Panel for the Arabian horse that brings together the three tests for its components: equine cerebellar abiotrophy (CA), lavender foal syndrome (LFS) and severe combined immunodeficiency (SCID). All three are autosomal recessive diseases with healthy heterozygotes, so DNA testing is the only way to identify carriers. LFS and SCID are lethal in homozygosity; CA has no treatment and limits the functionality of the affected animal.

Applicable breed: Arabian and its crosses. CA: sporadic but recurrent in the Arabian; carrier prevalence of 5.1% (95% CI 2.5-9.1) in South African Arabians (Tarr et al., 2014); exceptional outside the Arabian. LFS: concentrated in the Arabian, with greater presence in lines of Egyptian ancestry; there is no universal frequency (Gabreski et al., 2012; AbouEl Ela et al., 2023). SCID: Tarr et al. (2014) described in South African Arabians a carrier prevalence that fell from 6.4% (2004/5 season) to 3.4% (2009/10) after introducing the test.

- Cerebellar ataxia with wide base, hypermetria, intention tremor and signs visible between 6 and 16 weeks of life, without recovery from the deficit (CA)\n- Grey-lavender coat dilution at birth, tetany, seizures, opisthotonus and inability to stand and suckle; death or euthanasia in the first days (LFS)\n- Recurrent and severe infections from 2-8 weeks of life (diarrhoea, pneumonia), marked lymphopenia and absence of own IgM; death in the first months (SCID)

CA has been known in the Arabian for decades; Brault et al. (2011) mapped it to ECA2 and described a candidate variant in TOE1/MUTYH. LFS was described in Arabian lines, with greater presence in Egyptian ancestry; Brooks et al. (2010) identified the causal deletion in MYO5A. Arabian foal SCID was described in the 1970s (McGuire and Poppie, 1973) and in the 1990s it was shown that the defect lies in V(D)J recombination and DNA-PK, with mutations in PRKDC (Wiler et al., 1995; Shin et al., 1997).

- Test Arabian breeding animals before the first breeding season, as a priority in lines with Egyptian ancestry\n- Never mate carrier x carrier: 25% risk of affected foals in each breeding for the three diseases\n- A carrier can be mated to a clear individual, keeping only clear offspring for breeding if the goal is to eliminate the allele\n- Affected animals should not be used in breeding or as athletes\n- The birth of a lavender foal or one with recurrent infections makes it mandatory to test the parents and not repeat the mating; record the results in the breeders' association

The differential diagnosis of CA includes traumatic or compressive cervical ataxia, meningoencephalitis (for example, EPM in endemic areas), intoxications and LFS; definitive confirmation is neuropathological (loss of Purkinje cells). The neonatal differential diagnosis of LFS includes neonatal maladjustment syndrome, hypoxic-ischaemic encephalopathy and sepsis; the coat dilution is the guiding clue. In SCID, rule out failure of passive transfer of immunity (serum IgG in the first 24 hours); it is confirmed by lymphopenia, absence of IgM and genetic testing of the foal and its parents. The CA test is based on a candidate variant and should be interpreted together with the pedigree and the phenotype.

Componente CA (eemy):
1. Brault LS et al. 2011. Mapping of equine cerebellar abiotrophy to ECA2 and identification of a potential causative mutation affecting expression of MUTYH. Genomics. PMID: 21126570
2. Tarr CJ et al. 2014. The carrier prevalence of severe combined immunodeficiency, lavender foal syndrome and cerebellar abiotrophy in Arabian horses in South Africa. Equine Vet J. PMID: 24033554
3. Scott EY et al. 2018. Variation in MUTYH expression in Arabian horses with cerebellar abiotrophy. Brain Res. PMID: 29103988
4. OMIA:000175-9796. Cerebellar abiotrophy.

Componente LFS (szxa):
5. Brooks SA et al. 2010. Whole-genome SNP association in the horse: identification of a deletion in myosin Va responsible for Lavender Foal Syndrome. PLoS Genet. PMID: 20419149
6. Gabreski NA et al. 2012. Investigation of allele frequencies for Lavender foal syndrome in the horse. Anim Genet. PMID: 22497275
7. AbouEl Ela NH et al. 2023. Evidence for origin of lavender foal syndrome among Egyptian Arabian horses in Egypt. Equine Vet J. PMID: 35665534
8. Christen M et al. 2021. MYO5A frameshift variant in a miniature Dachshund with coat color dilution and neurological defects resembling human Griscelli syndrome type 1. Genes (Basel). PMID: 34680875
9. OMIA:001501-9796. Dilute coat color with neurological defects.

Componente SCID (jkql):
10. McGuire TC, Poppie MJ. 1973. Hypogammaglobulinemia and thymic hypoplasia in horses: a primary combined immunodeficiency disorder. Infect Immun. PMID: 4199158
11. Wiler R et al. 1995. Equine severe combined immunodeficiency: a defect in V(D)J recombination and DNA-dependent protein kinase activity. Proc Natl Acad Sci U S A. PMID: 8524788
12. Shin EK et al. 1997. A kinase-negative mutation of DNA-PK(CS) in equine SCID results in defective coding and signal joint formation. J Immunol. PMID: 9103416
13. Tarr CJ et al. 2014. The carrier prevalence of severe combined immunodeficiency, lavender foal syndrome and cerebellar abiotrophy in Arabian horses in South Africa. Equine Vet J. PMID: 24033554
14. OMIA:000220-9796. Severe combined immunodeficiency disease, autosomal, PRKDC-related.