Kallmann syndrome can cause depression in a number of ways.
There is the social isolation before diagnosis, the feeling of being the only person in the world not going through puberty and feeling alone with condition when everybody else is growing up.
Having Kallmann syndrome when other brothers and sisters are developing normally can cause depression.
The variation in hormone levels in between injections can be difficult to cope with, especially if the levels fall too low.
Feeling "different" from everybody else and not feeling "normal", even when on treatment can cause depression in some patients. Being under developed physically can lead to low self worth and self esteem.
Infertility, for both the males and females can be difficult especially later in life when it feels like everybody else around you is having children.
Kallmann syndrome is a difficult condition to describe to other people and not having people to open up to or talk freely too can lead to depression.