Author: Guilherme Almeida (Portugal)
Co-authors: Francisco Alves, Miguel Leitão, Catarina Rodrigues, Cristina Santos, Luísa Santos
Achromatopsia (ACHM) is a rare inherited retinal disease, characterized by serious cone dysfunction, affecting approximately one in every 30,000 live births worldwide. Over 150 mutations in CNGA3 and CNGB3 genes have been identified as pathologic, accounting for approximately 70–80% of all cases of ACHM. The diagnosis is based upon clinical findings as reduced central visual acuity on early childhood, pathologic myopia, pendular nystagmus, photophobia, eccentric fixation with central scotomas and reduced or complete lack of colour vision (CV), suggested by signs of central macular atrophy on funduscopic examination, disruption of external segments of foveal photoreceptors on Optical Coherence Tomography (OCT), abnormal Colour Vision Testing (CVT), abnormal Visual Fields (VF) and abolished cone function on Eletrorretinography (ERG) and confirmed by genetic testing. The nature and early onset of sight impairment can be severely disabling, with significant impact on activities of daily living. We propose to describe 4 families with ACHM from our database, in order to raise awareness about this entity among Ophthalmologists.
Case Report from Ocular Genetics at Instituto de Oftalmologia Dr. Gama Pinto, Lisbon, Portugal
Research of ACHM cases from our Ocular Genetics database brought out 4 cases of different families that we decided to include in this report: Case 1: 29 years old female Case 2: 46 years old male Case 3: 9 years old male Case 4: 15 years old male
Case 1: Complaints of myopia, photophobia, nystagmus and colour vision deficiency (CVD) since childhood. Her parents shared consanguinity. Best Corrected Visual Acuity (BCVA) was 20 / 160 on both eyes (OU). Funduscopy showed orange-stained macula. VF revealed central escotomata and ERG photopic cone response was extinct. Genetic testing disclosed homozygous mutation in CNGB3. Case 2: Complaints of myopia, photophobia, nystagmus and CVD since 2. BCVA was 20 / 160 Right Eye (RE) and 20/200 Left Eye (LE). Funduscopy showed altered bilateral foveal reflex Funduscopy showed altered bilateral foveal reflex. VF revealed tunnel vision and ERG showed abolished photopic cone responses and diminished scotopic response. Genetic testing disclosed compound heterozygous mutation in CNGA3. Case 3: Complaints of myopia, photophobia, congenital nystagmus and severe CVD since 2. BCVA was 10/200 OU. Funduscopy showed altered bilateral foveal reflex. Genetic testing disclosed homozygous mutation in CNGB3. Case 4: Pakistanis, with myopia, photophobia, nystagmus and color blindness since birth. His parents are first cousins and his brother has similar vision problems. BCVA was 20 /160 RE and 20/200 LE. Funduscopy showed orange-stained macula and ERG showed abolished photopic cone responses and diminished scotopic response. Genetic testing disclosed homozygous mutation in CNGB3.
ACHM is a rare disease that progressively leads to serious loss of cones and consequently vision deficiency. It is inherited as an autossomic recessive pattern. A complete vision checkup is mandatory, including complementary exams as OCT, ERG, FAF, VF and CVT. Genetic counselling is recommended after genotyping. Novel mutations and pathologic variants are being constantly discovered, giving place for scientists and geneticists to develop innovative therapeutic genetic strategies.
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