PWDs have a single-layered coat that does not shed (see Moult), and therefore their presence is tolerated well among many people who suffer from dog allergies. Persons with dog allergies, however, should consult their medical advisor before considering the purchase of any dog.Most PWDs, especially those shown in conformation shows, are entirely black, black and white, brown, or silver-tipped; it is common to see white chest spots and white paws or legs on black or brown coated dogs. Overall, white is the least common Portuguese Water Dog color, while black with white markings on the chin ('milk chin') and chest is the most common color. GM1 storage disease, one of a family of conditions called GM1 gangliosidoses, is a recessive, genetic disorder that is inevitably fatal. All breeding stock should be tested for GM-1 storage disease or GM1 gangliosidoses, which is a fatal nerve disease that typically appears when a puppy is approximately six months of age.