Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0025362 (mental retardation)
 15,878 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ethanol exposure during development is teratogenic. The central nervous system (CNS) is particularly susceptible to ethanol toxicity. In fact, heavy gestational ethanol consumption is one of the leading known causes of mental retardation in the Western world. Ethanol exposure disrupts the proliferation of glia and neuronal precursors in the developing CNS. Depending upon cell population and blood ethanol concentration, ethanol can either inhibit or stimulate cell proliferation. Two features of cell proliferation that are affected by ethanol exposure are the growth fraction (the proportion of cells that is actively cycling) and the cell cycle kinetics, particularly in the length of the G1 phase of the cell cycle. Cell proliferation in the developing CNS reflects the action of positive (mitogenic growth factors) and negative (anti-proliferative factors) regulators. Increasing evidence shows that ethanol interferes with the action of growth factors. In vitro systems are a good model to investigate ethanol neurotoxicity, since the effects of ethanol on cultured cells parallel the effects of ethanol in the developing CNS. The inhibitory effects of ethanol on cell proliferation may result from interference with mitogenic growth factors (e.g., bFGF, EGF, PDGF, IGF-I). Conversely, the stimulatory effects of ethanol may result from the interference with growth inhibiting factors (e.g., TGFbeta1). Interestingly, both in vivo and in vitro studies show that proliferating neural cells display differential sensitivity to ethanol. This differential sensitivity correlates with their response to mitogenic growth factors; that is, cells that are actively regulated by mitogenic growth factors are much more susceptible to ethanol than cells that are less or unresponsive to such factors. Ethanol interference with growth factor action could occur at three levels: ligand production, receptor expression, and/or signal transduction. Thus, ethanol-induced alterations in the developing CNS that characterize fetal alcohol syndrome apparently result from alterations in the regulatory action of growth factors.
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PMID:Growth factor-mediated neural proliferation: target of ethanol toxicity. 962 17

The insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) are important regulators of growth and metabolism and are the key mediators of the actions of growth hormone (GH). Children born small for gestational age (SGA) have a host of medical problems including an increased risk of poor growth later in life, a tendency to develop metabolic abnormalities and a high incidence of learning disabilities. IGFs and related molecules may be linked to all of these concerns. Mouse models of IGF-I and IGF-II deficiencies have phenotypes reminiscent of human SGA, including slow growth, insulin resistance, and mental dysfunction. Humans with IGF-I mutations are born SGA and exhibit very poor subsequent growth, metabolic syndrome and mental retardation. Current management of children born SGA who present with growth failure during childhood includes treatment with GH. SGA children usually have growth factor levels within the normal range; however, as a group, they display lower IGFBP-3 levels in relation to their IGF-I levels. GH is effective in improving growth in children born SGA, but higher doses of GH are required to achieve optimal outcome, suggesting a component of GH insensitivity in SGA children. As in other indications for GH, a rational monitoring approach (focusing on maintaining IGF levels in the high normal range) is prudent.
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PMID:Insulin-like growth factors and their binding proteins in children born small for gestational age: implication for growth hormone therapy. 1467 8

We have previously described the phenotype resulting from a missense mutation in the IGF-I gene, which leads to expression of IGF-I with a methionine instead of a valine at position 44 (Val44Met IGF-I). This mutation caused severe growth and mental retardation as well as deafness evident at birth and growth retardation in childhood, but is relatively well tolerated in adulthood. We have conducted a biochemical and structural analysis of Val44Met IGF-I to provide a molecular basis for the phenotype observed. Val44Met IGF-I exhibits a 90-fold decrease in type 1 IGF receptor (IGF-1R) binding compared with wild-type human IGF-I and only poorly stimulates autophosphorylation of the IGF-1R. The ability of Val44Met IGF-I to signal via the extracellular signal-regulated kinase 1/2 and Akt/protein kinase B pathways and to stimulate DNA synthesis is correspondingly poorer. Binding or activation of both insulin receptor isoforms is not detectable even at micromolar concentrations. However, Val44Met IGF-I binds IGF-binding protein-2 (IGFBP-2), IGFBP-3, and IGFBP-6 with equal affinity to IGF-I, suggesting the maintenance of overall structure, particularly in the IGFBP binding domain. Structural analysis by nuclear magnetic resonance confirms retention of near-native structure with only local side-chain disruptions despite the significant loss of function. To our knowledge, our results provide the first structural study of a naturally occurring mutant human IGF-I associated with growth and developmental abnormalities and identifies Val44 as an essential residue involved in the IGF-IGF-1R interaction.
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PMID:Structural and functional characteristics of the Val44Met insulin-like growth factor I missense mutation: correlation with effects on growth and development. 1557 56

IGF-I is a key factor in intrauterine development and postnatal growth and metabolism. The secretion of IGF-I in utero is not dependent on GH, whereas in childhood and adult life, IGF-I secretion seems to be mainly controlled by GH, as revealed from studies on patients with GHRH receptor and GH receptor mutations. In a 55-yr-old male, the first child of consanguineous parents, presenting with severe intrauterine and postnatal growth retardation, microcephaly, and sensorineural deafness, we found a homozygous G to A nucleotide substitution in the IGF-I gene changing valine 44 into methione. The inactivating nature of the mutation was proven by functional analysis demonstrating a 90-fold reduced affinity of recombinantly produced for the IGF-I receptor. Additional investigations revealed osteoporosis, a partial gonadal dysfunction, and a relatively well-preserved cardiac function. Nine of the 24 relatives studied carried the mutation. They had a significantly lower birth weight, final height, and head circumference than noncarriers. In conclusion, the phenotype of our patient consists of severe intrauterine growth retardation, deafness, and mental retardation, reflecting the GH-independent secretion of IGF-I in utero. The postnatal growth pattern, similar to growth of untreated GH-deficient or GH-insensitive children, is in agreement with the hypothesis that IGF-I secretion in childhood is mainly GH dependent. Remarkably, IGF-I deficiency is relatively well tolerated during the subsequent four decades of adulthood. IGF-I haploinsufficiency results in subtle inhibition of intrauterine and postnatal growth.
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PMID:Homozygous and heterozygous expression of a novel insulin-like growth factor-I mutation. 1576 76

The Rubinstein-Taybi syndrome (RTS) is a rare but well-defined condition characterized by growth and mental retardation, broad thumb-hallux, and distinctive facial features. Ten unrelated Taiwanese children (6 boys and 4 girls) with clinical features suggestive of RTS were evaluated. The associated anomalies included cryptochidism (6/6 males), microcephaly (9/10), congenital heart diseases (8/10), pectus excavatum (5/10), low IGF-I level (4/10), strabismus/nystagmus (4/10), epilepsy (3/10), glaucoma (2/10), cleft palate (2/10), web neck (2/10), limb hypoplasia (2/10), sleep apnea (1/10), and vesico-ureteral reflux (1/10). All of them had normal thyroid function. High-resolution chromosome studies by both G- and R-banding were applied to detect any microscopic chromosomal deletion, particularly over the 16p13 region (responsible for RTS locus). A panel of five cosmids spanning the human cyclic AMP-responsive element binding (CREB) binding protein (CREBBP or CBP) gene in terms of RT100, RT102, RT191, RT203 and RT166 (Leiden, the Netherlands) were used for fluorescence in situ hybridization on the metaphases of those patients. Three cases showed whole or partial deletion of one copy of the CBP gene. Thus, the rate for detecting interstitial submicroscopic deletion of this region by FISH was about 30% in these RTS patients. The disease severity seemed to be correlated with size of the deletion.
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PMID:Rubinstein-Taybi syndrome: clinical and molecular cytogenetic studies. 1623 61

Costello syndrome is characterized by facial dysmorphia, hyperpigmented skin, palmar and plantar hyperkeratosis, curly hair, perioral and nasal papillomata (more rarely localized anally and on vocal cords), short stature, mental retardation and sociable personality. Although growth retardation is typical of Costello syndrome, its cause is not defined. We report on a 10-yr-old Caucasian girl affected by Costello syndrome with fasting hypoglycemia and short stature, associated low circulating levels of acid-labile subunit (ALS), relatively low levels of IGF-I and IGFBP-3, and normal IGF-II, mostly circulating in a binary complex with IGFBP-2 and -6 instead of in a 150 kDa ternary complex. The reduced ALS concentration and the consequent impaired formation of the circulating 150 kDa ternary complex can induce an accelerated clearance rate of IGF peptides and of IGFBP-3, contributing to the decreased IGF-I growth promoting activity in our patient. Moreover, the presence of IGF-II in the binary complex, which has been postulated to increase the insulin-like effects of these peptides, can explain, at least in part, the patient's asymptomatic fasting hypoglycemia.
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PMID:The IGF system in a case of Costello syndrome. 1668 42

We report on a 13-year-old girl who was the first child of nonconsanguineous parents, and who suffered from short stature accompanied with mental retardation, generalized hyperpigmentation of the skin and craniofacial findings. Her cardiological examination revealed atrial septal defect, mitral valve prolapsus and atrial septal aneurysm. Brain scans revealed dilatation of the third and lateral ventricles and a pontine cleft. Growth hormone (GH) deficiency was observed during the evaluation of GH/IGF-I axis. All the laboratory tests performed including metabolic screening, conventional karyotype and oligonucleotide array were normal. Mutation analysis of the C2ORF3 7 gene revealed no mutation. The clinical signs seen in this patient likely represent a new dysmorphological syndrome which has not been previously described.
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PMID:A new clinical presentation associated with pontine clefting, hyperpigmentation and short stature in addition to craniofacial, cardiac and developmental anomalies. 2287 88

The IGF system plays a critical role in all phases of human growth, including intrauterine, childhood and pubertal. The importance of IGF-I for both in utero as well as postnatal human growth is highlighted by rare human homozygous IGF1 mutations, which are characterized by intrauterine growth retardation (IUGR), microcephaly, mental retardation and severe postnatal growth failure. Clinical conditions of IGF-I resistance due to mutations in the IGF-I receptor (IGFIR) similarly lead to IUGR and postnatal growth retardation. Postnatal regulation of IGF-I production is predominantly GH dependent. Defects in the GH-IGF-I axis, including mutations in the GHR, STAT5B and IGFALS genes, lead to postnatal IGF deficiency and GH insensitivity. Patients are of normal birth size but present with severe postnatal growth failure, despite normal or elevated levels of GH. Other phenotypic features - immune deficiency for STAT5B defects and insulin insensitivity for IGFALS defects - are of note. Mutations identified have been predominantly recessive. The identification and assessment of genetic defects in the GH-IGF axis has greatly enhanced our understanding of the critical importance of IGF-I in human linear growth. Continued evaluations will facilitate better diagnosis and management of children presenting with abnormal growth and development.
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PMID:IGF-I in human growth: lessons from defects in the GH-IGF-I axis. 2350 38

Sensorineural hearing loss is a clinical heterogeneous disorder and a significant health-care problem with tremendous socio-economic impact. According to WHO, "Over 5% of the world's population has disabling hearing loss -328 million adults and 32 million children-". In children, early hearing loss affects language acquisition. Hearing deficits are generally associated with the loss of the sensory "hair" cells and/or neurons caused by primary genetic defects or secondary to environmental factors including infections, noise and ototoxic drugs. Hearing loss cannot be reversed and currently the available treatment is limited to hearing aids and cochlear implants. Studies are being conducted to develop alternative treatments combining both preventive and reparative strategies. Human insulin like growth factor (IGF) I deficiency is a rare disease associated with hearing loss, poor growth rates and mental retardation (ORPHA73272, OMIM608747). Similarly, lgf1-/- mice are dwarfs with poor survival rates and congenital profound sensorineural deafness. IGF-I is known to be a neuroprotective agent that maintains cellular metabolism, activates growth, proliferation and differentiation, and limits cell death. Here we will discuss the basic mechanisms underlying IGF-I actions in the auditory system and their clinical implications to pursue novel treatments to ameliorate hearing loss.
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PMID:IGF-I deficiency and hearing loss: molecular clues and clinical implications. 2395 97