Test Detail

Achromatopsia (Day blindness) (ACHM)

Ocular · Dog

Hereditary dystrophy of cone photoreceptors that causes day blindness (hemeralopia) and photophobia with preserved night vision. Affected dogs show poor vision in bright light and light-avoidance behaviour. It is the canine equivalent of human achromatopsia. It has been described in the German Shepherd and Labrador Retriever (CNGA3 variants, ACHM2 form) and in the Alaskan Malamute and Miniature Australian Shepherd (CNGB3 variant, ACHM3 form).

Inheritance pattern	Autosomal recessive
Gene / Mutation	CNGA3 (OMIA001481-9615) and CNGB3 (OMIA001365-9615) genes. German Shepherd: CNGA3 NC_006592.3:g.44234861G>A / c.1270C>T / p.(R424W) (OMIA Variant 97; PMID 26407004). Labrador Retriever: CNGA3 NC_006592.3:g.44234198_44234200del / c.1931_1933del / p.(V644del) (OMIA Variant 548; PMID 26407004). Alaskan Malamute and Miniature Australian Shepherd (ACHM3, CNGB3): deletion removing all CNGB3 exons (OMIA Variant 631; PMID 12140185, 23601474). The test is variant- and gene-specific.
Penetrance	High penetrance in homozygotes for the known CNGA3 variants (German Shepherd and Labrador) and CNGB3 variants (Malamute and Miniature Australian Shepherd); heterozygotes are phenotypically normal.
Code	bict
Turnaround time	15 days
Price	52,60 €

Incidence

Limited data. Cases described in specific lines of German Shepherd, Alaskan Malamute and Labrador Retriever; no reliable population frequencies have been published. The Malamute form (ACHM2/CNGB3) is better characterised.

Breeder management

- Screen breeding animals of affected breeds before mating when a molecular test specific for the breed's variant is available (CNGA3 in German Shepherd, CNGB3 in Malamute)\n- Do not mate two identified carriers\n- In the absence of a test, avoid repeating matings that have produced affected puppies\n- Confirm the diagnosis with a full ERG (separate assessment of cones and rods) and fundus examination

Specialist notes

ERG with a cone (photopic) and rod (scotopic) protocol is the key element of diagnosis: achromatopsia shows a cone defect with preserved rod function. Differentiate it from progressive retinal dystrophies (PRA) that affect both types of photoreceptors and from cortical blindness. The molecular test is variant-specific: the CNGB3 test (Malamute) does not cover the German Shepherd CNGA3 variant and vice versa.

References

1. Sidjanin DJ et al. (2002) Canine CNGB3 mutations establish cone degeneration as orthologous to the human achromatopsia locus ACHM3. Hum Mol Genet 11:1823-1833. PMID: 12140185
2. Tanaka N et al. (2015) Canine CNGA3 gene mutations provide novel insights into human achromatopsia-associated channelopathies and treatment. PLoS One 10:e0138943. PMID: 26407004
3. Yeh CY et al. (2013) Genomic deletion of CNGB3 is identical by descent in multiple canine breeds and causes achromatopsia. BMC Genet 14:27. PMID: 23601474
4. OMIA:001481-9615 (Achromatopsia-2, CNGA3-related) y OMIA:001365-9615 (Achromatopsia-3, CNGB3-related).

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