rod-cone dystrophy

Retinal Dystrophy with or without Macular Staphyloma

Clinical Characteristics
Ocular Features: 

Few patients have had complete eye studies and physical findings are seemingly limited to the eye.  Patients complain of progressively decreasing vision as early as the first decade of life.  Abnormal retinal findings may be present by the second decade and maybe earlier.  The RPE can appear mottled and the retinal vessels are attenuated.  Retinal pigment clumping occurs later.  Night blindness and visual field constriction occur.  Cone and flicker ERGs may be nonrecordable while rod and flash ERGs are reduced consistent with a rod-cone dystrophy.  The retinal lamination has been described as abnormal on OCT in some individuals.

Macular staphylomas have been described in three unrelated offspring of consanguineous parents.

Vision loss is severe with legal blindness by midlife and one patient lost light perception by 40 years of age.  

Systemic Features: 

No consistent systemic abnormalities have been reported.

Genetics

Homozygous or compound heterozygous mutations in the C21orf2 gene (21q22.3) are the cause of this autosomal recessive syndrome.

Homozygous or heterozygous mutations in the same gene are responsible for axial spondylometaphyseal dysplasia (602271).

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment has been reported.

References
Article Title: 

Alström Syndrome

Clinical Characteristics
Ocular Features: 

Progressive failure of rods and cones begins in the first year of life and inevitably leads to blindness.  Central vision is lost first and nystagmus in early childhood results.   Photophobia can be evident in the first year of life.  Early ERGs show severe impairment of cone responses with little or no rod dysfunction.  In the second and third decades all rod and cone responses are extinguished.  Vision can be less than 20/400 by the age of 10 years and usually all light perception is lost by the beginning of the third decade.  Pale optic nerves with retinal arteriorlar narrowing and posterior subcapsular cataracts have been seen.

Systemic Features: 

This is a multisystem disease with onset in the first year of life.  Infants may have a normal birth weight but develop truncal obesity in the first year.  Hearing loss is evident in the first decade.  Insulin resistant type 2 diabetes mellitus with hyperinsulinemia often occurs in childhood and may be accompanied by hypothyroidism and hypogonadotropic hypogonadism.  Acanthosis nigricans and some degree of pulmonary dysfunction are common.  The majority of individuals (70%) develop restrictive or dilated cardiomyopathy, many in the first months of life, resulting in cardiac failure.  The liver may become cirrhotic and renal failure occurs late.  Intelligence is usually normal but many patients (25-30%) have early delays in their developmental milestones perhaps secondary to growth hormone deficiency which has been reported (98% are short in stature).  Lifespan is short and many die in childhood.  Few live beyond the age of 40 years.

Alstrom syndrome has some similarities to Bardet-Biedl syndrome (209900) but differs in the absence of mental deficiency and polydactyly.

Genetics

This is an autosomal recessive disorder resulting from homozygous mutations in the ALMS1 gene on chromosome 2 (2p13).  The ALMS1 protein product is found in many cells throughout the body and is located in centrosomes and the base of cilia.  Its function is unknown.

More than 320 mutations have been reported. However, many cases remain in which no mutation has been found suggesting additional genetic heterogeneity remains.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment is available for the basic disease.

References
Article Title: 

Alström Syndrome: Mutation Spectrum of ALMS1

Marshall JD, Muller J, Collin GB, Milan G, Kingsmore SF, Dinwiddie D, Farrow EG, Miller NA, Favaretto F, Maffei P, Dollfus H, Vettor R, Naggert JK. Alstrom Syndrome: Mutation Spectrum of ALMS1. Hum Mutat. 2015 Apr 2. doi: 10.1002/humu.22796. [Epub ahead of print].

PubMed ID: 
25846608

Alström syndrome

Marshall JD, Beck S, Maffei P, Naggert JK. Alstrom syndrome. Eur J Hum Genet. 2007 Dec;15(12):1193-202.

PubMed ID: 
17940554

Retinal Dystrophy, Newfoundland Type

Clinical Characteristics
Ocular Features: 

There is considerable clinical heterogeneity, mostly age-dependent.  Night blindness can occur in early childhood but usually later even though scotopic responses can be undetectable in the first decade of life while photopic responses are reduced on the ERG at all ages.  Both rod and cone responses may be extinguished in later life.  Visual acuity can be decreased beginning in early childhood and legal blindness usually occurs by the second or third decade of life.  However, the loss of vision continues to progress and severe vision loss to finger-counting may be present in older individuals.  A scallop-bordered lacunar atrophy may be seen in the midperiphery.  The macula is only mildly involved by clinical examination although central retinal thinning is seen in all cases.  Dyschromatopsia is mild early and usually becomes more severe.  The visual fields are moderately to severely constricted although in younger individuals a typical ring scotoma is present.  The peripheral retina contains ‘white dots’ and often resembles the retinal changes seen in retinitis punctate albescens.

Systemic Features: 

None reported.

Genetics

Homozygous mutations in the RLBP1 gene (15q26.1) are responsible for this disorder.  Homozygous mutations in RLBP1 have also been found among patients with fundus albipunctatus (136880), retinitis punctata albescens, and in Bothnia type retinal dystrophy (607475),

NFRCD clinically resembles Bothnia type retinal dystrophy (607475) which likewise results from mutations in the RLBP1 gene but the maculae appear normal or have only a mild ‘beaten-bronze’ atrophy.

See Flecked Retina entry for somewhat similar conditions.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment is known.

References
Article Title: 

Retinal Dystrophy and Obesity

Clinical Characteristics
Ocular Features: 

The age of onset of symptoms is unknown but based on the report of a single family with three affected sibs, it may occur early in the second decade. Patients may note some loss of night vision and the visual fields are restricted.  The ERG responses are consistent with a generalized rod-cone dystrophy.  Fundoscopy reveals a generalized RPE atrophy together with arteriolar attenuation, peripheral pigmentary mottling and scattered white dots.  A nonspecific dyschromatopsia can be demonstrated but the fovea is relatively normal and central acuity is remarkably good.  Little is known about disease progression but an 18 year old male reported decreasing vision since the age of 11 years.  

Systemic Features: 

Obesity and a high BMI may be present.

Genetics

Homozygous mutations in the TUB gene (11p15) segregated with this disorder in a sibship from a consanguineous family.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment has been reported.

References
Article Title: 

Retinitis Pigmentosa 38

Clinical Characteristics
Ocular Features: 

This is a rare clinically heterogeneous condition in which both rods and cones functions are variably affected.  It is a progressive disorder with children often being aware of night vision difficulties during the latter half of the first decade of life.  Reduced vision is often present at this time as well and progressively deteriorates.  Visual fields are constricted to 20-30 degrees.  Rod responses may be nondetectable in the first decade.

Central vision is subnormal as early as childhood and progressively worsens with age.  Dyschromatopsia to some degree is often present early as well and some patients have a maculopathy with a bull’s eye pattern and thinning of the photoreceptor layer seen on OCT.  Attenuated retinal vessels, pale optic discs, and variable fundus pigmentary changes (including pigmentary mottling and bone spicules) have been seen.  The degree and course of the photoreceptor damage is variable leading some to propose that RP38 is primarily a cone-rod dystrophy.

Systemic Features: 

None

Genetics

This is an autosomal recessive disorder resulting from homozygous mutations in the MERTK gene (2q13).

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment has been reported but young people especially could benefit from low vision aids and special education therapy.

References
Article Title: 

Retinitis Pigmentosa, Hearing Loss, Ataxia, Cataract, and Polyneuropathy

Clinical Characteristics
Ocular Features: 

Cataracts and a pigmentary retinopathy occur in this condition but only in some, primarily older, patients.  The lens opacities progress and may become visually significant by the third decade.  Bone-spicule-shaped pigment clumping may be present in the midperiphery while the optic disk is often pale and the retinal vessels are attenuated. The ERG responses are consistent with a rod-cone dystrophy.

Systemic Features: 

This is a progressive neurological disorder with onset of signs and symptoms in childhood although full expression may not occur until adulthood.  Young children can have hyporeflexia, pes cavus, spasticity, and gait ataxia.  A sensorineural hearing loss may also be present in childhood but sometimes not until later.  Hyperreflexia with extensor plantar responses and Achilles tendon contractures are often present later.  The peripheral polyneuropathy is predominantly demyelinating with both sensory and motor components and is present in all adults.  Cerebellar atrophy, primarily in the vermis, can be demonstrated on MRI examination.  Mental function is usually not impaired. Some patients have dysarthria. 

This disorder has some clinical similarities to Refsum disease (266500).

Genetics

This is an autosomal recessive disorder resulting from homozygous mutations in the ABHD12 gene (20p11.21).

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Treatment is directed at symptoms.  Visually significant cataracts may require removal.  Low vision aids and physical therapy can be helpful.

References
Article Title: 

Mutations in ABHD12 cause the neurodegenerative disease PHARC: An inborn error of endocannabinoid metabolism

Fiskerstrand T, H'mida-Ben Brahim D, Johansson S, M'zahem A, Haukanes BI, Drouot N, Zimmermann J, Cole AJ, Vedeler C, Bredrup C, Assoum M, Tazir M, Klockgether T, Hamri A, Steen VM, Boman H, Bindoff LA, Koenig M, Knappskog PM. Mutations in ABHD12 cause the neurodegenerative disease PHARC: An inborn error of endocannabinoid metabolism. Am J Hum Genet. 2010 Sep 10;87(3):410-7.

PubMed ID: 
20797687

Retinal Dystrophy, Bothnia Type

Clinical Characteristics
Ocular Features: 

Night blindness occurs from early childhood when the fundus still appears normal.  However, rod responses may be absent from ERG recordings even in the first decade and this is followed by loss of cone responses in older individuals. Rod responses can recover after prolonged dark adaptation but cone function does not recover.  Multifocal ERGs can detect early deterioration of the macula while vision and the appearance of the macula are still normal.

Pigment deposition can sometimes be seen in the retina and the retinal blood vessels may be attenuated.  In young adults the fundus may have the appearance of retinitis albescens but eventually changes resembling central areolar atrophy develop in the macula.  Retinal thinning in the fovea and parafoveal areas has been described.  Progressive loss of vision leads to legal blindness in early adulthood.  The peripheral retina undergoes degenerative changes as well.

Systemic Features: 

No extraocular abnormalities have been reported.

Genetics

Homozygous mutations in the RLBP1 gene (15q26.1) have been identified in patients with Bothnia retinal dystrophy.  The protein product is essential to the proper function of both rod and cone photoreceptors.  When defective the normal cycling of retinoids between RPE cells and photoreceptors is disrupted, thereby negatively impacting what is sometimes called the 'visual cycle'. 

This rod-cone dystrophy has a high prevalence in northern Sweden.

Homozygous mutations in RLBP1 have also been found among patients in fundus albipunctatus (136880), retinitis punctata albescens, and in Newfoundland type retinal dystrophy (607476).

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

None has been reported. Tinted lenses can be helpful.

References
Article Title: 

Optic Nerve Edema, Splenomegaly, Cytopenias

Clinical Characteristics
Ocular Features: 

Persistent optic nerve edema is eventually followed by some degree of optic atrophy.  The nerve edema may be seen early in the first decade of life and is not associated with increased lumbar puncture pressure.  Peripapillary hemorrhages may be seen.  Visual acuity may decrease somewhat by the end of the first decade of life and becomes functionally significant in early adolescence and may be reduced to counting fingers.  The ERG, which shows minimal dysfunction early, eventually appears nearly flat without photopic or scotopic responses.  The retinal vessels become markedly attenuated and the macula may be mildly edematous and show pigmentary changes.  Pigment clumping is not seen.  Visual fields show a central or cecocentral scotoma, enlargement of the blind spot, and eventually severe peripheral constriction.  The vitreous and aqueous humor sometimes have an increased number of cells.   Lenticular opacities requiring cataract surgery has been reported.  One patient developed a phacomorphic angle closure attack at the age of 19 years.

Systemic Features: 

Splenomegaly is a consistent sign and is usually present in the first decade of life but histology shows primarily cellular congestion of the red pulp cords.  Bone marrow biopsies show mild erythroid hyperplasia. Peripheral blood counts show mild neutropenia and thrombocytopenia.  Occasional atypical lymphocytes may be seen.  Patients often complain of mildly to moderately severe migraine headaches.  Urticaria and anhidrosis are common features.

Genetics

Only a single report of this condition has been published.  A mother and two daughters (half sisters) had the symptoms described here and this is the basis for consideration of autosomal dominant inheritance.  Nothing is known regarding the etiology or the mechanism of disease.

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Topical, intravitreal, oral, and subtenon application of steroids apparently have no impact on the progression of the intraocular disease.  Cataracts may need to be removed.

References
Article Title: 

An inherited disorder with splenomegaly, cytopenias, and vision loss

Tantravahi SK, Williams LB, Digre KB, Creel DJ, Smock KJ, Deangelis MM, Clayton FC, Vitale AT, Rodgers GM. An inherited disorder with splenomegaly, cytopenias, and vision loss. Am J Med Genet A. 2012 Mar;158A(3):475-81. doi: 10.1002/ajmg.a.34437. Epub 2012 Feb 3.

PubMed ID: 
22307799

Spinocerebellar Ataxia 1

Clinical Characteristics
Ocular Features: 

Early manifestations include gaze-evoked nystagmus and saccadic hypermetria.  Ophthalmoplegia develops later in the disease process.  Some patients experience a decrease in acuity and dyschromatopsia.  The ERG shows evidence of generalized rod and cone photoreceptor dysfunction in some patients.  Optic atrophy, central scotomas, central RPE changes, retinal arteriolar attenuation, and blepharospasm have also been reported.

Time-domain OCT has revealed microscopic changes in the macula with thinning of the inner-outer segment junction and nuclear layer in areas with RPE hypopigmentation. 

Systemic Features: 

This is a progressive cerebellar syndrome characterized by systems of ataxia, dysarthria, and bulbar palsy.  Speech is often scanning and explosive.  DTRs can be exaggerated, and dysmetria is common.  The mean age of onset is about age 40.  Some cognitive decline may occur.  Muscle atrophy, and symptoms of peripheral neuropathy can be present.  MRI shows atrophy in the cerebellum, spinal cord, and brainstem.  There is considerable variation in clinical expression.  Individuals with adult onset of symptoms can survive for 10-30 years whereas those with a juvenile-onset often do not live beyond the age of 16 years.

Genetics

This disorder is caused by an expanded CAG repeat in the ataxin-1 gene (ATXN1) at 6p23.  It is an autosomal dominant disorder.  Alleles with 39-44 or more CAG repeats are likely to be associated with symptoms. 

A male bias and the phenomenon of anticipation have been demonstrated in this disorder as in spinocerebellar ataxia 7 (SCA7) (164500), in which affected offspring of males with SCA develop disease earlier and symptoms progress more rapidly than in offspring of females.  This is often explained by the fact that males generally transmit a larger number of CAG repeats.

SCA7 (164500), also inherited in an autosomal dominant pattern and caused by expanded CAG repeats on chromosome 3, has many similar ocular and neurologic features.

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Supportive care is often required.          

References
Article Title: 

Oculoauricular Syndrome

Clinical Characteristics
Ocular Features: 

This rare malformation syndrome affects primarily the eyes and ears.  The globes are small and usually have colobomas of both anterior and posterior segments.  The corneas likewise are small and often have opacities.  The anterior segment is dysplastic with anterior and/or posterior synechiae.  Glaucoma may be present.  The lenses may be small and often become cataractous.  There is a progressive rod-cone dystrophy associated with a pigmentary retinopathy.  Chorioretinal lacunae have been seen in the equatorial region.  The retinal degeneration is progressive, beginning with rod dysfunction but followed by deterioration of all receptors.  The onset in early childhood results in poor vision and nystagmus. 

Systemic Features: 

The external ears are abnormal.  The earlobes may have colobomas or may be aplastic.  The intertragic notch is often underdeveloped.  Audiograms and vestibular function tests, however, show normal function and MRI of the middle and inner ears likewise reveals no anatomic abnormalities.       

Among the few patients reported, dental anomalies, spina bifida oculta, and mild dyscrania have been noted in individual patients.

Genetics

This rare disorder has been reported in only a few families.  Based on parental consanguinity and homozygosity of mutations in the HMX1 gene (4p16.1) in affected sibs, this is an autosomal recessive disorder.  In one family there was a homozygous 26 bp deletion and in another a homozygous missense mutation.  The parents are heterozygous for the deletion.

HMX1 is a homeobox gene and the deletion abolishes its function by establishing a stop codon at position 112.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment is available for the extraocular malformations.  Glaucoma treatment and cataract surgery should be considered although permanent visual rehabilitation is unlikely given the progressive nature of the rod-cone dystrophy.

References
Article Title: 

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