Final Activity Report Summary - CEDY (Frequency of Occurrence of Brain Malformations in a Region (Del-Alfold) in Hungary) Malformations of the central nervous system (CNS) are rather common causes of infant death. Progress in brain imaging and epilepsy surgery revealed that CNS dysgenesis is also a frequently identified cause of developmental delay, intellectual disability, neurological deficit, and intractable epilepsy. The main objective of this project was to perform a population based epidemiological study to reveal the prevalence of CNS malformations in a region (South Great Plain - Dél Alföld) in Hungary. CNS malformation register has been established at the Department of Paediatrics, University of Szeged, Hungary. In addition to the prevalence figures of the major forms of CNS dysgenesis the prevalence of the accompanying congenital anomalies inside and outside the CNS were also studied. The outcome measures of CNS malformations were assessed in terms of developmental delay, intellectual disability, and neurological deficit. The features of epilepsies associated with CNS malformations were recorded as well. Data were collected from paediatric and paediatric neurology clinics in the South Great Plain (Dél-Alföld) region in Hungary and from the Hungarian Birth Defects Register. Detailed history was taken from the parents and clinical assessment, including developmental milestones, mental capabilities, and neurological status was carried out. Cranial CT and MR scans were reviewed for dysgenesis. Electroencephalography was also performed. The prevalence of CNS malformations per 10 000 live births was calculated. The total number of CNS malformations was 217 in a population of 185.486 live births from 1 July 1992 to 30 June 2006 (14 years). The prevalence of CNS dysgenesis was 11.69 per 10 000 live births. The prevalence for males was 12.60 while it was 10.75 for females. The major CNS malformation was accompanied by another malformation in the CNS in 29.4 % of the cases, while CNS dysgenesis was associated with congenital anomalies outside the CNS in 33.6 % of the cases. The localisation-specific prevalence was the highest for myelomeningocele (2.05) followed by microcephaly (1.94) corpus callosum malformations (1.73) and hindbrain (cerebellum, pons, and medulla) malformations (1.56). The prevalence of migration defects, polymicrogyria, schizencephaly, malformations of the corpus callosum, and arachnoid cysts was higher in boys than in girls, while the prevalence of encephalocele, microcephaly, and hindbrain malformations was higher in girls. Sixteen patients (7.4 %) out of 217 live births with CNS malformations died in the neonatal period. Developmental delay was observed in 64.2 %, intellectual disability in 47.3 %, while neurological deficit in 56.2 % of the patients surviving the neonatal period. Epilepsy was diagnosed in 35.3 % of patients beyond the neonatal period. Including induced terminations and stillbirths the prevalence of myelomeningocele, anencephaly, and encephalocele was 3.99 2.16 and 0.75 respectively. The prevalence data in this study are in good agreement with figures published from various parts of the world in the last few years. These data reflect the real impact of CNS dysgenesis on child development. The CNS malformation register will be the basis of further investigations to identify environmental, epigenetic and genetic causes of CNS dysgenesis and characterise epilepsies associated with brain malformations.