Alopecia, or hair loss, can be due to a number of different causes. Endocrine (hormonal) imbalances are one cause. Alopecia due to endocrine imbalance is often accompanied by hyperpigmentation (dark or black skin where the hair is missing). Possibilities for this imbalance include hypothyroidism, hyperadrenocorticoidism (Cushing's syndrome), and hyper or hypoestrogenism. Hair loss (or lack of development) can also be caused by a vitamin A deficiency. It is also possible that this is an inherited trait somewhere in one of the parents lines. It could also be something as simple as he was not quite finished developing at the time of his birth. If I am not mistaken (and I might well be) hair is one of the final stages of development in most species. I think your best option at this point is to discuss this with your vet and get his opinion as to what course of testing and / or treatment should follow. At this point he is a little young to be put through a great deal of testing but it would be a good idea to have your vet take a look at him to rule out the possibility of this being a serious problem.

I hope this helps. please let me know if you need further information.