Seasonal affective disorder, also known as seasonal depression, causes depressive symptoms during only certain times of the year... and there's a pattern to it?!
The definitive cause is unclear,
Die Ursache ist unklar.
La causa no se conoce,
La causa no se conoce,
On ne connaît pas
les causes exactes.
La causa certa non è ancora chiara,
A causa não é muito clara,