|Images are from Wikimedia Commons under Creative Commons licenses: one, two.|
The above dog is a fawn Doberman, and this dog has color dilution alopecia. It is caused by malformation of the folicles, thus leading to hair loss, or alopecia. It is termed "color dilution alopecia" due to the link to the dilution gene, which turn black to blue and liver to fawn. Since it is linked to this dilution, the hair on the body that is red is completely unaffected. The inheritance of the condition is not clear. It can be diagnosed by examining the melanin distribution of the diluted hairs.
Some of the earliest signs of the disease include infection of the affected hair follicles. The hair breaks due to the condition, and may or not grow back after it is initially lost. Some of the ways to prevent breaking of the coat is to not groom the dog very vigorously and to use mild shampoos. The bare skin is sensitive to cold and sun, so car needs to be taken when the dog is exposed to these conditions. Other than the loss of hair, the dog's health will be normal.
It is especially common in Doberman pischers, but is also known to occur in numerous other breeds, such as whippets, dachshunds, great Danes, and Chihuahuas. Interestingly enough, however, not every breed that has the blue dilution gene has color dilution alopecia.
One of my former neighbors has a blue Doberman with color dilution alopecia.
Source is University of Prince Edward Island's Canine Inherited Disorders Database.