Test Detail

Frontonasal dysplasia (Burmese)

Musculoesquelético · Cat

Hereditary frontonasal dysplasia of the Burmese cat, caused by a 12-bp in-frame deletion in ALX1. The allele is co-dominant: heterozygotes show the brachycephalic 'Contemporary Burmese' phenotype, whereas homozygotes suffer a severe craniofacial defect (agenesis of derivatives of the medial nasal prominence, meningoencephalocele and ocular degeneration) incompatible with life.

Inheritance pattern	Autosomal co-dominant. Heterozygotes show brachycephaly (selected trait) and homozygotes present lethal frontonasal dysplasia. 25 % of the offspring of matings between heterozygotes are affected homozygotes.
Gene / Mutation	ALX1 12-bp in-frame deletion: c.497_508del p.(A166_T169del) (current nomenclature; published as c.496delCTCTCAGGACTG); F.catus_Fca126_mat1.0 (NC_058374.1) g.107855022_107855033del, feline chromosome B4; OMIA002717-9685. It removes 12 nucleotides without altering the reading frame and is consistently associated in 100 % with the craniofacial defect of the Contemporary Burmese (gene on chromosome B4).
Penetrance	The allele shows complete, dose-dependent expression: homozygotes develop the severe craniofacial defect and heterozygotes the characteristic brachycephaly. There are no silent carriers: brachycephaly is the manifestation of the heterozygous state.
Code	hrib
Turnaround time	15 days
Price	52,60 €

Incidence

Documented in the Burmese cat ('Contemporary Burmese' line). The variant was not found in cats unrelated to that line. Broad population frequencies are not available (limited data).

Breeder management

- A genetic test is available for ALX1 c.497_508del.\n- Do not mate two heterozygotes: 25 % of the offspring would be homozygous and lethal.\n- Bear in mind that the allele is the trait of the Contemporary line, so selection depends on the degree of brachycephaly desired.\n- Pairing heterozygotes only with clear homozygotes avoids litters with lethal affected kittens.\n- Document the genetic status of the breeding animals.

Specialist notes

The variant is co-dominant and lethal in homozygosity; affected kittens are born alive with a severe facial defect and meningoencephalocele, and euthanasia is indicated. Prevention is based on genotyping breeding animals. Do not confuse the normal brachycephaly of the breed with homozygous frontonasal dysplasia.

References

1. Lyons LA et al. 2016. Aristaless-Like Homeobox protein 1 (ALX1) variant associated with craniofacial structure and frontonasal dysplasia in Burmese cats. Developmental Biology. PMID: 26610632
2. OMIA:002717-9685. Frontonasal dysplasia, ALX1-related in Felis catus. Online Mendelian Inheritance in Animals.

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