The Norwegian Forest cat (Norsk skogskatt and Norsk skaukatt) is a breed of domestic cat originating in Northern Europe. This natural breed is adapted to a very cold climate, with a top coat of long, glossy hair and a woolly undercoat for insulation. The breed's ancestors may have been a landrace of short-haired cats brought to Norway about A.D. 1000 by the Vikings, who may also have brought with them long-haired cats, like those ancestral to the modern Siberian and Turkish Angora. During World War II, the Norwegian Forest cat was nearly extinct; then the Norwegian Forest Cat Club's breeding program increased the cat's number. It was registered as a breed with the European Fédération Internationale Féline in the 1970s, when a cat fancier, Carl-Fredrik Nordane, took notice of the breed and made efforts to register it. The breed is very popular in Norway, Denmark, Sweden, Iceland, and France. It is a large breed with a strong body, similar to the Siberian and Maine Coon cat breeds, with long legs, a bushy tail, and a sturdy body. It is very good at climbing, partly because of strong claws. The lifespan is usually 14 to 16 years. Kidney and heart diseases have been reported in the breed. Specifically in this breed, complex rearrangements of glycogen branching enzyme (GBE1) can cause a perinatal hypoglycaemic collapse and a late-juvenile-onset neuromuscular degeneration in glycogen storage disease type IV. The Norwegian Forest cat is adapted to survive Norway's cold weather. Its ancestors may include cold-adapted black and white British Shorthair cats brought to Norway from Great Britain some time after 1000 AD by the Vikings, and longhaired cats brought to Norway by Crusaders around the 14th century. These cats could have reproduced with farm and feral stock and may have eventually evolved into the modern-day Norwegian Forest breed. The Siberian and the Turkish Angora, longhaired cats from Russia and Turkey, respectively, are also possible ancestors of the breed.