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Query: UMLS:C0025362 (mental retardation)
 15,878 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Autosomal recessive primary microcephaly (MCPH) is a neurodevelopmental disorder. It is characterized by two principal features, microcephaly present at birth and nonprogressive mental retardation. The microcephaly is the consequence of a small but architecturally normal brain, and it is the cerebral cortex that shows the greatest size reduction. There are at least seven MCPH loci, and four of the genes have been identified: MCPH1, encoding Microcephalin; MCPH3, encoding CDK5RAP2; MCPH5, encoding ASPM; and MCPH6, encoding CENPJ. These findings are starting to have an impact on the clinical management of families affected with MCPH. Present data suggest that MCPH is the consequence of deficient neurogenesis within the neurogenic epithelium. Evolutionary interest in MCPH has been sparked by the suggestion that changes in the MCPH genes might also be responsible for the increase in brain size during human evolution. Indeed, evolutionary analyses of Microcephalin and ASPM reveal evidence for positive selection during human and great ape evolution. So an understanding of this rare genetic disorder may offer us significant insights into neurogenic mitosis and the evolution of the most striking differences between us and our closest living relatives: brain size and cognitive ability.
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PMID:Autosomal recessive primary microcephaly (MCPH): a review of clinical, molecular, and evolutionary findings. 1580 41

Using comparative sequencing approaches, we investigated the evolutionary history of the European-enriched 17q21.31 MAPT inversion polymorphism. We present a detailed, BAC-based sequence assembly of the inverted human H2 haplotype and compare it to the sequence structure and genetic variation of the corresponding 1.5-Mb region for the noninverted H1 human haplotype and that of chimpanzee and orangutan. We found that inversion of the MAPT region is similarly polymorphic in other great ape species, and we present evidence that the inversions occurred independently in chimpanzees and humans. In humans, the inversion breakpoints correspond to core duplications with the LRRC37 gene family. Our analysis favors the H2 configuration and sequence haplotype as the likely great ape and human ancestral state, with inversion recurrences during primate evolution. We show that the H2 architecture has evolved more extensive sequence homology, perhaps explaining its tendency to undergo microdeletion associated with mental retardation in European populations.
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PMID:Evolutionary toggling of the MAPT 17q21.31 inversion region. 1916 22

The plantar grasp reflex can be elicited in all normal infants from 25 weeks of postconceptional age until the end of 6 months of corrected age according to the expected birth date. This reflex in human infants can be regarded as a rudiment of responses that were once essential for ape infants in arboreal life. The spinal center for this reflex is probably located at the L(5)-S(2) levels, which, however, are controlled by higher brain structures. Nonprimary motor areas may exert regulatory control of the spinal reflex mechanism through interneurons. In infants, this reflex can be elicited as the result of insufficient control of the spinal mechanism by the immature brain. In adults, lesions in nonprimary motor areas may cause a release of inhibitory control by spinal interneurons, leading to a reappearance of the reflex. The plantar grasp reflex in infants is of high clinical significance. A negative or diminished reflex during early infancy is often a sensitive indicator of spasticity. Infants with athetoid type cerebral palsy exhibit an extremely strong retention of the reflex, and infants with mental retardation also exhibit a tendency toward prolonged retention of the reflex.
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PMID:Neural mechanism and clinical significance of the plantar grasp reflex in infants. 2061 Jan 16

Two consanguineous families with Uner Tan Syndrome (UTS) were analyzed in relation to self-organizing processes in complex systems, and the evolutionary emergence of human bipedalism. The cases had the key symptoms of previously reported cases of UTS, such as quadrupedalism, mental retardation, and dysarthric or no speech, but the new cases also exhibited infantile hypotonia and are designated UTS Type-II. There were 10 siblings in Branch I and 12 siblings in Branch II. Of these, there were seven cases exhibiting habitual quadrupedal locomotion (QL): four deceased and three living. The infantile hypotonia in the surviving cases gradually disappeared over a period of years, so that they could sit by about 10 years, crawl on hands and knees by about 12 years. They began walking on all fours around 14 years, habitually using QL. Neurological examinations showed normal tonus in their arms and legs, no Babinski sign, brisk tendon reflexes especially in the legs, and mild tremor. The patients could not walk in a straight line, but (except in one case) could stand up and maintain upright posture with truncal ataxia. Cerebello-vermial hypoplasia and mild gyral simplification were noted in their MRIs. The results of the genetic analysis were inconclusive: no genetic code could be identified as the triggering factor for the syndrome in these families. Instead, the extremely low socio-economic status of the patients was thought to play a role in the emergence of UTS, possibly by epigenetically changing the brain structure and function, with a consequent selection of ancestral neural networks for QL during locomotor development. It was suggested that UTS may be regarded as one of the unpredictable outcomes of self-organization within a complex system. It was also noted that the prominent feature of this syndrome, the diagonal-sequence habitual QL, generated an interference between ipsilateral hands and feet, as in non-human primates. It was suggested that this may have been the triggering factor for the attractor state "bipedal locomotion" (BL), which had visual and manual benefits for our ape-like ancestors, and therefore enhancing their chances for survival, with consequent developments in the psychomotor domain of humans. This was put forward as a novel theory of the evolution of BL in human beings.
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PMID:Two families with quadrupedalism, mental retardation, no speech, and infantile hypotonia (Uner Tan Syndrome Type-II); a novel theory for the evolutionary emergence of human bipedalism. 2479 58