Mental retardation function

VLDL receptor Loss-of-function (familial, autosomal recessive) Autosomal recessive cerebellar hypoplasia (ataxia, mental retardation)... 

Zalfa, F. and Bagni, C. Molecular insights into mental retardation multiple functions for the Fragile X mental retardation protein Curr. Issues Mol. Biol. 6 73-88, 2004. 

Clinical findings include mental retardation, severe metabolic acidosis, and evidence of a spastic quadripare-sis and cerebellar disease. Some patients develop normally until late childhood, when a progressive loss of intellectual function became appreciated. Patients also may manifest a mild hemolysis. Pathological changes have included atrophy of the cerebellum and lesions in the cortex and thalamus. There is no specific therapy. 

Definitions of mental illness tend to contain two aspects a normative element and a functional element. Normative definitions delimit abnormal behavior in light of what is typical, usual, or the norm. Some degree of deviance from the norm is necessary for a behavior to be considered abnormal. Deviance alone, however, is never sufficient for a label of abnormality. High IQ is just as deviant as low IQ, but only mental retardation is labeled abnormal. This leads us to the functional element of the definition. Typically, the label of abnormality requires deviance plus maladaptation. Maladaptation suggests some diminished capacity to function relative to an average. For example, the DSM defines mental disorder as a syndrome that is associated with distress or impairment in functioning (American Psychiatric Association, 1994, pp- xxi-xxii). 

In many cases, UPD likely has no effect on health or development. Because most genes are not imprinted, it doesn t matter if a person inherits both copies from one parent instead of one copy from each parent. In some cases, however, it does make a difference whether a gene is inherited from a person s mother or father. A person with UPD may lack any active copies of essential genes that undergo genomic imprinting. This loss of gene function can lead to delayed development, mental retardation, or other medical problems. 

Mental Retardation Refers to sub-average general intellectual functioning which originated during the developmental period and is associated with impairment in adaptive behavior. 

This diversity of mental retardation, in both cause and phenotype, carries important implications for consideration of the biochemistry of consciousness. On the one hand, because this is an investigation of multiple causalities—including, for example, inborn errors of metabolism, each of which has its own unique biochemical profile (Cook Leventhal, 1996), it may not prove possible to identify specific neurotransmitter abnormalities which are common to mental retardation as such. On the other hand common themes concerning key neurotransmitters may be identified from studies of mental retardation. Altered neurotransmitter functioning associated with the severity of mental retardation is open to different interpretations, either reflecting fundamentally impaired development of cerebral structure or a more general impairment of central transmitter activity and functioning. 

Two transmitters have been the subject of most studies in mental retardation serotonin and dopamine and this section focuses on abnormalities in the function of these transmitters, and effects of serotonin- and dopamine-altering drugs. 

If there is an association between the extent or severity of abnormal neurotransmitter functioning and the global measure of severity of autism, the direction and mechanism of causality may still be unclear (as has been discussed in mental retardation). However, neurotransmitter correlates of specific aspects of autism, such as social isolation or obsessional behaviour, are likely to be more revealing and of greater relevance to the study of consciousness. 

Prenatal exposure to ethanol results in a spectrum of abnormalities including, at one extreme, fetal alcohol syndrome, which includes growth retardation, facial anomalies, mental retardation, and microencephaly. Children with less severe prenatal exposures often lack the characteristic facial features of fetal alcohol syndrome, but suffer from a similar pattern of cognitive deficits (Berman and Hannigan, 2000). Mild exposures are associated with variable deficits in motor development and functional delays (Levitt, 1998). 

Sajatovic, M., Ramirez, L.F., Kenny, J.T., and Meltzer, H.Y. (1994) The use of clozapine in borderline-intellectual-functioning and mentally retarded schizophrenic patients. Compr Psychiatry 35 29-33. 

These hormones induce amphibian metamorphosis, the change of a tadpole into a frog—an obviously very complex series of biochemical and developmental reactions. Human fetuses will show skeletal abnormalities as well as neuromuscular and mental retardation if born with an inadequately functioning thyroid gland. 

Thyroid hormone is critical for the development and functioning of nervous, skeletal, and reproductive tissues. Its effects depend on protein synthesis as well as potentiation of the secretion and action of growth hormone. Thyroid deprivation in early life results in irreversible mental retardation and dwarfism—typical of congenital cretinism. 

Hypothyroidism is a syndrome resulting from deficiency of thyroid hormones and is manifested largely by a reversible slowing down of all body functions (Table 38-4). In infants and children, there is striking retardation of growth and development that results in dwarfism and irreversible mental retardation. 

Maple syrup urine disease (MSUD) is a recessive disorder in which there is a partial or complete deficiency in branched-chain o-ketoacid dehydrogenase, an enzyme that decarboxylates leucine, isoleucine, and valine (see Figure 20.10). These amino acids and their corre sponding a-keto acids accumulate in the blood, causing a toxic effect that interferes with brain functions. The disease is characterized by feeding problems, vomiting, dehydration, severe metabolic acidosis, and a characteristic maple syrup odor to the urine. If untreated, the disease leads to mental retardation, physical disabilities, and death. 

Correct answer = B. Phenyllactate, phenyl-acetate, and phenylpyruvate, which are not normally produced in significant amounts in the presence of functional phenylalanine hydroxylase, are elevated in PKU, and appear in the urine. In patients with PKU, tyrosine cannot be synthesized from phenylalanine and, hence, becomes essential and must be supplied in the diet Treatment must begin during the first seven to ten days of life to prevent mental retardation. Discontinuance of the phenylalanine-restricted diet before eight years of age is associated with poor performance on IQ tests. Adult PKU patients show deterioration of attention and speed of mental processing after discontinuation of the diet. Life-long restriction of dietary phenylalanine is, therefore, recommended. 

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