Mutation analysis of the TSC2 gene in an African-American family

Tuberous sclerosis complex is an autosomal dominant disorder with loci on chromosome 9q34 (TSC1) and chromosome 16p13.3 (TSC2). The TSC2 gene has been isolated. To date, only a small number of intragenic deletional and point mutations have been detected, almost exclusively in sporadic (no family history) cases. With the exception of a single parent/offspring pair, there have been no published reports of mutations in extended multigenerational chromosome 16-linked TSC2 families. For our TSC studies we ascertained and sampled a four-generation African-American TSC family that shows a high likelihood for linkage to chromosome 16 (z=1.53). Using single-strand conformation polymorphism analysis we identified a 4590/4591delC mutation in exon 34. The 4590/4591delC causes a frameshift mutation resulting in the creation of a premature stop codon. In addition, we have detected a 542del4 polymorphism in the two partially overlapping polyadenylation signals in exon 40 that segregates in the family. The polymorphism has been detected in six of 72 African-American control chromosomes examined, and has not been detected in 80 Caucasian control chromosomes examined.     

Schwann cells proliferate at rat neuromuscular junctions during development and regeneration

Terminal Schwann cells (TSCs) cover neuromuscular junctions and are important in the repair and maintenance of these synapses. We have examined how these cells are generated at developing junctions and how their number is regulated during repair of nerve injury. At birth, approximately half of the junctions in rat soleus and extensor digitorum longus muscles have one TSC soma. Somata are absent from the remainder, although Schwann cell (SC) processes arising from somata along the preterminal axon cover almost all of these synapses. By 2 months of age, junctions have gained an additional two to three TSCs. Most of this gain occurs during the first 2 postnatal weeks and largely precedes the expansion of endplate size. Although the initial addition is caused by cell migration, mitotic labeling shows extensive division of TSCs at junctions. A slower addition of TSCs occurs in adult muscles, and TSC number in the adult is correlated with endplate size. During repair of nerve injury, TSC number is regulated by a combination of signals from motor neurons and denervated tissue. As shown previously (Connor et al., 1987), denervation of adult muscles did not, in itself, cause TSC mitosis. However, TSCs became mitotic during reinnervation. Partial denervation induced division of TSCs at innervated but not denervated endplates. A disproportionate number of these mitotic cells were found at endplates contacted by TSC processes extended from nearby denervated endplates, contacts known to promote nerve sprouting. These results show an association between TSC mitotic activity and alterations in synaptic structure during development, sprouting, and reinnervation.     

Inactivation of the cyclin-dependent kinase inhibitor p27 upon loss of the tuberous sclerosis complex gene-2

Tuberous sclerosis is an autosomal dominant disorder characterized by the development of aberrant growths in many tissues and organs. Linkage analysis revealed two disease-determining genes on chromosome 9 and chromosome 16. The tuberous sclerosis complex gene-2 (TSC2) on chromosome 16 encodes the tumor suppressor protein tuberin. We have shown earlier that loss of TSC2 is sufficient to induce quiescent cells to enter the cell cycle. Here we show that TSC2-negative fibroblasts exhibit a shortened G1 phase. Although the expression of cyclin E, cyclin A, p21, or Cdc25A is unaffected, TSC2-negative cells express much lower amounts of the cyclin-dependent kinase (CDK) inhibitor p27 because of decreased protein stability. In TSC2 mutant cells the amount of p27 bound to CDK2 is diminished, accompanied with elevated kinase activity. Ectopic expression studies revealed that the aforementioned effects can be reverted by transfecting TSC2 in TSC2-negative cells. High ectopic levels of p27 have cell cycle inhibitory effects in TSC2-positive cells but not in TSC2-negative counterparts, although the latter still depend on CDK2 activity. Loss of TSC2 induces soft agar growth of fibroblasts, a process that cannot be inhibited by high levels of p27. Both phenotypes of TSC2-negative cells, their resistance to the activity of ectopic p27, and the instability of endogenous p27, could be explained by our observation that the nucleoprotein p27 is mislocated into the cytoplasm upon loss of TSC2. These findings provide insights into the molecular mechanism of how loss of TSC2 induces cell cycle entry and allow a better understanding of its tumor suppressor function.     

"Ideal" length of stay after colectomy: whose ideal?

The tuberous sclerosis 2 (TSC2) gene is thought to function as a growth suppressor in sporadic and TSC-associated hamartomas and tumors. Clusters of dysplastic glial cells are a common feature of cortical tubers and subependymal nodules in tuberous sclerosis patients. In an effort to identify TSC2 gene alterations in sporadic gliomas, we detected a novel polymorphism adjacent to the 3'splice site of intron 4. We evaluated the distribution of this variant allele in a series of 244 patients with glial tumors, including 55 gangliogliomas, 31 pilocytic astrocytomas (WHO grade I), 50 astrocytomas (WHO grades II and III), and 108 glioblastomas (WHO grade IV). The allelic distribution in the general population was estimated by examining 381 healthy blood donors. This rare allele appeared in the control population and in the patients with astrocytic gliomas with a virtually identical frequency (8.14%, and 8.20%, respectively). The frequency of the rare allele in gangliogliomas, however, was significantly higher (15.5%; p = 0.024). The fact that both gangliogliomas and cortical tubers in tuberous sclerosis contain neuronal and astrocytic elements and may resemble each other histologically suggests that the TSC2 gene may be involved in the development of these tumors. The rare allele of the TSC2 gene emerges as a candidate for a predisposing factor for the formation of sporadic gangliogliomas.     

Constancy of absolute judgments of size by normals and schizophrenics.

A study of size constancy in absolute judgments of chronic schizophrenics and normals under conditions of minimal distance cues showed a significant and consistent underestimation by schizophrenic Ss. The apparently inconsistent results from other studies of size and temporal constancy in schizophrenics were discussed and a hypothesis advanced which related the various findings as a function of loss of reality contact. Schizophrenics in good contact show stable overconstancy. Acutely disturbed schizophrenics show a loss of perceptual stability. Chronic schizophrenics have re-established perceptual stability through autistic frames of reference. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of weight intensity on discrimination thresholds of normals and schizophrenics.

20 male chronic schizophrenics, 12 chronic disturbed schizophrenics, and 20 normal controls were tested for upper difference limens from both a 40-gm (light) and 400-gm (heavy) standard weight. Weight discrimination thresholds were found to be significantly elevated as a function of severity of pathology in the schizophrenic groups and also at the lighter weight intensity. Both groups of schizophrenics showed significantly greater improvement than normals with the heavy weights. The less disturbed chronic schizophrenics were not significantly different from normals at the heavy intensity. The results support the hypothesis of a schizophrenic deficit in proprioceptive acuity and suggest that this deficit is the result of insufficient proprioceptive feedback. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An event-related brain potential substrate of disturbed response monitoring in paranoid schizophrenic patients.

Response monitoring in schizophrenic patients and healthy controls was assessed by measuring performance and event-related brain potentials in the flanker priming task. Three visual-context conditions were construed: Flankers and targets pointed either into the same direction or into different directions. Stimuli without any response assignment were used as flankers in the neutral context condition. The schizophrenic patients were further subdivided into paranoid (n?=?19) and nonparanoid (n?=?10) patients and compared with healthy controls (n?=?18). Performance scores revealed that the flankers induced a similar degree of distraction by visual context in all 3 groups. Although the schizophrenic patients showed normal error correction performance, the error negativity (NE) was significantly reduced in paranoid schizophrenic patients. The attenuation of the NE possibly reflects disturbed response monitoring in these patients. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Psychological evaluation of clinical disturbance in children at risk for psychopathology.

Evaluated children of 1 schizophrenic or 1 manic-depressive parent for clinical disturbance in the St. Louis risk research project between 1967 and 1971. The investigation employed a psychological battery using the WISC or WAIS, figure drawings, the TAT, the Rorschach, and the Beery-Buktenica Developmental Form Sequence, plus blind clinical disturbance ratings from the test batteries. Tests were administered individually to 339 6–20 yr old children from intact families with 1 schizophrenic, manic-depressive, or physically ill parent, or 2 normal parents. Children of psychiatrically ill parents were found to be more disturbed than children of nonpsychotic parents. Children with a schizophrenic parent demonstrated peformance on psychometric evaluation that was in some ways continuous with that of adult schizophrenics. Children of schizophrenic and manic-depressive parents differed from one another and from controls on 2 measures. In the aggressive content of their TAT stories, children with a schizophrenic parent showed less aggression than normals, and children with a manic-depressive parent showed more aggression than normals. On the Rorschach, children of schizophrenics gave more primitive responses than children of manic-depressives, and the children of normal parents gave an intermediate number of such responses. (2 p ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cytoarchitecture of the entorhinal cortex in schizophrenia

OBJECTIVE: The purpose of this study was to determine whether schizophrenia is associated with abnormalities in neuronal migration in the entorhinal cortex. METHOD: Nissl-stained sections through three cytoarchitectonic subdivisions of the entorhinal cortex were examined in postmortem brain specimens from 10 schizophrenic subjects and 10 matched normal comparison subjects. RESULTS: No qualitative differences in cytoarchitecture were observed between the schizophrenic and comparison subjects. CONCLUSIONS: These findings do not replicate previous reports of cytoarchitectural disturbances in the entorhinal cortex of schizophrenic subjects and thus fail to support the hypothesis of abnormal neuronal migration in schizophrenia.     

Sex-role development and psychopathology in adult males.

Compared the responses of matched groups of 20 nonparanoid schizophrenic, paranoid schizophrenic, neurotic, and normal adult males on measures relating to masculinity-femininity of self-perceptions (Adject Check List) and interests and attitudes (the Femininity scale of the CPI). Results consistently indicate that all the disturbed groups were much less masculine than the normal Ss. There were few clear-cut differences among the disturbed groups. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analysis of a structural polymorphism in the 5-HT2A receptor and clinical response to clozapine

Clozapine is an atypical antipsychotic with affinity for a broad range of receptors, including serotonin (5-HT) and dopamine receptors. It is successful in treating about 60% of patients refractory to other antipsychotic drugs. Since genetic variation in clozapine's neurotransmitter receptor targets may affect clinical response through altering drug binding or receptor expression, we have studied a His452Tyr polymorphism in the 5-HT2A receptor (HTR2A) in a sample of 153 schizophrenic patients undergoing clozapine treatment and 178 normal controls. An association was found between the allele Tyr452 and poor clinical response.     

Schizophrenia as a "put-on."

Refutes findings of L. S. Levitz and L. P. Ullman (see43:4) by citing evidence that schizophrenics are unresponsive to social instructions and verbal reinforcement, and differ from normals in being unable to turn off disturbed thinking. The importance of determining reinforcement contingencies and the mechanisms responsible for schizophrenic thinking in order to modify central schizophrenic symptoms is emphasized. (25 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrophoretic pattern of red blood cell catechol-o-methyltransferase in schizophrenia and manic-depressive illness

Human red blood cell (RBC) catechol-O-methyltransferase (COMT) was analyzed by polyacrylamide gel electrophoresis (PAGE). One major enzyme band (B) is observed after electrophoresis. In addition, a minor band (A) of COMT activity comprising no more than 25% of the total activity, is also detectable. The rate of migration during electrophoresis of both bands of RBC COMT was the same in manic depressive, schizophrenic, and normal individuals. These results did not reveal genetic variations in the COMT molecule among these three groups. Furthermore, when total RBC COMT was measured there were no statistically significant differences between schizophrenic, manic-depressive, and control individuals.     

Loss of heterozygosity in tuberous sclerosis hamartomas

We have previously described in tuberous sclerosis (TSC) hamartomas the phenomenon of loss of heterozygosity (LOH) for DNA markers in the region of both the TSC2 gene on chromosome 16p13.3 and the TSC1 gene on 9q34. We now describe the spectrum of LOH in 51 TSC hamartomas from 34 cases of TSC. DNA was extracted from leucocytes or normal paraffin embedded tissue, and from frozen paraffin embedded hamartoma tissue from the same patient. The samples were analysed for 11 markers spanning the TSC1 locus and nine markers spanning the TSC2 locus. Twenty-one of 51 hamartomas showed LOH (41%). There was significantly more LOH on 16p13.3, with 16 hamartomas showing LOH around TSC2, and five in the vicinity of TSC1. No hamartoma showed LOH for markers around both loci. All the areas of LOH on chromosome 9 were large, but the smallest region of overlap lay between the markers D9S149 and D9S114, providing independent evidence for the localisation of the TSC1 gene. These data show that LOH is a common finding in a wide range of hamartomas, affecting the same TSC locus in different lesions from the same patient but not affecting both loci. These data support the hypothesis that both the TSC genes act as tumour suppressors and that the manifestations of TSC in patients with germline TSC mutations rise from "second hit" somatic mutations inactivating the remaining normal copy of the TSC gene.     

Red cell membrane fatty acids, cytosolic phospholipase-A2 and schizophrenia

Forty subjects with schizophrenia and 40 age- and sex-matched controls were recruited, and blood samples were obtained for analysis of red cell membrane fatty acid composition by capillary gas chromatography. A blood sample was also taken from the same population to test for allelic association between schizophrenia and a polymorphism close to the promoter site of the cytosolic phospholipase-A2 gene which is mapped to chromosome 1q25. The schizophrenic population was heterogeneous with regards age, symptoms severity and treatment. A significantly higher percentage concentration of dihomogamma-linolenic acid (DGLA) was found in the red cell membranes of schizophrenics compared to matched controls. All other fatty acids examined showed no difference from the normal population. No correlation was found between any demographic factor, treatment variable, diet, drug use, alcohol or tobacco consumption which could explain the biochemical findings. A negative correlation was found between the concentration of DGLA in red blood cell (RBC) membranes and severity of symptoms of schizophrenia. In particular, there was a significant correlation (r = -0.41, p = 0.009) between DGLA percentage concentrations and 'disorganised' symptoms. No association was found between schizophrenia and alleles of the polymorphism near the phospholipase-A2 gene or between fatty acid concentrations and the presence of any particular alleles. This study therefore finds support for membrane phospholipid abnormalities in patients with schizophrenia and particular symptom clusters, but does not replicate a previous report of an allelic association between a polymorphism close to the site of the cytosolic phospholipase-A2 gene and schizophrenia.     

Study of the viscosity of excited membranes using combined dispersion spectroscopy

Tuberous sclerosis (TSC) is an autosomal dominant disorder characterized by seizures, mental retardation, and hamartomatous lesions. Although hamartomas can occur in almost any organ, they are most common in the brain, kidney, heart, and skin. Allelic loss or loss of heterozygosity (LOH) in TSC lesions has previously been reported on chromosomes 16p13 and 9q34, the locations of the TSC2 and TSC1 genes, respectively, suggesting that the TSC genes act as tumor-suppressor genes. In our study, 87 lesions from 47 TSC patients were analyzed for LOH in the TSC1 and TSC2 chromosomal regions. Three findings resulted from this analysis. First, we confirmed that the TSC1 critical region is distal to D9S149. Second, we found LOH more frequently on chromosome 16p13 than on 9q34. Of the 28 patients with angiomyolipomas or rhabdomyomas, 16p13 LOH was detected in lesions from 12 (57%) of 21 informative patients, while 9q34 LOH was detected in lesions from only 1 patient (4%). This could indicate that TSC2 tumors are more likely than TSC1 tumors to require surgical resection or that TSC2 is more common than TSC1 in our patient population. It is also possible that small regions of 9q34 LOH were missed. Lastly, LOH was found in 56% of renal angiomyolipomas and cardiac rhabdomyormas but in only 4% of TSC brain lesions. This suggests that brain lesions can result from different pathogenic mechanisms than kidney and heart lesions.