Hereditary hypotrichosis of the Birman is a congenital disease of the hair follicle caused by a deletion in FOXN1. Affected kittens are born with very little hair or lose it early and do not develop a normal coat. Because FOXN1 is essential for thymus development, the hypotrichosis is accompanied by thymic aplasia and immunodeficiency, with poor development, recurrent respiratory and digestive infections and a markedly reduced life expectancy. It is inherited in an autosomal recessive manner.

Targeted at the Birman. In the French panel genotyped by Abitbol et al. (2015), the frequency of healthy carriers was estimated at 3.2%. There are no consolidated figures in other populations: limited data.

- Kittens born with little hair or bald in areas of the body\n- Sparse, thin coat with poor growth throughout life\n- Exposed skin with scaling, dermatitis and recurrent infections\n- Poor growth and development\n- High juvenile mortality and reduced life expectancy

Birman hypotrichosis was reported as a familial condition within the breed, with litters of hairless kittens or kittens with a very sparse coat that thrived poorly and died young. The pattern observed in affected litters was compatible with autosomal recessive inheritance, and the condition came to be included in Birman-specific DNA tests. The published molecular and clinical characterisation is limited: most of the available information comes from the laboratories offering the test. Any breeding decision should rely on the interpretation guidance of the test provider.

- Test Birman breeding animals: it distinguishes clear, carrier and affected.\n- Never mate two carriers together.\n- A carrier can be mated to a clear animal with no risk of affected kittens; test the offspring that remain in breeding.\n- Do not use affected cats for breeding, and meet their dermatological needs under veterinary supervision.

The phenotype is due to a deletion in FOXN1, a transcription factor key to thymus and hair follicle development; therefore affected kittens present hypotrichosis together with thymic aplasia/dysplasia and immunodeficiency, the main cause of the infections that lead to early death. Differential diagnosis with other congenital alopecias (follicular defects, dermatophytosis in kittens, demodicosis, nutritional alopecias) and with the recessive sparse feline coat of other breeds. Skin biopsy helps characterise individual cases. Hypotrichotic cats require thermal and skin protection, control of secondary infections and monitoring of weight gain.

1. Abitbol M, Bossé P, Thomas A, Tiret L. A deletion in FOXN1 is associated with a syndrome characterized by congenital hypotrichosis and short life expectancy in Birman cats. PLoS One 2015. PMID:25781316.
2. Lyons LA. DNA mutations of the cat: the good, the bad and the ugly. J Feline Med Surg 2015. PMID:25701860.
3. OMIA:001949-9685 Hypotrichosis, with thymic aplasia (Felis catus).