Tag Archive for FGF5

Controversial DNA test results?

There was recently a huge discussion about the test results for an “Aby” whose DNA sample has been sent to two labs (UC Davis and Texas A & M) for screening if the cat carries for longhair since only 10 years ago some Somalis were introduced in that pedigree. The results came back different or should I say inconclusive. Read my thoughts about it below.

I will be trying to explain with different words and  how the explanatory text from the Texas A&M site can be interpreted and whose correct link, btw, is:
http://www.catdnatest.org/DNA-results.html .

First thing to notice is, that apparently Texas A&M (other than UC Davis) only tests for 3 of the 4 Mutations involved in modifying hair length in cats. They are M1, M2 and M4, hence they do not test for M3. Also the Texas A & M uses two different markers for M4 (M4 and M4_2), due to difficulties in typing they say. Their observance in results is, that in most cases the result is the same for both markers (for example M4 +/- and M4_2 +/-). In order for a cat to show the longhair however it seems that cats need to have two mutations at either M4 or M4_2 (or both together?). One mutation at each marker of M4 would not make it a longhair cat, unless there would be an additional mutation at one of the other loci (M1- M3). So the compound heterozygote doesn’t apply for mutation M4 when both markers have one mutation.

Below you can see a couple of combinations of different mutations and how they “translate”:

Mutation M1 Mutation M2 Mutation M3 Mutation M4 Mutation M4_2 Phenotype Genotype
+/- +/- -/- -/- -/- longhair compound heterozygote
-/- -/- +/- +/- -/- longhair compound heterozygote
-/- -/- -/- +/+ -/- longhair homozygote
-/- -/- +/- -/- -/- shorthair carrying M3
-/- -/- -/- +/- +/- shorthair carrying M4/M4_2
-/- -/- -/- -/- -/- shorthair homozygote
-/- -/- +/- +/- -/- longhair compound heterozygote

The test result for the cat in questions shows one mutation for M4_2, and no mutation for M4. Cat also doesn’t have any mutation for M1 and M2, M3 is not tested by that Laboratory. Another Laboratory reported the cat to be free of any mutation (M1-M4), but I do not know wether they test for both markers in M4.  So far, it is not clear, whether mutation M4_2 is functional or not. None of the description I read so far did state that anywhere clearly, neither pro nor con. If there do exist cats which tested M4_2 +/+ and are phenotypically longhaired, then the answer should be yes. Question is, did they also test M4 +/+, if so, it still would not be clear if the mutation M4 at the 2nd marker is functional or not. My first approach would be to contact Texas A&M and ask them exactly that question. Maybe, they are inconclusive themselves, then we are back to square.

Another thought we never have to dismiss when receiving test results for genetic screening is: Possibilities for errors due to contamination (during or after sampling) or other causes DO exist. Read more about at the following site: DNA Testing: An Introduction for Non-Scientists If nothing else then I would at least resample the cat in question by trying to be as careful as possible to avoid contamination during sampling. Then sending the NEW sample to both Laboratories, maybe even a third, and see how the results translate. This can become quite costly and the question arises if it would not be simpler to just mate the cat in question to a longhair cat and see whether it produces longhair offspring. Unfortunately, even if one phenotypically HAS the trait and the other one carries it, there is not 100% certainty that the recessive will show in offspring in just one mating. On the other hand, why even going through all these obstacles from multiple testing to possible test matings if the pedigree shows recent introduction of the longhair? Our breed still has a large genepool if breeders take the time and work to search for outcrosses not having another breed recently introduced.

Other than all of the above said and if the mutation M4 at the 2nd marker IS functional then of course the cat CAN produce longhaired offspring.

In addition we still do not know if more mutations exist that could affect growth of hair. Quoting from the study: “Although this study included 62 unrelated individuals from 14 long-haired breed registries and 23 long-haired nonbreed cats from the Johns Hopkins University and Nestle-Purina pedigrees, it is possible that additional mutations in the feline FGF5 gene may be present in unsampled long-haired breed and nonbreed cats. In addition, the reported quantitative and qualitative differences between the coats of long-haired cat breeds indicate that other independent loci may modify the major influence of FGF5 on hair length in the domestic cat (Vella and Robinson 1999).”

The fulltext study can be found here, or read the abstract of the other study.


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