Multi-disease genetic panel for the Chinese Crested grouping six molecular tests for hereditary conditions described in the breed: two forms of progressive retinal atrophy (prcd-PRA and rcd3-PRA), canine multiple system degeneration (CMSD), neuronal ceroid lipofuscinosis (NCL), primary lens luxation (PLL) and degenerative myelopathy (DM exon 2). Each test reports clear/carrier/affected status for the corresponding variant and allows matings to be planned while avoiding diseased animals. The panel does not replace ocular examination or neurological follow-up: several conditions are late-onset or of variable penetrance, and molecular testing is only one part of reproductive management.

Applicable breed: Chinese Crested. The rcd3 variant (PDE6A) is documented in the Chinese Crested (Downs et al., 2014), CMSD is a rare disease specific to the Chinese Crested and the Kerry Blue Terrier, and NCL7 (MFSD8) was initially described in the Chinese Crested. There are no published estimates of carrier frequency in the breeding population for the six variants (limited data).

- Reduced night vision and progressive retinal atrophy (prcd-PRA and rcd3-PRA)\n- Progressive blindness with altered fundus; rcd3-PRA has an earlier onset\n- Progressive ataxia, behavioural deterioration and multiple neurological signs from a young age (CMSD, NCL)\n- Lens luxation with painful red eye, mydriasis and secondary glaucoma (PLL)\n- Progressive hindlimb paresis with proprioceptive ataxia (DM)

The tests in the panel were developed independently. prcd-PRA was associated with the PRCD gene (Zangerl et al., 2006). rcd3-PRA was associated with a mutation in PDE6A, described in the Cardigan Welsh Corgi (Petersen-Jones et al., 1999) and later documented in the Chinese Crested and the Pomeranian by panel screening (Downs et al., 2014). CMSD was first described in the Kerry Blue Terrier and in 2024 was associated with biallelic variants of SERAC1, with a deletion in the splice acceptor of exon 4 specific to the Chinese Crested (Zeng et al., 2024). NCL in the Chinese Crested was associated with a 1-bp deletion in MFSD8 (CLN7; NCL7) (Guo et al., 2015). PLL was associated with ADAMTS17 with autosomal recessive inheritance (Farias et al., 2010; OMIA:000588-9615). Canine DM was linked to the SOD1 exon 2 variant (Awano et al., 2009).

- Genotype breeding animals before mating; the panel covers six conditions in a single sample\n- For all the conditions (autosomal recessive: prcd-PRA, rcd3-PRA, CMSD, NCL, PLL, DM): do not mate two carriers — 25 % risk of homozygotes; carrier × clear is safe for offspring intended for breeding if tested\n- For PLL: prioritise clear animals for breeding lines and maintain annual ophthalmological examination, since penetrance is incomplete\n- For DM: remember the incomplete penetrance; homozygotes are not a breeding priority\n- After a confirmed clinical case, do not repeat the parental mating and communicate the status to the buyer

Check the exact panel offered by each laboratory, because not all include the six variants for the Chinese Crested. Annual ocular examination (ECVO/CERF) is complementary. rcd3 (PDE6A) and rcd1 (PDE6B) affect different subunits of the same enzyme; confirmation requires the specific PDE6A test. PLL is autosomal recessive (OMIA:000588-9615) and must be differentiated from traumatic luxation or luxation secondary to uveitis. CMSD and NCL require histopathological or immunohistochemical confirmation. DM is a diagnosis of exclusion: rule out spinal cord compression, disc herniation and neoplasia before attributing the picture to SOD1.

1. Petersen-Jones SM, et al. cGMP phosphodiesterase-alpha mutation causes progressive retinal atrophy in the Cardigan Welsh corgi dog. Invest Ophthalmol Vis Sci. 1999. PMID: 10393029.
2. Zangerl B, et al. Genomics. 2006. PMID: 16938425.
3. Downs LM, et al. Genetic screening for PRA-associated mutations in multiple dog breeds shows that PRA is heterogeneous within and between breeds. Vet Ophthalmol. 2014. PMID: 24255994.
4. Zeng R, et al. Canine multiple system degeneration associated with sequence variants in SERAC1. Genes (Basel). 2024. PMID: 39596578.
5. Guo J, et al. A rare homozygous MFSD8 single-base-pair deletion and frameshift in a Chinese Crested dog with neuronal ceroid lipofuscinosis. BMC Vet Res. 2015. PMID: 25551667.
6. Farias FH, et al. An ADAMTS17 splice donor site mutation in dogs with primary lens luxation. Invest Ophthalmol Vis Sci. 2010. PMID: 20375329.
7. Awano T, et al. PNAS. 2009. PMID: 19188595.
OMIA:001314-9615 (rcd3/PDE6A); OMIA:001468-9615 (CMSD/SERAC1); OMIA:001962-9615 (NCL7/MFSD8); OMIA:000588-9615 (PLL).