HOPKINS, MI -- Mike and Heather Ludlam have raised sheep on their farm in Hopkins since 1993, carefully selecting stock to expand their purebred heritage Shetland and Targhee breeds.

They have sold breeding stock, lamb, raw fleeces, and rovings all produced on the farm.

These days, though, the Ludlams are carefully selecting for a different breed of sheep with a different goal in mind -- testing and selecting lambs that bear a recessive gene for a devastating sheep disease.

Although the disease would prevent them from ever reaching adulthood, the lambs are extremely valuable store of a substance researchers need as they formulate new treatments for Huntington's disease and similar neurological disorders in humans.

For the Ludlams, the mission is personal.

Mike's Ludlam's sister Dory died of Huntington's disease in March 2012 at the age of 51 after suffering years of debilitating mental and physical decline that saw her slide from a sharp, outgoing businesswoman to a state of helplessness that left her in a care facility for the final years of her life.

Huntington's is an incurable hereditary illness. Because Mike and Dory were both adopted, and not blood siblings, he is at no greater risk of developing the disease than anyone in the general population. But Dory's children have a 50 percent chance of developing the disease themselves in later adulthood.

At least they are forewarned of the possibility. Dory Ludlam was born in an era when closed adoptions were the norm and she had no records of her birth parents' medical histories. Her mental health began to deteriorate in her 30s, but it wasn't until physical symptoms began that doctors finally pinned down a diagnosis for her disease.

"It came out of nowhere, and was so devastating to our whole family," Heather Ludlam said.

So when Mike saw a little one-paragraph blurb about sheep with a certain genetic trait could be used to study Huntington's, his interest was piqued.

Heather, a veterinarian, began to see similar notices in other trade publications. Last February, the Ludlams visited Dr. Larry Holler, the veterinarian in South Dakota who had researched the sheep disease, GM1 gangliosidosis, for his PhD project.

They learned that while all mammals produce the substance GM1 ganglioside, sheep with this genetic flaw produce levels 40 times higher than healthy cows or sheep. It's that substance, harvested from the brain, spinal column and organs of the lambs, that researchers are using to create a treatment for human illness.

The lambs do not suffer for the cause.

They would not begin to develop symptoms of the disease until they are 5-6 months old, the age at which they would be slaughtered for market anyway.

Their genetic makeup can be determined by a simple blood test when they are a few days old and those that test positive for the disease are separated out and sold for research at weaning.

Those shown to be carriers of the disease can be kept on as breeding animals, sold to other sheep farmers raising flocks for research, or sold as market lambs since the genetic flaw does not affect the meat.

Selective breeding for the genetically damaged lambs isn't difficult, and assures a source of the substance needed for clinical trials in Huntington's disease, Parkinson's disease, spinal cord injury and stroke, Heather Ludlam said.

The Ludlam's bought two carrier rams in February, animals that carry the faulty gene but do not demonstrate symptoms of the disease. They bred all of their ewes to them, and of the 47 live lambs born, 26 are carriers.

They will keep the best of the carriers for breeding stock, Heather Ludlam said, and when a carrier ram is bred with a carrier ewe, about 25 percent of the resulting lambs should test positive for the disease.

Fifty percent will carry the gene, and another 25 percent will not have the faulty gene at all.

"It will take a lot of these sheep to treat the 30,000 people in North America with Huntington's," Heather Ludlam said.

While sheep farmers work to raise enough research animals, researchers are working to develop safe forms of the substance collected from the lambs, that can be injected or inhaled.

Their results testing on mice are very promising, with mice affected by Huntington' s quickly regaining normal motor function after a few injections of the substance collected from the lambs' brains.

In January 2015, the U.S. Food and Drug Administration gave investigative approval to ovine GM1 to go through studies that are the first step toward clinical trials.

"When we heard of the possibility of raising sheep with a genetic trait that might help treat patients with Huntington's disease, we immediately felt called upon to become a part of the project," Heather Ludlam said. "It is amazing to finally be able to do something to fight Huntington's disease after all these years. We are committed to raising these sheep and also committed to helping find the funds to bring GM1 to human clinical trials."

Click here to see The Shepherd's Gift, an online fundraising effort to raise money for that research effort.

Rosemary Parker is a reporter for the Kalamazoo Gazette and MLive.com. Contact her at rparker3@mlive.com.