arachnodactyly

Marfan Lipodystrophy Syndrome

Clinical Characteristics
Ocular Features: 

The eyes are large resulting in high myopia and apparent proptosis.  The palpebral fissures usually slant downwards and ectopia lentis may be present.  

Systemic Features: 

This syndrome shares many features of Marfan syndrome (154700) such as tall stature, dislocated lenses, myopia, high arched palate, aortic root and valvular anomalies, arachnodactyly, high arched palate, lax and hyperextensible joints, and pectus excavatum.  In addition, MFLS patients have retrognathia, intrauterine growth retardation, scarce or absent subcutaneous fat, a progeroid facies, and sometimes macrocephaly.  Postnatal growth and psychomotor development have been reported to be normal albeit with slow weight gain.

Genetics

This condition is transmitted as an autosomal dominant as the result of heterozygous mutations in FBN1 (15q21.1).  The same gene is mutated in 6 other conditions in this database including Marfan Syndrome (154700) with which it shares some features.

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

There is no treatment for the overall condition but individual features such as ectopia lentis can be surgically corrected.  Patients with high myopia require frequent evaluation for retinal tears and detachments.  Cardiac monitoring likewise is important to monitor for aortic valve prolapse and dilation of the aortic root.

References
Article Title: 

Retinitis Pigmentosa and Mental Retardation

Clinical Characteristics
Ocular Features: 

The lenses may have pleomorphic white axial opacities but in other patients can be totally opacified.  Optic atrophy is present and vision may be reduced to light perception but nystagmus is absent.  Evidence suggests that vision loss is progressive.  Some patients have extensive posterior synechiae while others have been noted to have sluggish pupils.  High myopia is a feature. The retinal pigmentation has a typical retinitis pigmentosa picture with attenuated retinal vessels and equatorial bone spicule pigmentation located in the midperiphery while the macula can have a bull’s eye appearance.   

Systemic Features: 

Early development may seem normal but developmental milestones are usually delayed.  Postnatal microcephaly and growth deficiency with mental retardation and early hypotonia are typical features.  The mental retardation may be severe.  Scoliosis and arachnodactyly have been noted and hypogonadism has been reported.  Speech may not develop and mobility is sometimes limited.

Genetics

The family pattern suggests autosomal recessive inheritance.  Homozygosity mapping has identified in a region of chromosome 8 (8q21.2-22.1) that overlaps the region for Cohen syndrome () but no specific mutated gene has been identified.      

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

None.

References
Article Title: 

Homocystinuria, Beta-Synthase Deficiency

Clinical Characteristics
Ocular Features: 

More than half of patients have ectopia lentis by the age of 10 years and the dislocation is progressive.  Ectopia lentis occurs in 90% of patients and 94% of these are noted by the age of 20 years.  The lenses seem to be more mobile than those in Marfan syndrome with a significantly increased risk of lens migration into the anterior chamber (19%) or complete dislocation into the posterior chamber (14%).   Lens surgery is required in homocystinuria about 7 years earlier than in Marfan syndrome with 62% of procedures necessitated by pupillary block glaucoma or displacement into the anterior chamber.  Whereas nearly 70% of lenses dislocate superiorly in Marfan syndrome, only 9% of homocystinuria lenses do so.

Other ocular features include optic atrophy (23%), iris atrophy (21%), anterior staphylomas (13%) and corneal opacities (9%).  Retinal detachments occur in 5-10%.  The majority of patients both pre- and postoperatively have vision of 20/50 or worse.

Systemic Features: 

Arachnodactyly and tall stature in some patients may suggest Marfan syndrome.  Mental deficiencies or behavioral problems are present in a majority of patients (50-60%) with mental functioning higher in the subset of patients who are B6-responsive.  Thromboembolic events (strokes, myocardial infarctions) are a significant risk at any age, especially so after age 20 years, and this is responsible for considerable morbidity and mortality.  The risk is especially high following general anesthesia unless hydration is strictly controlled.  Osteoporosis and seizures are common.  Hypopigmentation is often present but darkening of hair has been noted following pyridoxine treatment.  Serum homocysteine is generally elevated and the urine contains elevated levels of methionine.

Genetics

Classic homocystinuria is an autosomal recessive disorder that results from mutations in the CBS (21q22.3) gene encoding cystathionine beta-synthase.  It is the second most common error of amino acid metabolism.  Numerous mutations have been identified but among the most common ones are I278T which causes a pyridoxine-responsive disorder, and the G3307S mutation which leads to a variant that is not responsive to pyridoxine treatment.

For another more aggressive form of homocystinuria caused by mutations in MTHFR (1p36.3) see Homosystinuria, MTHER Deficiency (236250).

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Patients with this disorder form two groups: those who respond to pyridoxine (vitamin B6) and those who do not.  Those who do not respond to B6 tend to have more severe disease.  Methionine restriction administered neonatally has been reported to prevent mental retardation and reduce the rate of lens dislocation.  Neonates should be treated with B6 therapy, protein and methionine restriction, betaine, and folate with vitamin B12 supplementation.  Surgical removal of lenses may be required but the rate of vitreous loss is high.

References
Article Title: 

Stickler Syndrome, Type I

Clinical Characteristics
Ocular Features: 

High myopia and vitreous degeneration dominate the ocular manifestations of Stickler syndrome, type I.  The vitreous often appears optically empty as it liquefies and the fibrils degenerate.  The vitreous is sometimes seen to form 'veils', especially in the retrolenticular region but they may also float throughout the posterior chamber.  They are often attached to areas of lattice degeneration in the retina as well as other areas.  Posterior vitreous detachments are common.  Vitreoretinal degeneration is progressive and by the second decade rhegmatogenous detachments occur in half of affected patients.  As many as three quarters of adult patients have retinal breaks.  The retina has pigmentary changes with deposition circumferentially near the equator and more peripherally.  Hypopigmentation is more common early creating a tessellated appearance.  Lenticular opacities occur also early with cortical flecks and wedge-shaped changes.

The ERG may be normal early but evidence of rod and cone dysfunction soon appears and is progressive.  Dark adaptation is defective later in the course of the disease.  The EOG is virtually always depressed.  The visual field is constricted and may show a ring scotoma coincident with the equatorial chorioretinal atrophy.

Glaucoma is not uncommon and may be infantile in onset and difficult to control.  

Phthisis is a significant risk especially for individuals who have multiple surgical procedures for retinal detachments. 

Systemic Features: 

It has been suggested that there is a nonsyndromic or ocular type of Stickler syndrome lacking many of the extraocular features characteristic of the complete syndrome.  However, the evidence for the ocular type described here as a distinct entity remains slim and the clinical picture may simply reflect variable expressivity of mutations in the same gene.  Type I Stickler syndrome has multiple systemic features such as cleft palate, hearing impairment, premature arthritis, micrognathia, kyphoscoliosis, and some signs such as arachnodactyly that are found in the Marfan syndrome.

Genetics

This is an autosomal dominant disease of collagen formation as a result of mutations in the COL2A1 gene (12q13.11-q13.2). The mutations causing both syndromal and the suggested nonsyndromal ocular type of Stickler disease are in the same gene.  Mutations in the same gene are known to cause autosomal dominant rhegmatogenous retinal detachments in patients who have none of the systemic clinical signs (609508).  These patients may lack the signs of vitreous degeneration seen in Kniest dysplasia (156550)  and in the disorder described here.

There is better evidence for a second type of Stickler syndrome, STL2 or type II (604841) based on phenotypic differences and the fact that a second locus (1p21) containing mutations in COL11A1 has been linked to it. 

Type III is caused by mutations in COL11A2 and has systemic features similar to types I and II but lacks the eye findings since this gene is not expressed in the eye.

Type IV also has important ocular features but is an autosomal recessive disorder caused by mutations in COL9A2.

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

The combination of progressive vitreoretinal degeneration, frequency of posterior vitreous detachments, and axial myopia creates a lifelong threat of retinal tears and detachments.   Half to three quarters of all patients develop retinal tears and detachments.  Certainly all patients with Stickler syndrome deserve repeated and thorough retinal exams throughout their lives.  In addition to prompt treatment of tears and detachments, some have advocated prophylactic scleral banding to reduce vitreous traction, or applying 360 degree cryotherapy.

References
Article Title: 

Stickler syndrome in children: a radiological review

McArthur N, Rehm A, Shenker N, Richards AJ, McNinch AM, Poulson AV, Tanner J, Snead MP, Bearcroft PWP. Stickler syndrome in children: a radiological review. Clin Radiol. 2018 Apr 13. pii: S0009-9260(18)30118-1. doi: 10.1016/j.crad.2018.03.004. [Epub ahead of print].

PubMed ID: 
29661559

High efficiency of mutation detection in type 1 stickler syndrome using a two-stage approach: vitreoretinal assessment coupled with exon sequencing for screening COL2A1

Richards AJ, Laidlaw M, Whittaker J, Treacy B, Rai H, Bearcroft P, Baguley DM, Poulson A, Ang A, Scott JD, Snead MP. High efficiency of mutation detection in type 1 stickler syndrome using a two-stage approach: vitreoretinal assessment coupled with exon sequencing for screening COL2A1. Hum Mutat. 2006 Jul;27(7):696-704. Erratum in: Hum Mutat. 2006 Nov;27(11):1156.

PubMed ID: 
16752401

Marfan Syndrome

Clinical Characteristics
Ocular Features: 

Marfan syndrome typically has skeletal, ocular and cardiovascular abnormalities.  The globe is elongated creating an axial myopia and increasing the risk of rhegmatogenous retinal detachments.  Ectopia lentis is, of course, the classical ocular feature and is often if not always congenital with some progression.  The lenses most frequently dislocate superiorly and temporally and dilating the pupils often reveals broken and retracted lens zonules.  Phacodenesis and iridodenesis are commonly present even in the absence of evident lens dislocations. Cataracts develop several decades earlier than in unaffected individuals. The cornea is generally several diopters flatter than normal and there is an increased risk of open angle glaucoma.  There is considerable clinical variation among patients.

Systemic Features: 

Patients with the Marfan phenotype are usually tall with disproportionately long limbs (dolichostenomelia) and digits (arachnodactyly).   Patients frequently have scoliosis or kyphoscoliosis.  The joints are lax and hyperflexible although contractures can also occur.  The sternum is often deformed, either as a pectus excavatum, or sometimes pectus carinatum.  The hard palate is high and narrow resulting in crowding of the teeth and maloccclusion.  The defect in fibrillin is responsible for the weakness in connective tissue that leads to frequent cardiac valve malfunction, especially insufficiency of the aortic valve resulting from aortic dilatation, tear, and rupture.  The latter is often life-threatening as aortic dissection can be fatal.  Mitral valve prolapse is seen as well.  Cardiovascular disease is primarily responsible for the shortened life expectancy in this disease, more pronounced among males.

Genetics

As many as 25% of cases are caused by new mutations, but familial cases usually follow an autosomal dominant pattern of inheritance.  Autosomal recessive inheritance is claimed for several individuals in a consanguineous Turkish family.  Mutations in the fibrillin-1 gene (FBN1) on chromosome 15 (15q21.1) are considered responsible for the typical phenotype.  The exact nature of the fibrillin defect is unknown but the result is a generalized weakness in connective tissue.

The same gene is mutant in the autosomal dominant form of the Weill-Marchesani syndrome (608328) which is allelic to the Marfan syndrome.

Mutations in FBN1 have also been found in cases with isolated autosomal dominant ectopia lentis (129600).

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Isometric exercises such as weight lifting should be avoided as should contact sports in which blunt trauma to the chest may occur because of the weakened aortic wall due to cystic changes that predispose the athlete to aortic dissection.  A dislocated and/or cataractous lens may need to be removed from the visual axis, and, of course, periodic retinal examinations for retinal holes and retinal detachments should be made.   Beta-adrenergic blockade reduces the risk of aortic dilatation and improves survival.

Pravastatin has been reported to reduce aortic dilation in marfan mice.

References
Article Title: 

Pravastatin reduces marfan aortic dilation

McLoughlin D, McGuinness J, Byrne J, Terzo E, Huuskonen V, McAllister H, Black A, Kearney S, Kay E, Hill AD, Dietz HC, Redmond JM. Pravastatin reduces marfan aortic dilation. Circulation. 2011 Sep 13;124(11 Suppl):S168-73.

PubMed ID: 
21911808
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