ACO2

Infantile Cerebellar-Retinal Degeneration

Clinical Characteristics
Ocular Features: 

Visual tracking can be normal during the newborn period but lack of visual fixation and attention soon become evident.  Strabismus, nystagmus, and abnormal pursuit movements are often present.  Optic atrophy has been reported as early as 3 years of age.  VEP and ERG responses are extinguished in the first two years. The nystagmus may be multidirectional.  Acuity loss seems to be progressive.  A progressive retinal degeneration (not further characterized) has been reported.

Systemic Features: 

Infants generally appear normal at birth.  Within the first 6 months they show signs of developmental delay and neurological signs such as truncal hypotonia, seizures, athetosis and head bobbing.  Milestones of sitting, rolling over, and reactions to others are seldom achieved.  Cerebellar brain imaging shows progressive atrophy in all patients and some have cortical atrophy as well.  Some patients have evidence of hearing loss.   Severe failure to thrive and psychomotor delays are usually present.  Death may occur within several months of birth although some live for several decades.

Genetics

This condition results from homozygous or compound heterozygous mutations in the ACO2 gene (22q13.2).  The mutation has also been associated with optic atrophy 9 (616289).

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment beyond supportive care is known.

References
Article Title: 

Mutations in the tricarboxylic acid cycle enzyme, aconitase 2, cause either isolated or syndromic optic neuropathy with encephalopathy and cerebellar atrophy

Metodiev MD, Gerber S, Hubert L, Delahodde A, Chretien D, Gerard X, Amati-Bonneau P, Giacomotto MC, Boddaert N, Kaminska A, Desguerre I, Amiel J, Rio M, Kaplan J, Munnich A, Rotig A, Rozet JM, Besmond C. Mutations in the tricarboxylic acid cycle enzyme, aconitase 2, cause either isolated or syndromic optic neuropathy with encephalopathy and cerebellar atrophy. J Med Genet. 2014 Dec;51(12):834-8.

PubMed ID: 
25351951

Optic Atrophy 9

Clinical Characteristics
Ocular Features: 

Two brothers have been reported with optic atrophy discovered as early as 3 and 5 years of age.  Visual acuity in the 3rd decade of life was in the 20/200 range which was stable into the 4th and 5th decades. They also had red-green dyschromatopsia and thinning of the nerve fiber layer most pronounced in the temporal areas of the retina corresponding to the location of most marked pallor seen in the optic nerve.  The nasal nerve fiber layer seemed to be preserved.  Paracentral scotomas could be demonstrated. 

Systemic Features: 

There were no systemic abnormalities reported in the brothers. 

Genetics

OPA9 is caused by homozygous or compound heterozygous mutations in the ACO2 gene (22q13.2).   

Mutations in ACO2 also cause infantile cerebellar retinal degeneration (ICRD) (614559) in which optic atrophy is a prominent feature associated with retinal degeneration, extensive neurodegenerative disease, and mitral valve dysfunction.  The mode of inheritance is autosomal recessive.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment has been described.

References
Article Title: 

Mutations in the tricarboxylic acid cycle enzyme, aconitase 2, cause either isolated or syndromic optic neuropathy with encephalopathy and cerebellar atrophy

Metodiev MD, Gerber S, Hubert L, Delahodde A, Chretien D, Gerard X, Amati-Bonneau P, Giacomotto MC, Boddaert N, Kaminska A, Desguerre I, Amiel J, Rio M, Kaplan J, Munnich A, Rotig A, Rozet JM, Besmond C. Mutations in the tricarboxylic acid cycle enzyme, aconitase 2, cause either isolated or syndromic optic neuropathy with encephalopathy and cerebellar atrophy. J Med Genet. 2014 Dec;51(12):834-8.

PubMed ID: 
25351951
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