When genetic tests threaten the gene pool

2014: A test result becomes a breeding concern

On 11 October 2014, approximately 25 people attended a meeting about MPS in Korsør, Denmark. The minutes recorded results for 57 Sacred Birmans: 20 tested normal, 28 carried one copy of the then “mild” variant and nine had two copies. The latter group was described by the testing terminology of the time as “affected”.

Yet the same minutes stated that no clinical signs of the “mild” form were known at that point. This does not prove all cats were healthy; it illustrates how a laboratory classification can be mistaken for a confirmed clinical diagnosis. Participants also worried that removing many breeding cats could increase inbreeding and reliance on a small number of popular sires.

2016: The researchers clarify what the test means

In 2016, Lyons and colleagues published a peer-reviewed clarification of feline MPS VI testing. The severe disease-associated ARSB variant is L476P (c.1427T>C). By contrast, the more common D520N (c.1558G>A), previously described as “mild MPS VI”, showed no evidence of association with disease when present alone.

The authors specifically discussed the Sacred Birman: genetic diversity was already reduced and D520N occurred frequently. Selecting against D520N alone was not warranted and could narrow the gene pool unnecessarily. This does not mean that severe MPS VI does not exist.

2022: A modifier is not a diagnosis

A genetic survey of more than 11,000 cats designated D520N as an “MPS VI Modifier”. It can influence disease in combination with the severe L476P variant, for example when one copy of each is inherited. D520N alone does not justify eliminating breeding lines.

MPS VI prevention therefore requires attention to the actual pathogenic variant, relevant combinations and veterinary assessment, not merely a highlighted result in a large commercial DNA panel.

2024: More tests are not necessarily better

In a veterinary review, Leslie A. Lyons warned that large genetic panels can be misinterpreted. Before neutering a cat or removing it from a breeding programme on DNA evidence alone, appropriate genetic and veterinary advice should be sought and the diversity of the entire population considered.

Responsible breeding also considers clinical health, family history, temperament, function, fertility and the risks of concentrating breeding on a handful of animals.

What breeders should do

Use targeted, reliable testing for variants with a documented disease relationship where clinically relevant. Check exactly which variant a report detects, and whether the laboratory label refers to a genotype or established clinical disease.

Retain valuable, healthy breeding animals where safe mating choices and an evidence-based plan are available. For severe recessive disorders, avoid affected offspring while preserving genetic diversity wherever possible. Suspected illness must always be assessed by a veterinarian.

The goal is not the greatest possible number of negative DNA results. The goal is healthy, functional Sacred Birmans for generations to come.