title: Aetiology of severe mental retardation and further genetic analysis by high-resolution microarray in a population-based series of 6- to 17-year-old children.
abstract: OBJECTIVE
  To investigate the prevalence, co-morbidities and aetiologies of severe mental retardation (SMR) in a cohort of Swedish children and to further penetrate aetiologies in the group with undetermined causes by application of updated clinical-genetic methods.
  
  
  METHODS
  The study was population-based and included children living in the County of Halland in western Sweden in 2004 (born 1987-1998; 46,000 children). Patients were identified through habilitation centres, paediatric clinics and school health services. Patients with unclear prenatal aetiology were investigated with single nucleotide polymorphism (SNP)-array.
  
  
  RESULTS
  Severe mental retardation was identified in 133 children from 132 families, corresponding to a prevalence of 2.9 per 1000 children. There were more males than females (90:43).The aetiology was prenatal in 82 (62%), perinatal in 14 (10%) and postnatal in 8 (6%). In 29 (22 %) children, mainly males with autism, the cause could not be related to the time of birth. In the prenatal group, genetic causes dominated, but still 23 children remained undiagnosed; in 5/19 of these patients, a diagnosis could be made after SNP-array analysis. One or more associated neurological handicaps were found in more than half of the children.
  
  
  CONCLUSIONS
  Prevalence and co-morbidity were similar to previous Scandinavian studies. High-resolution chromosomal micro-array techniques are valuable diagnostic tools, reducing the number of patients with unexplained SMR.
authors.affiliation: Department of Paediatrics, Halland County Hospital, Halmstad, Sweden. mikael.lundvall@karolinska.se
authors.forename: Mikael
authors.initials: M
authors.lastname: Lundvall
authors.forename: Saideh
authors.initials: S
authors.lastname: Rajaei
authors.forename: Anna
authors.initials: A
authors.lastname: Erlandson
authors.forename: Mårten
authors.initials: M
authors.lastname: Kyllerman
mesh_terms: D000293:Adolescent; D002648:Child; D015331:Cohort Studies; D015897:Comorbidity; D005260:Female; D006801:Humans; D008607:Intellectual Disability / Q000453:epidemiology* / Q000209:etiology* / Q000235:genetics; D008297:Male; D046228:Microarray Analysis / Q000379:methods; D020641:Polymorphism, Single Nucleotide; D015995:Prevalence; D012720:Severity of Illness Index; D017678:Sex Distribution; D013548:Sweden / Q000453:epidemiology