A hereditary mental disorder, partially explained by genomic imprinting and the addition of nucleotides to a triplet repeat near the end of an X chromosome. frameshift mutation A mutation occurring when the number of nucleotides inserted or deleted is not a multiple of 3, thus resulting in improper grouping into codons. free energy A quantity of energy that interrelates entropy (S) and the system's total energy (H); symbolized by G. The change in free energy of a system is calculated by the equation G = ΔH – T ΔS, where T is absolute temperature. free energy of activation The initial investment of energy necessary to start a chemical reaction; also called activation energy. frequency-dependent selection A decline in the reproductive success of a morph resulting from the morph's phenotype becoming too common in a population; a cause of balanced polymorphism in populations. fruit fructus, fruit] A mature ovary of a flower that protects dormant seeds and aids in their dispersal.
an inherited condition in which the X chromosome - is slightly abnormal. Further info.
An X-linked disorder which presents as dysmorphic features (an elongated face, large ears, prominent jaw, and macroorchidism, or enlarged testes, and mental retardation.
a common type of inherited mental disability, caused by a defective gene on the X chromosome.
An X-linked disorder that is the most common genetically inherited form of mental retardation currently known. Boys who inherit a Fragile X gene mutation usually develop the disorder, while girls who inherit the mutation are more likely to be carriers. (The mutation is unstable and tends to increase in size over succeeding generations, so that girls may eventually be affected as well, though the mental retardation is not as severe as in boys.) If you have a family history of mental retardation, testing can determine whether Fragile X is responsible and whether you are a carrier.
A frequent genetic cause of mental retardation. A mutation causes a repetition of the letters CGG in a gene on the X chromosome. The more repeats of this code on a person's X chromosome, the more impaired he or she is likely to be.
is a spectrum of symptoms that correlate with autistic disorder, in this case resulting from a defect on the X chromosome. It affects males more severely with mental retardations, severe communicative problems and repetitive behaviors. Females are generally socially withdrawn and have borderline intelligence; they are also subject to mood disorders.
An inherited chromosomal abnormality that leads to learning difficulties and mental handicap. So called because the X chromosome possesses a site of fragility.
a syndrome resulting from a fragile or broken site on the X chromosome, often characterized by mental retardation, hypotonia and hyperactivity
Malformation (or even breakage) of the X chromosome associated with moderate mental retardation. Symptoms include large, underdeveloped ears, a long, thin face, a broad nasal root, and enlarged testicles in males; many individuals show attention deficits and hyperactivity.
One of the most common causes of inherited mental retardation and neuropsychiatric disease in human beings, affects as many as one in 2000 males and one in 4000 females. The syndrome is also known as FRAXA (the fragile X chromosome itself) and as the Martin-Bell syndrome. However, the preferred name is fragile X syndrome. See the entire definition of Fragile X syndrome
After Down syndrome, the second most frequent genetic cause of mental retardation. The disorder is one of a group of diseases that results from an unusual kind of mutation: a repeating sequence of three letters of the DNA code, called a triplet repeat or trinucleotide repeat. In Fragile X, the repeating triplet is CGG, cytosine-guanine-guanine, in a gene on the X chromosome. The larger the number of repeats they possess, the more likely patients are to be seriously impaired. People who possess just a few repeats are carriers but often not affected.
a common hereditary cause of mental impairment that affects males about twice as often as females, and can result in learning disabilities; attention, hyperactivity, and behavioral challenges; speech and language delays; and autistic-like behaviors. Physical characteristics—which may not appear until after puberty—include loose joints, especially the fingers; long, narrow face; prominent ears, jaw, and forehead; flat feet; and enlarged testicles. IQs of males with fragile X appear to decline throughout childhood, resulting in mildly impaired adults. While some females with fragile X have significant intellectual impairment, the majority has either normal IQ or learning disabilities.
A genetic condition caused by an unusualfragile site on one of the gender determining chromosomes (i.e., the X chromosome); the most common inherited cause of mental retardation.
A genetic condition in which one part of the X chromosome has a defect. The condition causes mental retardation. It has also been reported with learning disabilities, autism, speech and language disorders, and mathematics and motor disabilities.
this the #1 inherited cause of mental retardation, affecting an estimated 1 in 2000 males and 1 in 4000 females of all races. it is relatively unknown and often misdiagnosed.
A-Z reference book of syndromes Learning disability due to a defect in a particular part of the X chromosome.
Fragile X syndrome, also known as Martin-Bell syndrome, is a genetic disorder that is the most common form of inherited mental retardation. Individuals with this disorder often have distinctive physical features, such as a long face and large prominent ears. People with Fragile X syndrome experience some degree of mental retardation along with speech and language delays. In addition, 15-20% may also exhibit behaviors associated with autism.
A genetic condition related to the X chromosome that affects mental, physical and sensory development.
Disorder associated with a pinched region of the X chromosome; a leading genetic cause of mental retardation in males.
The commonest cause of severe mental retardation in males, caused by a long "triple repeat sequence" in a part of a gene for intelligence located on an X-chromosome, rendering this sex chromosome susceptible to breakage, which can be revealed either in a karyotype performed under special laboratory conditions or using a special PCR DNA test; females have two X-chromosomes and so may be carriers for this devastating condition, which will affect one-in-two of their male children; the carrier state in females can have clinical effects, namely a susceptibility to reduced numbers of ovarian follicles and hence primary ovarian failure and premature menopause, so should be looked for before assisted conception attempts are made in these clinical circumstances.
Fragile X syndrome, also known as the Martin-Bell syndrome, is a syndrome of X-linked mental retardation. Boys with the syndrome may have large testes (macroorchidism), prognathism, hypotonia and autism, and a characteristic but variable face with large ears, long face, high-arched palate, and malocclusion. Additional abnormalities may include lordosis, heart defect, pectus excavatum, flat feet, shortening of the tubular bones of the hands, and joint laxity.