Autism, attention deficit-hyperactivity disorder, bipolar disorder, major depressive disorder and schizophrenia all share several genetic risk factors, according to a major study.

BBC: Five psychiatric disorders 'linked'

Doctors later diagnosed her with major depressive disorder due to the incident and prescribed her medication for several years, which she took until she got married.

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In Liberia, studies showed that 90% of child soldiers showed evidence of post-traumatic stress disorder (PTSD) and 65% displayed symptoms of a major depressive disorder.

FORBES: For Child Soldiers, Every Day Is A Living Nightmare

Study leader Dr Jeffrey Johnson said more research was needed to see if depression problems in teenagers were an early phase of major depressive disorder or if minor depression earlier in life contributed to the development of more serious problems later on.

BBC: Depressed teens 'face adult risk'