biostudies-literatureJayaweera KMedical Research CouncilNational Institute for Health Research (NIHR)e029332https://www.ebi.ac.uk/biostudies/studies/S-EPMC6797400biostudies-literatureUnknown9(10)<h4>Introduction</h4>Worldwide, 10%-20% of children and adolescents experience mental health conditions. However, most such disorders remain undiagnosed until adolescence or adulthood. Little is known about the factors that influence mental health in children and adolescents, especially in low and middle-income countries (LMIC), where environmental threats, such as poverty and war, may affect optimal neurodevelopment. Cohort studies provide important information on risks and resilience across the life course by enabling tracking of the effects of early life environment on health during childhood and beyond. Large birth cohort studies, including twin cohorts that can be aetiologically informative, have been conducted within high-income countries but are not generalisable to LMIC. There are BMJ openProtocol for establishing a child and adolescent twin register for mental health research and capacity building in Sri Lanka and other low and middle-income countries in South Asia.PMC6797400KMRF-2014-03-002NIHR200242MC_PC_MR/R018448/1NIHR200259Nagahawatte AKodituwakku GHelliwell TSamaraweera SYusuf RUdagama PPonnamperuma GDe Alwis SJayaweera KZavos HMSAbeysinghe NAhmad ARijsdijk FSumathipala ABalhara YAndras AHewamalage AJordan KPWickramatilake CSaffery RCraig JMZafar SSelvarathnam LMallen CIves JChonnachtaigh SUGlozier NSimonoff ESaxena AShepherd TDissanayake LDziedzic KBlackburn SRahman OBhan AWe would like to acknowledge the other members of the SEARCH GroupCooray RJayathilake AMakuloluwa TFernando BfalseProtocol for establishing a child and adolescent twin register for mental health research and capacity building in Sri Lanka and other low and middle-income countries in South Asia.<h4>Introduction</h4>Worldwide, 10%-20% of children and adolescents experience mental health conditions. However, most such disorders remain undiagnosed until adolescence or adulthood. Little is known about the factors that influence mental health in children and adolescents, especially in low and middle-income countries (LMIC), where environmental threats, such as poverty and war, may affect optimal neurodevelopment. Cohort studies provide important information on risks and resilience across the life course by enabling tracking of the effects of early life environment on health during childhood and beyond. Large birth cohort studies, including twin cohorts that can be aetiologically informative, have been conducted within high-income countries but are not generalisable to LMIC. There are 2019-01-01T00:00:00Z2019 Oct2025-04-04T07:52:28.314Z2019-11-07T08:06:51ZS-EPMC67974003161942010.1136/bmjopen-2019-029332