogryposis type 5

McMillin MJ, Beck AE, Chong JX, Shively KM, Buckingham KJ, Gildersleeve HI, Aracena MI, Aylsworth AS, Bitoun P, Carey JC, Clericuzio CL, Crow YJ, Curry CJ, Devriendt K, Everman DB, Fryer A, Gibson K, Giovannucci Uzielli ML, Graham JM Jr, Hall JG, Hecht JT, Heidenreich RA, Hurst JA, Irani S, Krapels IP, Leroy JG, Mowat D, Plant GT, Robertson SP, Schorry EK, Scott RH, Seaver LH, Sherr E, Splitt M, Stewart H, Stumpel C, Temel SG, Weaver DD, Whiteford M, Williams MS, Tabor HK, Smith JD, Shendure J, Nickerson DA; University of Washington Center for Mendelian Genomics, Bamshad MJ. Mutations in PIEZO2 cause Gordon syndrome, Marden-Walker syndrome, and distal arthrogryposis type 5. Am J Hum Genet. 2014 May 1;94(5):734-44.

PubMed ID: 
24726473

GAPO Syndrome

Clinical Characteristics
Ocular Features: 

Progressive optic atrophy is considered part of this syndrome but it is not a consistent feature.  One patient with the suspected diagnosis had papilledema while other individuals may have congenital glaucoma, buphthalmos, band keratopathy, and keratoconus.  White eyelashes have been described.  Myelinated nerve retinal nerve fibers may be prominent.

Systemic Features: 

This is a rare congenital disorder with so far incomplete phenotypic delineation. The diagnosis can be made soon after birth from the general facial and body morphology.  The dysmorphism is secondary to marked bone growth retardation and metaphyseal dysplasia, resulting in a flat midface, frontal bossing, micrognathism, chest deformities, and vertebral anomalies. Psychomotor retardation is common but the extent of cognitive deficits is unknown.  The permanent teeth may begin to develop but fail to erupt (pseudoanodontia). Even primary dentition is often abnormal.  Alopecia is a feature although some individuals do have sparse body hair, at least for a period of time.  Anomalous blood vessels such as dilated scalp veins are sometimes evident.   Hypogonadism has been reported in both sexes.  Individuals are subject to recurrent ear and respiratory infections. 

Genetics

GAPO occurs in both sexes.  Homozygous mutations in the ANTXR1 gene (2p13.3) are responsible for this disorder.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Treatment is directed at individual problems.  Prompt treatment of respiratory infections is important.

References
Article Title: 

Mutations in ANTXR1 cause GAPO syndrome

Stranecky V, Hoischen A, Hartmannova H, Zaki MS, Chaudhary A, Zudaire E, Noskova L, Baresova V, Pristoupilova A, Hodanova K, Sovova J, Hulkova H, Piherova L, Hehir-Kwa JY, de Silva D, Senanayake MP, Farrag S, Zeman J, Martasek P, Baxova A, Afifi HH, St Croix B, Brunner HG, Temtamy S, Kmoch S. Mutations in ANTXR1 cause GAPO syndrome. Am J Hum Genet. 2013 May 2;92(5):792-9.

PubMed ID: 
23602711

Ophthalmic findings in GAPO syndrome

Ilker SS, Ozturk F, Kurt E, Temel M, Gul D, Sayli BS. Ophthalmic findings in GAPO syndrome. Jpn J Ophthalmol. 1999 Jan-Feb;43(1):48-52.

PubMed ID: 
10197743

Williams Syndrome

Clinical Characteristics
Ocular Features: 

Blue irides (77%) and a lacey or stellate pattern (74%) of the iris are characteristic.  The stroma appears coarse with radial or cartwheel striations.  The iris collarette is usually absent or anomalous.  Features of the Peters' anomaly may be present.  The periorbital tissues are described as 'full' and prominent.  Strabismus (usually esotropia) occurs in more than half of patients.  Retinal vessel tortuosity is present in 22% of patients.  Cataracts may be found in younger individuals but are uncommon. Hyperopia is the most common refractive error.  Keratoconus has been described in at least 3 patients.

Systemic Features: 

The phenotype is variable, likely depending upon the size of the deletion.  Cardiovascular disease, primarily hypertension and large vessel stenosis, are among the most important features.  The elastin arteriopathy lead to thickened arterial walls with peripheral pulmonary stenosis and supravalvular aortic stenosis.  The facies is considered unique with bitemporal narrowing, a wide mouth, full lips, malocclusion, small jaw, and prominent earlobes.  The teeth are small and widely spaced.  Connective tissue abnormalities include joint hyperextensibility, hernias, lax skin, hypotonia, and bowel/bladder diverticulae.  Small birth size is common and infants often fail to thrive but at puberty patients can experience a growth spurt.  Ultimate height in adults is usually in the third centile.

Vocal cord anomalies and paralysis can result in a hoarse voice.  A sensorineural hearing loss is common among adults but hyperacusis is often present in young children.

Hypercalcemia and hypercalciuria are common and some (10%) have hypothyroidism.

Most individuals have some cognition difficulties and delays but normal intelligence has also been reported.  Patient personalities consist of anxiety, attention deficit disorder, marked friendliness and a high level of empathy.  Visiospatial construction is often impaired.  Most adults are unable to live independently.

Genetics

This is a deletion syndrome but included in this database because the major features are due to the loss of a single gene (ELN).  The deletion segment consists of 1.4-1.8 Mb at 7q11.23 containing as many as 28 genes.   Most cases occur sporadically but parent-child transmission and affected siblings have been reported.  The recurrence risk is low.

Increased tortuosity of the retinal arterioles is also a feature of Fabry disease (301500) and of a condition known as isolated retinal arteriolar tortuosity (611773, 180000).

Treatment
Treatment Options: 

Feeding issues should be addressed early in infants who fail to thrive.  Early intervention with speech and physical therapy plus special education can be helpful.  Psychological evaluations may help in managing behavioral issues.

Hypertension can often be managed medically but surgery may be required for vascular stenoses.   Hypercalcemia and hypothyroidism often respond to medical therapy. Strabismus, vessel narrowing, and valvular malfunctions can be treated surgically.

References
Article Title: 

The iris in Williams syndrome

Holmstrom G, Almond G, Temple K, Taylor D, Baraitser M. The iris in Williams syndrome. Arch Dis Child. 1990 Sep;65(9):987-9.

PubMed ID: 
2221973

Ocular findings of Williams' syndrome

Hotta Y, Kishishita H, Wakita M, Inagaki Y, Momose T, Kato K. Ocular findings of Williams' syndrome. Acta Paediatr Scand. 1990 Aug-Sep;79(8-9):869-70.

PubMed ID: 
2239289

Gurrieri Syndrome

Clinical Characteristics
Ocular Features: 

Tapetoretinal degeneration has been described in several patients.  Some patients have keratoconus with lens and corneal opacities.  Visual acuities have not been reported.  The full ocular phenotype must be considered unknown since most patients have not had full ophthalmic evaluations.

Systemic Features: 

Features of an osteodysplasia are among the most striking in this syndrome.  Short stature, brachydactyly, delayed bone age, osteoporosis, and hypoplasia of the acetabulae and iliac alae are usually present.  Birth weight is often low.  Joints may be hyperflexible as part of the generalized hypotonia. The eyes are deep-set, the nasal bridge is prominent, the midface is flat, and the supraorbital ridges are prominent giving the face a rather coarse look.  Prognathism with a prominent lower lip and dental malocclusion reinforce this appearance.  Seizures beginning in early childhood may be difficult to control.  Most patients have severe psychomotor retardation and never acquire speech.

Genetics

The genetics of this familial disorder remain unknown.  No locus or mutation has been identified but one patient had an absent maternal allele of the proximal 15q region as found in Angelman syndrome.

Orofaciodigital syndrome IX (258865) is another autosomal recessive syndrome sometimes called Gurrieri syndrome.  In Gurrieri’s original description of two brothers, chorioretinal lacunae, similar to those seen in Aicardi syndrome (304050), were present.  The systemic features are dissimilar, however.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment is known.

References
Article Title: 

Brittle Cornea Syndrome 2

Clinical Characteristics
Ocular Features: 

Corneal thinning and extreme fragility are characteristic of BCS2.  Ruptures of the cornea may occur with minimal trauma and repair is often unsatisfactory due to the lack of healthy tissue.  Keratoconus, acute hydrops, keratoglobus, and high myopia are frequently present as well.  Some patients have sclerocornea that obscures the normal limbal landmarks.  The sclera is also thin and the underlying pigmented uveal tissue imparts a bluish discoloration to the globe which is especially evident in the area overlying the ciliary body creating what some call a blue halo.

Systemic Features: 

Skin laxity with easy bruisability, pectus excavatum, scoliosis, congenital hip dislocation, a high arched palate, mitral valve prolapse and recurrent shoulder dislocations are often present.  Hearing impairment with mixed sensorineural/conductive defects is common.

Genetics

This autosomal recessive disorder results from homozygous mutations in PRDM5 (4q27).  Heterozygous carriers may have blue sclerae, small joint hypermobility, and mild thinning of the central cornea. 

BCS2 has many clinical similarities to brittle cornea syndrome 1 (229200) which results from homozygous mutations in ZNF469.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Treatment for specific defects such as joint dislocations and mitral valve malfunction may be helpful.

References
Article Title: 

Brittle cornea syndrome: recognition, molecular diagnosis and management

Burkitt Wright EM, Porter LF, Spencer HL, Clayton-Smith J, Au L, Munier FL, Smithson S, Suri M, Rohrbach M, Manson FD, Black GC. Brittle cornea syndrome: recognition, molecular diagnosis and management. Orphanet J Rare Dis. 2013 May 4;8(1):68. [Epub ahead of print]

PubMed ID: 
23642083

Mutations in PRDM5 in brittle cornea syndrome identify a pathway regulating extracellular matrix development and maintenance

Burkitt Wright EM, Spencer HL, Daly SB, Manson FD, Zeef LA, Urquhart J, Zoppi N, Bonshek R, Tosounidis I, Mohan M, Madden C, Dodds A, Chandler KE, Banka S, Au L, Clayton-Smith J, Khan N, Biesecker LG, Wilson M, Rohrbach M, Colombi M, Giunta C, Black GC. Mutations in PRDM5 in brittle cornea syndrome identify a pathway regulating extracellular matrix development and maintenance. Am J Hum Genet. 2011 Jun 10;88(6):767-77. Erratum in: Am J Hum Genet. 2011 Aug 12;89(2):346.

PubMed ID: 
21664999

Leber Congenital Amaurosis

Clinical Characteristics
Ocular Features: 

Leber congenital amaurosis is a collective term applied to multiple recessively inherited conditions with early-onset retinal dystrophy causing infantile or early childhood blindness.  There are no established diagnostic criteria.  First signs are usually noted before the age of 6 months.  These consist of a severe reduction in vision accompanied by nystagmus, abnormal pupillary responses, and photophobia.  Ametropia in the form of hyperopia is common.  Keratoconus (and keratoglobus) is frequently found in older children but it is uncertain if this is a primary abnormality or secondary to eye rubbing as the latter is commonly observed.  Repeated pressure on the eye may also be responsible for the relative enophthalmos often seen in these patients.  The ERG is reduced or absent early and permanently.  Final visual acuity is seldom better than 20/400 and perhaps one-third of affected individuals have no light perception.  Some individuals experience a period of vision improvement.

The retina usually has pigmentary changes but these are not diagnostic.  Retinal vessels are generally attenuated.  The RPE may have a finely granulated appearance or, in some cases, whitish dots, and even 'bone spicules'.

Systemic Features: 

A variety of metabolic and physical abnormalities have been reported with LCA but many publications are from the pre-genomic era and the significance of such associations remains uncertain.  Most extraocular signs result from delays in mental development but it is uncertain what role, if any, that visual deprivation plays.  Perhaps 20% of patients are mentally retarded or have significant cognitive deficits.

Genetics

Leber congenital amaurosis is genetically heterogeneous with at least 18 known gene mutations associated with the phenotype.  It is also clinically heterogeneous both within and among families and this is the major obstacle to the delineation of individual clinicogenetic entities.  As more patients are genotyped, it is likely that more precise genotype-phenotype correlations will emerge.  At the present time, however, it is not possible to use clinical findings alone to distinguish individual conditions.

Below are links to the genotypic and phenotypic features of the 19 known types of LCA.  All cause disease in the homozygous or compound heterozygous state. 

LCA type               OMIM#                 Locus              Gene Symbol   

LCA 1                    204000                 7p13.1                 GUCY2D

LCA 2                    204100                 1p31                    RPE65**

LCA 3                    604232                 14q31.3               SPATA7

LCA 4                    604393                 17p13.1               AIPL1

LCA 5                    604537                 6q14.1                 LCA5

LCA 6                    613826                 14q11                  RPGRIP1

LCA 7                    613829                19q13.1                CRX*

LCA 8                    613835                 1q31-q32             CRB1

LCA 9                    608553                 1p36                    NMNAT1

LCA 10                  611755                 12q21                  CEP290

LCA 11                  613837                 7q31.3-q332        IMPDH1

LCA 12                  610612                 1q32.3                 RD3

LCA 13                  612712                 14q24.1               RDH12

LCA 14                  613341                 4q31                    LRAT

LCA 15                  613843                 6p21-31              TULP1

LCA 16                  614186                 2q37                    KCNJ13

LCA 17                  615360                 8q22.1                 GDF6

LCA 18                  608133                 6p21.1                 PRPH2***

It is likely that more mutant genes will be identified since these are found in only about half of patients studied in large series.  

*(Heterozygous mutations in CRX may also cause a cone-rod dystrophy).

**(Mutations in RPE65 has been described as also causing retinitis pigmentosa (RP20; 613794)  with choroidal involvement.)

***Mutations in PRPH2 (RDS) has also been reported to cause retinitis pigmentosa 7, choroidal dystrophy, and vitelliform macular dystrophy (179605) among others.

See also Leber Congenital Amaurosis with Early-Onset Deafness.

Mutations in the GUCY2D gene seem to be the most common being present in about 21% of LCA patients with CRB1 next at 10%.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Until recently, no treatment was available for LCA.  However, results from early clinical trials with adeno-associated virus vector mediated gene therapy for RPE65 mutations in LCA 2 show promise.  Subretinal placement of recombinant  adeno-virus carrying RPE65 complementary DNA results in both subjective and objective improvements in visual function.  Patients generally report subjective improvement in light sensitivity and visual mobility.  Some recovery of rod and cone photoreceptor function has been documented.  Studies have also documented an improvement in visual acuity, size of visual field, pupillary responses, and in the amouunt of nystagmus.  More than 230 patients have now  been treated and improvements seem to be maintained for at least 3 or more years.  However, we have also learned that along with the enzymatic dysfunction of RPE65 that disrupts the visual cycle, there is also degeneration of photoreceptors which continues after treatment and the long term prognosis remains guarded. Multiple phase I clinical trials have demonstrated the safety of this approach and phase III trials are now underway.

It is crucial for patients to be enrolled early in sensory stimulation programs to ensure optimum neural development.  For patients with residual vision, low vision aids can be beneficial.  Vocational and occupational therapy should be considered for appropriate patients.

References
Article Title: 

Mutations in NMNAT1 cause Leber congenital amaurosis and identify a new disease

Koenekoop RK, Wang H, Majewski J, Wang X, Lopez I, Ren H, Chen Y, Li Y,
Fishman GA, Genead M, Schwartzentruber J, Solanki N, Traboulsi EI, Cheng J, Logan
CV, McKibbin M, Hayward BE, Parry DA, Johnson CA, Nageeb M; Finding of Rare
Disease Genes (FORGE) Canada Consortium, Poulter JA, Mohamed MD, Jafri H, Rashid
Y, Taylor GR, Keser V, Mardon G, Xu H, Inglehearn CF, Fu Q, Toomes C, Chen R.
Mutations in NMNAT1 cause Leber congenital amaurosis and identify a new disease
pathway for retinal degeneration. Nat Genet. 2012 Jul 29.
 

PubMed ID: 
22842230

A dominant mutation in RPE65 identified by whole-exome sequencing causes retinitis pigmentosa with choroidal involvement

Bowne SJ, Humphries MM, Sullivan LS, Kenna PF, Tam LC, Kiang AS, Campbell M, Weinstock GM, Koboldt DC, Ding L, Fulton RS, Sodergren EJ, Allman D, Millington-Ward S, Palfi A, McKee A, Blanton SH, Slifer S, Konidari I, Farrar GJ, Daiger SP, Humphries P. A dominant mutation in RPE65 identified by whole-exome sequencing causes retinitis pigmentosa with choroidal involvement. Eur J Hum Genet. 2011 Oct;19(10):1074-81. Erratum in: Eur J Hum Genet. 2011 Oct;19(10):1109.

PubMed ID: 
21654732

Treatment of leber congenital amaurosis due to RPE65 mutations by ocular subretinal injection of adeno-associated virus gene vector: short-term results of a phase I trial

Hauswirth WW, Aleman TS, Kaushal S, Cideciyan AV, Schwartz SB, Wang L, Conlon TJ, Boye SL, Flotte TR, Byrne BJ, Jacobson SG. Treatment of leber congenital amaurosis due to RPE65 mutations by ocular subretinal injection of adeno-associated virus gene vector: short-term results of a phase I trial. Hum Gene Ther. 2008 Oct;19(10):979-90.

PubMed ID: 
18774912

Effect of gene therapy on visual function in Leber's congenital amaurosis

Bainbridge JW, Smith AJ, Barker SS, Robbie S, Henderson R, Balaggan K, Viswanathan A, Holder GE, Stockman A, Tyler N, Petersen-Jones S, Bhattacharya SS, Thrasher AJ, Fitzke FW, Carter BJ, Rubin GS, Moore AT, Ali RR. Effect of gene therapy on visual function in Leber's congenital amaurosis. N Engl J Med. 2008 May 22;358(21):2231-9.

PubMed ID: 
18441371

Leber congenital amaurosis

Perrault I, Rozet JM, Gerber S, Ghazi I, Leowski C, Ducroq D, Souied E, Dufier JL, Munnich A, Kaplan J. Leber congenital amaurosis. Mol Genet Metab. 1999 Oct;68(2):200-8. Review.

PubMed ID: 
10527670

Keratoconus 4

Clinical Characteristics
Ocular Features: 

The cornea progressively thins in the lower portion, usually in juveniles and young adults.  The cornea may appear normal by slit lamp examination in early stages but keratoscopy can show steepening or distortion of the mires.  Retinoscopy through dilated pupils often yields a ‘scissoring’ pattern.  Early symptoms include uncorrectable blurring of vision and visual distortion.  The central and lower cornea progressively thins with formation of a cone.  A subepithelial iron line can sometimes be seen around the conical portion of the cornea (Fleischer ring).  Vertical lines may be found in the deep portions of the stroma and in Descemet membrane (Vogt striae).  The disease can progress for some years but there may also be periods of stability.  Individuals with advanced disease may suffer acute painful episodes following breaks in the Descemet membrane with edema and opacification in the cone (hydrops), followed by stromal scarring.

Systemic Features: 

Keratoconus has been found in a large number of systemic conditions, such as connective tissue disorders, Down syndrome, and chromosomal disorders.  It has been blamed on eye rubbing as is often seen in Leber congenital amaurosis and other ocular disorders as well as in atopic conditions and in individuals who have worn contact lenses for many years.  Cause and effect in these situations is difficult to prove and it is likely that keratoconus is an etiologically heterogeneous disorder.  Only keratoconus associated with single gene mutations are considered here.

Recent evidence suggests that corneal hydrops is strongly associated with mitral valve prolapse. 

Genetics

Less than 10% of keratoconus cases have a positive family history and several mutations seem to be responsible.  Mutations at the 2p24 locus on chromosome 2 seem to cause KTCN4 based on genome-wide linkage analysis in families from multiple out-bred populations.  The pattern of inheritance is autosomal dominant.

Other forms of hereditary keratoconus caused by different mutations are:  Mutations in VSX1 (20p11.2) cause KTCN1, KTCN2 (608932) is linked to a mutation on chromosome 16 (16q22.3-q23.1), and KTCN3 (608586) results from a mutation on chromosome 3 (3p14-q13).

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Contact lenses may correct vision satisfactorily in early stages of the disease but up to 20% of patients will eventually need a corneal transplant.

References
Article Title: 

Keratoconus 3

Clinical Characteristics
Ocular Features: 

The cornea progressively thins in the lower portion, usually in juveniles and young adults.  The cornea may appear normal by slit lamp examination in early stages but keratoscopy can show steepening or distortion of the mires.  Retinoscopy through dilated pupils often yields a 'scissoring' pattern.  Early symptoms include uncorrectable blurring of vision and visual distortion.  The central and lower cornea progressively thins with formation of a cone.  A subepithelial iron line can sometimes be seen around the conical portion of the cornea (Fleischer ring).  Vertical lines may be found in the deep portions of the stroma and in Descemet membrane (Vogt striae).  The disease can progress for some years but there may also be periods of stability.  Individuals with advanced disease may suffer acute painful episodes following breaks in the Descemet membrane with edema and opacification in the cone (hydrops), followed by stromal scarring.

Systemic Features: 

Keratoconus has been found in a large number of systemic conditions, such as connective tissue disorders, Down syndrome, and chromosomal disorders.  It has been blamed on eye rubbing as is often seen in Leber congenital amaurosis and other ocular disorders as well as in atopic conditions and in individuals who have worn contact lenses for many years.  Cause and effect in these situations is difficult to prove and it is likely that keratoconus is an etiologically heterogeneous disorder.  Only keratoconus associated with single gene mutations are considered here.

Recent evidence suggests that corneal hydrops is strongly associated with mitral valve prolapse. 

Genetics

Less than 10% of keratoconus cases have a positive family history and several mutations seem to be responsible.  KTCN3 seems to be caused by a mutation located at 3p14-q13 as determined from linkage studies in a 2 generation Italian family.  It is inherited in an autosomal dominant pattern.

Other forms of hereditary keratoconus caused by different mutations are:  KTCN1 (148300) caused by mutations in the VSX1 gene at 20p11.2), KTCN2 (608932) from a mutation on chromosome 16 (16q22.3-q23.1), and KTCN4 (609271) caused by a mutation on chromosome 2 (2p24).

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Contact lenses may correct vision satisfactorily in early stages of the disease but up to 20% of patients will eventually need a corneal transplant.

References
Article Title: 

Keratoconus 2

Clinical Characteristics
Ocular Features: 

The cornea progressively thins in the lower portion, usually in juveniles and young adults.  The cornea may appear normal by slit lamp examination in early stages but keratoscopy can show steepening or distortion of the mires.  Retinoscopy through dilated pupils often yields a 'scissoring' pattern.  Early symptoms include uncorrectable blurring of vision and visual distortion.  The central and lower cornea progressively thins with formation of a cone.  A subepithelial iron line can sometimes be seen around the conical portion of the cornea (Fleischer ring).  Vertical lines may be found in the deep portions of the stroma and in Descemet membrane (Vogt striae).  The disease can progress for some years but there may also be periods of stability.  Individuals with advanced disease may suffer acute painful episodes following breaks in the Descemet membrane with edema and opacification in the cone (hydrops), followed by stromal scarring.

Systemic Features: 

Keratoconus has been found in a large number of systemic conditions, such as connective tissue disorders, Down syndrome, and chromosomal disorders.  It has been blamed on eye rubbing as is often seen in Leber congenital amaurosis and other ocular disorders as well as in atopic conditions and in individuals who have worn contact lenses for many years.  Cause and effect in these situations is difficult to prove and it is likely that keratoconus is an etiologically heterogeneous disorder.  Only keratoconus associated with single gene mutations are considered here.

Recent evidence suggests that corneal hydrops is strongly associated with mitral valve prolapse. 

Genetics

Less than 10% of keratoconus cases have a positive family history and several mutations seem to be responsible.  KTCN2 seems to be caused by a mutation located at 16q22.3-q23.1 as determined from linkage studies in 20 Finnish families.  It is inherited in an autosomal dominant pattern.

Other forms of hereditary keratoconus caused by different mutations are:  KTCN1 (148300) caused by a mutation in the VSX1 gene (20p11.2), KTCN3 (608586) from a mutation on chromosome 3 (3p14-q13), and KTCN4 (609271) caused by a mutation on chromosome 2 (2p24).

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Contact lenses may correct vision satisfactorily in early stages of the disease but up to 20% of patients will eventually need a corneal transplant.

References
Article Title: 

Pages

Subscribe to RSS - keratoconus