Mental retardation in Finland

Mental retardation affects about 0.6 % of the finnish population (IQ less than 70). There are some rare disorders, like AGU, INCL, Salla disease and Cohen syndrome, which are a part of Finnish disease heritage, but most common syndromes are Down (trisomy 21) and Fragile X.

Von Wendt and Rantakallio (Upsala journal of medical sciences Supplement 1987) studied the occurrence and aetiology of mild mental retardation (IQ 50-70) and borderline retardation (IQ 71-85) on the basis of a one-year (1966) birth cohort of 12,058 live-born infants, which were followed prospectively up to the age of 14 years. The cumulative incidences for mild mental retardation were 5.5/1,000 and borderline retardation 13.4 per 1,000. In the borderline group there was a male preponderance of 2.3/1 as compared to 1.2/1 in mild mental retardation group.

Matilainen et al. (Acta paediatrica 1995) studied causes of mental retardation as part of a multidisciplinary epidemiological case-control study in 151 mentally retarded patients identified by screening four age cohorts (12,882 children) at 8-9 years of age in the province of Kuopio. Genetic causes were found in 28% of all 151 cases; the three most common subgroups were trisomy 21 (13%), fragile X syndrome (4%) and aspartylglycosaminuria (2% ).

Haataja et al. (Human genetics 1994) wrote that the majority of present-day fragile X mutations in Finland may have a common initial ancestor, probably from the 16th century.

Heikura, Taanila, Olsen et al. (American Journal on Mental Retardation 2003) followed two separate, genetically homogeneous cohorts of children born in 1966 (n = 11,965) and 1985–1986 (n = 9,432) in Northern Finland to determine temporal changes in the incidence and prevalence of subcategories of intellectual disability within the same geographic area. The children were followed up to the age of 11.5 years. There was no change in the total incidence (12.62/1,000 in each) or in total prevalence (11.03/1,000 vs. 11.23/1,000) of intellectual disability. However, in the subcategories of intellectual disability, there was a shift from severe and moderate towards mild; whereas profound intellectual disability remained at the same level. The temporal changes followed generally similar patterns by gender.

Phenylketonuria

According to CHC Wausau Hospital Medical Library page (2001) phenylketonuria (PKU) is an inherited metabolic disorder that can result in mental retardation and other neurological problems. People with this disease have difficulty breaking down and metabolizing the amino acid phenylalanine. The incidence of PKU is approximately 1/15,000. In Finland, the incidence is less than 1/100,000 births.

Aspartylglycosaminuria (AGU)

According to GAPS-page (2005) aspartylglycosaminuria is a genetic disorder that is found most commonly in persons of Finnish decent. It is a lysosomal storage disease that becomes apparent after the infant is a few months old. Major symptoms may include coarse facial features, spine and eye deformities, behavior problems and mental retardation. The disorder is caused by an glycoprotein enzyme deficiency. The recessive gene responsible for the disorder is located on the 4th chromosome at 4q21.

Salla disease

R. Froissart and I. Maire wrote in their Orphanet-article (2003) about Free Sialic Acid Storage Disease (SSD), also known as Salla disease. It is a lysosomal storage disease, due to a defective sialic acid transporter in the lysosome membrane normally ensuring the efflux of free sialic acid outside the lysosome. The condition is autosomal recessive and very rare - except in Northern Finland where an estimated 1/40 people are carriers.

Salla disease presents in utero with fetal hydrops and ascites or at birth with hypotonia, hepatosplenomegaly often associated with ascites, coarse facies, bone malformations, severe motor disorders, mental retardation, and seizures.

Infantile neuronal ceroid lipofuscinosis

The neuronal ceroid lipofuscinoses (NCL or CLN) is a mixed group of genetic progressive storage disorders of the brain and eyes with mostly autosomal recessive inheritance. NCL affects 1 per 20,000 to 100,000 in the general population.

Estimated percentage of Infantile neuronal ceroid lipofuscinosis (INCL) is 11-23% (Celia H Chang, eMedicine 2004). According to Findis.org (2004) incidence in Finland is 1/14,000. Onset in INCL is between ages 6 and 24 months. Symptoms are clumsiness, hypotonia, irritability, seizures and ataxia, microcephaly, retinal changes and severe cerebral atrophy. Life expectancy is between 5 and 10 years.

Finnish variant of late infantile neuronal ceroid lipofuscinosis (LINCL)

According to Findis.org (2004) the variant form of LINCL has clinical resemblance both with the classical late infantile type, LINCL and the juvenile type, JNCL, but it is caused by mutation of distinct gene at chromosome 13q22. Incidence in Finland is 1/59,000.

Northern epilepsy (NCL8)

S. Aymé (Orphanet 2002) wrote about Finnish type epilepsy-mental deterioration. It is a form of childhood epilepsy occurring in northern Finland. The patients are normal at birth and develop normally until school age. Age at onset is 5 to 10 years, the patients presenting with generalized tonic-clonic seizures. Inheritance is recessive.

Syndrome is caused by mutations in the CLN8 gene (gene map locus 8pter-p22). Incidence in Finland is 1/176,000.

Cohen syndrome

Symptoms are obesity and hypotonia in association with delayed mental development, characteristic facies, and slender hands and feet. The syndrome is divided into two forms: one which is manifested by the symptoms as outlined by Cohen and the other characterized by chorioretinal dystrophy, leukopenia, and lack of obesity, known as the Norio syndrome. According to C. García Ballesta (Orphanet 2004), nearly 100 cases had been reported.

This rare disease is overrepresented in Finland. Satu Kivitie-Kallio studied the syndrome in 1999. Nationwide examinations were performed on 29 Cohen patients, who form a highly homogenous group aged from 11 months to 57 years.

Autism

According to NIDCD Glossary (2005) autism is a brain disorder that begins in early childhood and persists throughout adulthood; affects three crucial areas of development: communication, social interaction, and creative or imaginative play.

Kielinen, Rantala et al. (Autism. 2004) conducted a population-based survey among 152,732 children and adolescents aged under 16 years and living in northern Finland. 180 children with autistic disorder were identified. Associated medical disorders or associated disorders of known or suspected genetic origin were found in 12.3%, including tuberous sclerosis, Down syndrome, fragile X syndrome, Klinefelter syndrome, XYY syndrome, chromosome 17 deletion, chromosome 46, XX, dup(8) (p) and mitochondriopathy. Other associated disorders identified were epilepsy, hydrocephalus, foetal alcohol syndrome and cerebral palsy. Hearing impairments were found in 8.6% and severe impairment of vision in 3.7%t of the individuals with autistic disorder.

Marko Kielinen (Oulun yliopisto 2005) studied a prevalence of autism in northern Finland. The data were collected from hospital records and the records of the central institutions for the intellectually disabled in the Provinces of Oulu and Lapland in 1996–1997. The age-specific prevalences obtained in this study showed the prevalence to be lowest, i.e. 6.1 per 10,000, in the oldest age group of 15- to 18-year-old adolescents and highest, i.e. 20.7 per 10,000, in the age group of 5- to 7-year-old children, when the criteria of ICD-10 and DSM-IV were used. In this study, almost 50% of the autistic cases had a tested IQ above 70. Associated medical disorders or associated disorders of known or suspected genetic origin were diagnosed in 12.3%. Other associated medical disorders were epilepsy, hydrocephalus, fetal alcohol syndrome and cerebral palsy. Severe impairment of vision was evident in 3.7%.

About three- to fourfold prevalence of autistic disorders in Northern Finland was found when compared to 16 years ago, Kielinen mentioned.

PEHO syndrome

PEHO syndrome (Progressive encephalopathy with Edema, Hypsarrhythmia, and Optic atrophy) is an autosomal recessive disorder leading to profound psychomotor retardation. Incidence in Finland was 1/78 000 in 2004. Only few patients fulfilling the diagnostic criteria for PEHO syndrome had been reported outside Finland.

More information:

A population-based study on the causes of mild and severe mental retardation, Matilainen R, Airaksinen E, Mononen T, Launiala K, Kaariainen R, Acta Paediatr. 1995 Mar;84(3):261-6 - PubMed
Aspartylglycosaminuria, Genetic Information and Patient Services, Inc. (GAPS 2005)
Associated medical disorders and disabilities in children with autistic disorder: a population-based study, Kielinen M, Rantala H, Timonen E, Linna SL, Moilanen I, Autism. 2004 Mar;8(1):49-60 - PubMed
AUTISM IN NORTHERN FINLAND, A prevalence, follow-up and descriptive study of children and adolescents with autistic disorder, Marko Kielinen, OULUN YLIOPISTO, OULU 2005 (pdf)
Autism, Nemours Foundation
Autism Spectrum Disorders (Pervasive Developmental Disorders), NIMH
Autism - Wikipedia

Ceroid lipofuscinosis, neuronal, A. Kohlshütter, Orphanet
CEROID LIPOFUSCINOSIS, NEURONAL 8; CLN8, OMIM, Victor A. McKusick, George E. Tiller
Cognitive Disability / Mental Retardation - Family Village Library
Cohen syndrome - a clinical study of 29 Finnish patients, Satu Kivitie-Kallio, Helsingin yliopiston verkkojulkaisut Helsinki 1999 (pdf)
Cohen syndrome, C. García Ballesta, Orphanet
Core Health Indicators from the WHR 2006
Craniofacial features in Cohen syndrome: an anthropometric and cephalometric analysis of 14 patients, Hurmerinta K, Pirinen S, Kovero O, Kivitie-Kallio S, Clin Genet. 2002 Aug;62(2):157-64 - PubMed
Diagnostic criteria and genetics of the PEHO syndrome, Somer M, J Med Genet. 1993 Nov;30(11):932-6 - PubMed
Down Syndrome Information Network
Down Syndrome: Health Issues - Medical Essays and Information by Len Leshin
Down Syndrome WWW Page
Epilepsy mental deterioration finnish type, Dr S. Aymé, Orphanet 2002

Finnish Disease Heritage, Findis.org
Finnish Disease Heritage I: characteristics, causes, background, Norio R, Hum Genet. 2003 May;112(5-6):441-56
Finnish Disease Heritage II: population prehistory and genetic roots of Finns, Norio R, Hum Genet. 2003 May;112(5-6):457-69 - PubMed
Finnish variant of late infantile neuronal ceroid lipofuscinosis, Findis.org
Fragile X Syndrome, Robert A Saul, Jack C Tarleton, GeneReviews
FRAGILE X SYNDROME IN NORTHERN FINLAND, Molecular, diagnostic and population genetic aspects, Marja-Leena Väisäne Department of Clinical Genetics, University of Oulu 1999 (pdf)
Free sialic acid storage disease, Orphanet, R. Froissart, I. Maire, 2005

Glossary [NIDCD]
MedlinePlus: Phenylketonuria
MedlinePlus Medical Encyclopedia: Mental retardation
Mental Retardation, Karen H Harum, eMedicine
Mental retardation - Wikipedia, the free encyclopedia
Mild mental retardation in northern Finland, von Wendt L, Rantakallio P, Ups J Med Sci Suppl. 1987;44:47-51 - PubMed
Neuronal Ceroid Lipofuscinoses, Celia H Chang, eMedicine

Phenylketonuria, CHC Wausau Hospital Medical Library 1999-2001, The Thomson Corporation
Prenatal diagnosis of single gene disorders in northern Finland, Leisti J, Jouppila P, Mustonen A, Kahkonen M, Herva R, Ruokonen A, Kirkinen P, Ann Med. 1990 Apr;22(2):123-9 - PubMed
Prevalence of the fragile X syndrome in four birth cohorts of children of school age, Kahkonen M, Alitalo T, Airaksinen E, Matilainen R, Launiala K, Autio S, Leisti J, Hum Genet. 1987 Sep;77(1):85-7 - PubMed

Temporal Changes in Incidence and Prevalence of Intellectual Disability Between Two Birth Cohorts in Northern Finland, Ulla Heikura, Anja Taanila, Päivi Olsen, Anna-Liisa Hartikainen, Lennart von Wendt and Marjo-Riitta Järvelin, American Journal on Mental Retardation 108/1, January 2003
The Arc's Q & A on PKU 2005
The fragile X syndrome in Finland: demonstration of a founder effect by analysis of microsatellite haplotypes, Haataja R, Vaisanen ML, Li M, Ryynanen M, Leisti J, Hum Genet. 1994 Nov;94(5):479-83 - PubMed
The National Fragile X Foundation - Fragile X Syndrome

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Kari Viitapohja 30.1.2005