It is not uncommon for Adenium's to loose their leaves during the fall and winter months especially if they are kept outside in cooler temps. Mine are kept in my greenhouse and are protected from freezing temps but they do get cooler temps so mine usually always loose their leaves.
****So in fall and winter months please be aware that most likely the plant you receive will either have lost its leaves already or will loose them during shipment or soon after shipment. Even during the warmer months it is not uncommon for them to lose their leaves during shipment or soon after from shipping stress.*****
This is no cause for alarm. When temps warm up in the spring they will spout leaves very quickly.
When fed regularly Adenium's actually grow pretty quick
Adenium's have to be protected from freezing temps!!! I recommend protecting them from temps below 40
Don't over water Adenium's. And feed them regularly during the growing months.