Biomaterial Database

[The diagnosis of mental retardation in fragile X syndrome is revolutionized by molecular genetics]. 1993

M Lemire, and F Rousseau

Unité de recherche en génétique humaine et moléculaire, hôpital Saint-François d'Assise, Québec.

The fragile X syndrome is the most common cause of inherited mental retardation. Clinical signs, which are neither specific to the syndrome nor constant, become apparent late in childhood or after puberty, making early diagnosis difficult on a clinical basis alone. The inheritance of the syndrome is peculiar for an X linked disease, since a high proportion of female carriers show a certain degree of mental retardation and "normal transmitting males" do exist. Affected males can be diagnosed by cytogenetic demonstration of the typical fragile X site but only a minority of female carriers can be identified. This makes genetic counseling difficult. In 1991, the cloning and sequencing of the target site of the mutation marked an important step towards full understanding of the peculiarities of inheritance of the fragile X syndrome. A new type of mutation has been revealed: a multistep "expansion" of a small part of a gene that takes place over several generations. A new diagnostic technique by direct genotypic analysis has been developed. With a very high sensitivity and specificity, this analysis detects affected individuals with a "full mutation" (a large "expansion" associated with abnormal methylation of the surrounding region) and individuals with a "premutation" (smaller "expansion") who do not show mental retardation but are at risk of having affected children or grand children. With the direct DNA analysis at the fragile X locus, it is now possible to diagnose easily those children affected with the syndrome and to offer adequate genetic counseling and prenatal diagnosis to female carriers in affected families.(ABSTRACT TRUNCATED AT 250 WORDS)

UI	MeSH Term	Description	Entries
D008297	Male		Males
D008607	Intellectual Disability	Subnormal intellectual functioning which originates during the developmental period. This has multiple potential etiologies, including genetic defects and perinatal insults. Intelligence quotient (IQ) scores are commonly used to determine whether an individual has an intellectual disability. IQ scores between 70 and 79 are in the borderline range. Scores below 67 are in the disabled range. (from Joynt, Clinical Neurology, 1992, Ch55, p28)	Disability, Intellectual,Idiocy,Mental Retardation,Retardation, Mental,Deficiency, Mental,Intellectual Development Disorder,Mental Deficiency,Mental Retardation, Psychosocial,Deficiencies, Mental,Development Disorder, Intellectual,Development Disorders, Intellectual,Disabilities, Intellectual,Disorder, Intellectual Development,Disorders, Intellectual Development,Intellectual Development Disorders,Intellectual Disabilities,Mental Deficiencies,Mental Retardations, Psychosocial,Psychosocial Mental Retardation,Psychosocial Mental Retardations,Retardation, Psychosocial Mental,Retardations, Psychosocial Mental
D008967	Molecular Biology	A discipline concerned with studying biological phenomena in terms of the chemical and physical interactions of molecules.	Biochemical Genetics,Biology, Molecular,Genetics, Biochemical,Genetics, Molecular,Molecular Genetics,Biochemical Genetic,Genetic, Biochemical,Genetic, Molecular,Molecular Genetic
D002874	Chromosome Mapping	Any method used for determining the location of and relative distances between genes on a chromosome.	Gene Mapping,Linkage Mapping,Genome Mapping,Chromosome Mappings,Gene Mappings,Genome Mappings,Linkage Mappings,Mapping, Chromosome,Mapping, Gene,Mapping, Genome,Mapping, Linkage,Mappings, Chromosome,Mappings, Gene,Mappings, Genome,Mappings, Linkage
D004247	DNA	A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine).	DNA, Double-Stranded,Deoxyribonucleic Acid,ds-DNA,DNA, Double Stranded,Double-Stranded DNA,ds DNA
D005260	Female		Females
D005600	Fragile X Syndrome	A condition characterized genotypically by mutation of the distal end of the long arm of the X chromosome (at gene loci FRAXA or FRAXE) and phenotypically by cognitive impairment, hyperactivity, SEIZURES, language delay, and enlargement of the ears, head, and testes. INTELLECTUAL DISABILITY occurs in nearly all males and roughly 50% of females with the full mutation of FRAXA. (From Menkes, Textbook of Child Neurology, 5th ed, p226)	FRAXA Syndrome,FRAXE Syndrome,Martin-Bell Syndrome,Fra(X) Syndrome,Fragile X Mental Retardation Syndrome,Fragile X-F Mental Retardation Syndrome,Mar (X) Syndrome,Marker X Syndrome,Mental Retardation, X-Linked, Associated With Fragile Site Fraxe,Mental Retardation, X-Linked, Associated With Marxq28,X-Linked Mental Retardation and Macroorchidism,FRAXA Syndromes,FRAXE Syndromes,Fragile X Syndromes,Marker X Syndromes,Martin Bell Syndrome,Syndrome, FRAXA,Syndrome, FRAXE,Syndrome, Fragile X,Syndrome, Marker X,Syndrome, Martin-Bell,Syndromes, FRAXA,Syndromes, FRAXE,Syndromes, Fragile X,Syndromes, Marker X,X Linked Mental Retardation and Macroorchidism
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D014960	X Chromosome	The female sex chromosome, being the differential sex chromosome carried by half the male gametes and all female gametes in human and other male-heterogametic species.	Chromosome, X,Chromosomes, X,X Chromosomes