Unraveling the Mystery Behind Cat Combo SM. What It Means and Why It Matters

What Does ‘SM’ Mean for Cat Colors?

The letters ‘SM’ in cat genetics refer to a gene mutation that causes a dilute or washed-out version of the base coat color. The specific gene affected is the Melanophilin gene (MLPH), which helps regulate the distribution of pigment in hair follicles.

The SM gene mutation results in less pigment overall in the coat, creating a “diluted” or paler version of the cat’s base color. For example, a black cat with the SM mutation would have a gray or “blue” coat. The mutation affects the synthesis and distribution of both eumelanin (black/brown pigment) and pheomelanin (red/yellow pigment) in the hair shafts.

The SM gene mutation is incompletely dominant, meaning a cat only needs one copy of the mutated gene to exhibit the dilute coat colors. Kittens that inherit two copies of the SM gene (homozygous) tend to have extremely pale, almost white coats.

In genetic terminology, cats with the SM gene mutation are referred to as “silver” or “smoke” cats. The mutation causes a range of diluted color patterns depending on the cat’s base coat color. This includes blue, lilac, fawn, cream, silver tabby, smoke, and more.

Source: https://catspurfection.com/silver-and-smoke-cats/

Origins of the SM Gene Mutation

The SM gene mutation first occurred randomly in domestic cats, although the exact origin is unknown. According to Cat Genetics, an online cat genetics resource, the mutation likely arose spontaneously in a domestic cat population sometime in the early 20th century (Cat Genetics, 2022).

The gene mutation causes a variance in the distribution of melanin pigment in cats with the dominant tabby coat pattern (Menotti-Raymond et al., 2009[1]). This results in diluted coloration, including lighter pigment in the fur and nose leather. The name “SM” stands for “silver modification,” referring to its effect on changing normal tabby coat colors.

Although the mutation arose randomly, breeders took interest in the unique SM cat coat patterns that emerged and began intentionally breeding cats to select for the trait. This allowed the gene mutation to spread through cat breeding populations and become established in certain pedigreed breeds, such as the Chinchilla Persian.

How the SM Gene Works

The SM gene causes a mutation that restricts the production of melanin pigment to just the tips of the cat’s hair shaft (https://thelittlecarnivore.com/en/blog/cat-coat-silver-and-smoke-cats). Melanin is what gives color to a cat’s fur. Typically, melanin is distributed evenly throughout each hair strand from root to tip. But in cats with the SM gene mutation, melanin production is inhibited so that color is only present at the very tips of the fur.

This results in a “frosting” effect, with the hair tips appearing darker while the base of the hair shaft stays white or silver. It creates a faded or diluted appearance compared to non-silver fur colors. The degree of fading varies based on whether a cat has one or two copies of the SM gene.

Cat Breeds with the SM Gene

Several cat breeds commonly exhibit the silver tabby pattern and smoke coat colors associated with the SM gene mutation. Some of the most well-known include:

Silver Persians – One of the most popular cat breeds, Persians were among the first to display the silver tabby pattern. The silver Persian combines the long-haired Persian look with a light silver base coat over tabby striping.

British Shorthairs – Known for their rounded faces and dense coats, British Shorthairs also come in a range of silver tabby patterns, from classic to mackerel. The silver British Shorthair has an icy sheen.

Norwegian Forest Cats – These large, long-haired cats make great companions. With their thick ‘waterproof’ coat, Norwegian Forest Cats in silver tabby can handle cold winters in style.

Silver Tabby Cat Patterns

Silver cats with the SM gene can display a variety of tabby patterns in their fur. Some of the most common tabby patterns seen in silver cats include:

  • Classic Tabby: This features bold stripes that run in a vertical pattern along the cat’s sides. The stripes are thicker along the spine and break into swirls and spots along the cat’s belly and legs.
  • Mackerel Tabby: With this pattern, narrow vertical lines run along the cat’s sides in a fishbone or mackerel-like pattern. The stripes may continue in a circular pattern around the legs.
  • Spotted Tabby: In this pattern, the stripes break into spots. The spots can vary in size and shape. Often the spots become smaller and denser along the legs and face.
  • Ticked Tabby: This causes the fur to have a salt-and-pepper sprinkled look. The tabby markings are visible when the cat is a kitten but fade as the cat matures.

There are also some rarer tabby patterns sometimes seen in silver cats, like the patched tabby which features a mix of stripes and swirled blotches or the marbled tabby which has swirled lines instead of straight stripes. The specific tabby pattern displayed can depend on the cat’s breed and genetics.

For images and examples of tabby patterns in silver cats, check out this guide: https://silvershorthairs.com/2017/09/23/featured-content/

Smoke Cat Colors

Smoke cat coloring has a unique appearance that looks like wispy swirls of smoke. This effect is created by the cat having colored hair tips, while the roots of the hair shaft are white or silver. When the cat’s fur is parted, the white roots are visible underneath the overcoat of colored tips. As the cats shed and new hairs grow in, the smoke effect becomes more pronounced as more white roots are exposed. The overall impression is of a cat whose coat color seems to drift and swirl like smoke.

According to an article on The Little Carnivore, “A smoke cat, instead of having fully-colored hairs, only has the tips of its hairs which are colored, while the roots are white.”[1] The smoke coloring can manifest in several cat coat colors, including black, blue, red, cream and tortoiseshell. Kittens may not show their full smoke patterns until they mature.

As described in an article on Cats.com, “The smoke cat color pattern is a solid color that’s white at the roots, which causes a unique effect reminiscent of swirling smoke.”[2] The fur gives the visual effect of smoke swirling within the cat’s coat. This unusual coloring results from the silvering gene mutation known as SM, which causes the color to be diluted at the roots.


[1] https://thelittlecarnivore.com/en/blog/cat-coat-silver-and-smoke-cats

[2] https://cats.com/rare-coat-colors-in-cats

Caring for Cats with the SM Gene

Cats with the silver/smoke gene require similar care as other cats, but there are a few special grooming and health considerations to be aware of.

Grooming tips for silver and smoke cats include:

  • Use a stainless steel comb to work through tangles and remove loose fur. The SM gene can cause more shedding. Regular combing keeps the coat tidy.
  • Bathe cats sparingly, only when necessary. Over-bathing strips oils and leads to dry, brittle fur in silver/smoke cats.
  • Trim nails every 2-3 weeks to maintain healthy paws. The SM gene can cause nails to be thicker.
  • Wipe facial folds daily on flat-faced breeds like Persians to prevent tear-staining.
  • Brush teeth weekly to control plaque buildup which shows up more visibly on silver coats.

On the health side, research by The Little Carnivore found the SM gene may increase susceptibility to:

  • Dental issues
  • Skin and coat problems
  • Eye conditions like cherry eye

So regular vet checkups to monitor for these conditions is recommended. With proper care and grooming, silver and smoke cats can stay healthy and maintain their eye-catching coats.

Impact on Cat Shows and Breeding

The silver gene mutation has had a significant impact on the cat show world and for cat breeders. Many cat breed standards exclude silver colored cats or have special restrictions around showing silver colored cats from breeds that are not typically silver.

For example, The Cat Fanciers’ Association (CFA) has created special color classes for silver colored cats in breeds that are not typically seen in the dilute colors. This includes colors like “blue” (gray), fawn (light brown), and cream (pale buff) that result from the silver gene. So a silver colored Russian Blue would compete in a special color class separate from the traditional blue Russian Blues.

These special color classes create complications for cat breeders who want to work with the dilute colors. The small class sizes due to fewer eligible cats makes it more difficult for silver colored cats to earn titles and awards. This has discouraged some breeders from working with the dilute colors, even if they find the silver patterns appealing.

There is also difficulty in meeting the breed standard perfectly with the diluted pigment. A silver cat may not have the vibrant, rich color desired for the breed. For example, a silver Maine Coon may not have the deep, warm brown color specified in the standard. This can count against the cat during judging. So the silver gene presents challenges for breeders to meet the ideal look defined in their breed’s standard.

Other Dilute Cat Colors

In addition to silver and smoke, there are other dilute cat coat colors that involve the same SM gene mutation. These include:

Blue – This is a dilution of black pigment, resulting in a grayish or silvery blue coat. The SM gene causes partial melanin pigment expression, turning black fur into blue. Breeds with a blue coat include Russian Blue, British Shorthair, and Chartreux. Source

Cream – This dilute version of red or ginger cat fur results in a pale buff or cream color. The cream gene blocks some reddish pigment from developing. Breeds with cream coats include Devon Rex, Cornish Rex, and Turkish Van. Source

Cinnamon – This is a dilute version of chocolate or brown fur in cats. The SM gene reduces brown pigment, creating a tan, fawn, or cinnamon hue. This color is seen in breeds like the Havana Brown and Oriental Shorthair. Source

Frequently Asked Questions

Here are some common questions about silver and smoke cats:

What breeds can have the silver/smoke coat?

Many breeds can display the silver/smoke coat effect including Persian, Exotic Shorthair, British Shorthair, Oriental, Siamese, and Russian Blue cats.

Do silver/smoke cats shed more than other cats?

No, the silver/smoke coat gene does not affect shedding. All cats shed to some degree. The amount of shedding depends more on the length of the fur rather than the color. Short-haired silver tabby cats will shed a similar amount to other shorthairs.

Are silver/smoke cats rare?

While not as common as some other colors, silver/smoke coats are not considered rare. Their unique appearance does make them popular among cat fanciers and breeders.

Do silver/smoke cats have health problems?

There are no known health problems specifically associated with the silver/smoke gene. Like all cats, silver/smoke cats can be prone to certain breed-related conditions.

Do silver/smoke cats have different personalities?

There is no evidence that coat color is linked to personality in cats. Silver/smoke cats have unique looks but their temperaments vary individually just like cats of any other color.

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