Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0026827 (hypotonia)
 5,860 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Non-mosaic males with a 46,XY karyotype and a MECP2 null mutation display a phenotype of severe neonatal-onset encephalopathy that is distinctly different from Rett syndrome (RTT). To increase awareness of this rare disorder, we are reporting novel findings in a sporadic case, compare them to 16 previously reported cases and establish salient criteria for clinical diagnosis. The proband suffered from general hypotonia and hypoxia caused by hypoventilation and irregular breathing. He developed abnormal movements, seizures and electroencephalogram abnormalities. He failed to thrive and to reach any motor milestones and died at 15 months from central respiratory failure without a diagnosis. In a muscle biopsy, type II fibers were reduced in diameter, indicating central hypoxia. At autopsy, the brain was small with disproportionate reduction of the frontal and temporal lobes. Synaptophysin staining of synaptic vesicles was greatly reduced in cerebellar and spinal cord sections. Analysis of Golgi-stained pyramidal neurons from cortical layers III and V of the frontal and temporal lobes revealed drastically diminished dendritic trees. Post-mortem MECP2 mutation analysis on DNA and RNA from fibroblasts revealed a novel de novo 9-nucleotide deletion including the intron 3/exon 4 splice junction. The two nucleotides flanking the deletion form a new splice site, and the aberrantly spliced transcript lacks seven nucleotides (r.378_384delTCCCCAG), causing a frameshift and premature termination codon (p.I126fsX11). Males with congenital encephalopathy, not females with RTT, represent the true human counterpart for the commonly studied Mecp2-/y mouse model and provide unique insight into the mechanisms of MeCP2 deficiency.
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PMID:Severe congenital encephalopathy caused by MECP2 null mutations in males: central hypoxia and reduced neuronal dendritic structure. 1847

Following exocytosis, synaptic vesicles (SVs) have to be reformed with the correct complement of proteins in the correct stoichiometry to ensure continued neurotransmission. Synaptophysin is a highly abundant, integral SV protein necessary for the efficient retrieval of the SV SNARE protein, synaptobrevin II (sybII). However the molecular mechanism underpinning synaptophysin-dependent sybII retrieval is still unclear. We recently identified a male patient with severe intellectual disability, hypotonia, epilepsy and callosal agenesis who has a point mutation in the juxtamembrane region of the fourth transmembrane domain of synaptophysin (T198I). This mutation had no effect on the activity-dependent retrieval of synaptophysin that was tagged with the genetically-encoded pH-sensitive reporter (pHluorin) in synaptophysin knockout hippocampal cultures. This suggested the mutant has no global effect on SV endocytosis, which was confirmed when retrieval of a different SV cargo (the glutamate transporter vGLUT1) was examined. However neurons expressing this T198I mutant did display impaired activity-dependent sybII retrieval, similar to that observed in synaptophysin knockout neurons. Interestingly this impairment did not result in an increased stranding of sybII at the plasma membrane. Screening of known human synaptophysin mutations revealed a similar presynaptic phenotype between T198I and a mutation found in X-linked intellectual disability. Thus this novel human synaptophysin mutation has revealed that aberrant retrieval and increased plasma membrane localisation of SV cargo can be decoupled in human disease.
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PMID:Altered synaptobrevin-II trafficking in neurons expressing a synaptophysin mutation associated with a severe neurodevelopmental disorder. 2888 51