Ultrastructural studies of concanavalin A receptors and 5′-nucleotidase localization in normal and injured mouse cerebral microvasculature

Summary Plant lectin concanavalin A conjugated with ferritin (Con A-F) injected i.v. was used for the detection of the specific monosaccharide residues (-d-mannosyl and -d-glucosyl) on the luminal surface of endothelial cells (ECs) in brain micro-blood vessels (MBVs). Both normal mice and animals with mechanically damaged blood-brain barrier (BBB) were used in this study. In addition, the activity of 5-nucleotidase (5N), the putative receptor for Con A, was studied cytochemically.Various methodologic experiments indicated that the reaction product formed on the luminal plasmalemma of ECs after incubation of samples in the cytochemical medium for the detection of 5N activity results from the action of unspecific phosphatase hydrolyzing both specific and nonspecific substrates. The abluminal side of the wall of MBVs seems to be a major location of 5N activity. Thus, no correlation between cytochemically demonstrable 5N activity and Con A receptor sites on the luminal surface of ECs was noted.After damage of the BBB, extensive internalization of the luminal plasmalemma forming the limiting membranes of pinocytotic vesicles, vacuoles, and endothelial channel-like structures was observed. This process was represented by a relatively rapid translocation of Con A receptors from luminal surface into the interior of the ECs and to the abluminal side of the vessel wall.Abbreviations AP Alkaline phosphatase - 5N 5-nucleotidase phate - AMP adenosine 5-monophosphate - CMP cytidine 5-monophosphate - GMP guanosine 5-monophosphate - UMP uridine 5-monophosphate - Con A concanavalin A - BBB blood-brain barrier - EC endothelial cell - HRP horseradish peroxidase - MBVs micro-blood vessels - NDPase nucleoside diphosphatase Supported in part by a grant from NINCDS No.17271-03     

Liquorkomplement und Multiple Sklerose

Zusammenfassung 1. In 239 Liquores, darunter 47 MS-Fälle und 91 normale Kontrollen, wurden Komplement und Komplementfaktoren (C₁, C₂, C₃ und C₄) bestimmt.2. Im normalen Liquor ist in der Regel keine Gesamtkomplementaktivität vorhanden. Dagegen ist die C₁- wie C₄-Aktivität praktisch immer und C₂-sowie C₃-Aktivität in über der Hälfte der Fälle zu finden. Das Komplementmuster im Liquor ist daher im Gegensatz zum Serum unvollständig.3. Bei erhöhtem Eiweiß zeigt der Liquor dagegen häufig Gesamtkomplementaktivität. Je höher das Liquoreiweiß ist, um so höher ist der Gehalt an C₂, C₃ und Gesamtkomplement. Diese Beziehungen zwischen Gesamteiweiß und Komplementaktivität gelten für normalen wie pathologischen Liquor einschließlich der MS-Fälle.4. Im MS-Liquor sind C₂, C₃ und Gesamtkomplement seltener zu finden als bei den Kontrollen. Bei den MS-Patienten ist C₂ und C₃ im akuten Schub herabgesetzt. C₃ nimmt im Verlauf der Erkrankung wahrscheinlich ab.5. Mit Antikomplementserum wurde _1C-Globulin, ein Teilfaktor von C₃, im Liquor von 55 MS-Patienten und 42 Kontrollen bestimmt. Es besteht kein Unterschied zwischen MS und Kontrolliquor. Auch bei akut entzündlicher MS ist _1C nicht vermindert.6. In der Diskussion wird auf widersprechende eigene Befunde über _1C-Inaktivierung im Serum während der akut entzündlichen MS-Phase hingewiesen.

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Summary 1. Complement and complement factors (C₁, C₂, C₃ and C₄) were determined in 239 specimes of cerebrospinal fluid (CSF) including 47 cases of Multiple Sclerosis (MS) and 91 normal controls.2. In general, total complement activity is absent in normal specimens while that of C₁ and C₄ can be found practically always and that of C₂ and C₃ in more than half of the cases. Therefore, the pattern of complements in the CSF is incomplete as opposed to that of serum.3. In contrast, samples with increased protein content frequently yield total complement activity. The higher the protein content of CSF the higher the content of C₂, C₃ and total complement. This relationship between amount of total protein and complement activity applies both to normal and pathological CSF specimens including those from MS.4. In cerebrospinal fluid from patients with MS, C₂, C₃ and total complement are found less frequently than in that from controls. C₂ and C₃ are diminished in patients with an acute exacerbation of MS. C₃ decreases probably in the course of the disease.5. _1C-globulin, a component of C₃, was determined with anticomplement sera in specimens from 55 patients with MS and from 42 controls. There is no difference between CSF of MS and controls. Even in acutely inflammatory cases of MS, _1C is not diminished.6. Discussing his results the author points out discrepancies concerning the nactivation of _1C in serum during acutely inflammatory episodes of MS.

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Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

In situ hybridization with digoxigenin-labeled probes: sensitive and reliable detection method applied to myelinating rat brain

Summary A method for in situ hybridization of digoxigenin-labeled cDNA and cRNA probes to myelin protein mRNA is described. This technique has dual advantages of high structural resolution and high sensitivity and avoids problems associated with handling of radioactive materials. Furthermore, it can be readily combined in double labeling with immunocytochemical protein detection. We have used this technique to detect and locate mRNA for myelin basic protein (MBP), proteolipid protein (PLP), 2,3-cyclic nucleotide 3-phosphodiesterase (CNPase) and myelin-associated glycoprotein (MAG) in oligodendrocytes of 7-day-old and adult rat brains. PLP and MAG mRNA were restricted to the perinuclear cytoplasm, whereas MBP and CNPase mRNA was additionally present in peripheral oligodendrocyte processes.Supported by the Science Research Fund, Austria, P 7740M     

Dysbalance of neuronal second messenger function in the aetiology of affective disorders: A pathophysiological concept hypothesising defects beyond first messenger receptors

Summary It is suggested that affective disorders arise from the dysbalance of the two major intraneuronal signal amplification systems, the adenylate cyclase and the phospholipase C system, with depression resulting from underfunction of cyclic adenosine 3,5-monophosphate-mediated effector cell responses associated with an absolute or relative dominance of the inositoltriphosphate/ diacylglycerol-mediated responses and mania resulting from the converse. The usefulness of this hypothesis is discussed with respect to (a) the mechanism of action of current therapeutic agents and (b) the development of novel therapeutic approaches.     

Heterologous supersensitization between serotonin2 and alpha2-adrenergic receptor-mediated intracellular calcium mobilization in human platelets

Summary Recent reports suggest that serotonin (5-HT)₂ receptor-mediated second messenger systems are enhanced in platelets of affective disorders. To make the mechanism of the enhanced response clear, we investigated 5-HT₂ and alpha ()₂-adrenergic receptor-induced intracellular calcium (Ca²⁺) mobilization in platelets of healthy volunteers, using fura-2. 5-HT₂ and ₂-adrenergic receptor-mediated Ca²⁺ mobilization was enhanced by prior exposure to the other type of agonist, so called heterologous supersensitization. The supersensitization was due to the enhancement of maximal response without change in agonist affinity. Chelating extracellular Ca²⁺ did not diminish the supersensitization. This enhancement of Ca²⁺ mobilization was not inhibited by H-7, an inhibitor of protein kinase C. However, this supersensitization was inhibited by pretreatment with sodium fluoride which directly activates guanine nucleotide binding regulatory proteins (G proteins). These results suggest that the supersensitization was caused from intracellular Ca²⁺ storage sites through a G protein-coupled pathway.Abbreviations fura-2/AM 1-(2-(5-carboxyoxazol-2-yl)-6-aminobenzofuran-5-oxy)-2-(2-amino-5-methylphenoxy)-ethane-N,N,N, N-tetraacetic acid, pentaacetoxymethyl ester - H-7 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride - EGTA ethylenedioxybis(ethylamine)-N,N,N,N-tetraacetic acid - HEPES 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - NaF sodium fluoride - Fmax maximal fluorescence intensity - Fmin minimal fluorescence intensity     

Association analysis of a neural nitric oxide synthase gene polymorphism and antipsychotics-induced tardive dyskinesia in Chinese schizophrenic patients

Summary. Recent findings from rodent studies with chronic administration of antipsychotic drugs have indicated the role of neural nitric oxide synthase (NOS1) on the susceptibility of tardive dyskinesia (TD). In the present study, the association between a 3-untranslated region C267T (3-UTR C267T) polymorphism of the NOS1 gene and TD as well as TD severity was investigated in 251 Chinese schizophrenic patients with long-term antipsychotic treatment (TD: 128, non-TD: 123). After adjusting the effects of confounding factors, there was no significant association between NOS1 3-UTR C276T genotypes and TD occurrence (p=0.758). With in the TD group, we could not discover a significant correlation between NOS1 3-UTR C276T genotypes and the scores of abnormal involuntary movement scale (AIMS) (p=0.219 and 0.774). We concluded that the NOS1 3-UTR C276T polymorphism might not play a major role in the susceptibility of TD development, or on the severity of TD.     

Human glial fibrillary acidic protein (GFAP): molecular cloning of the complete cDNA sequence and chromosomal localization (chromosome 17) of the GFAP gene

Summary We isolated three glial fibrillary acidic protein (GFAP) cDNA clones from a glioma cell line, U-251 MG. One clone isolated from a U-251 MG cDNA library was long, but lacked both ends. Using poly(A)⁺ RNA and primers synthesized according to the sequence of this clone, we used the polymerase chain reaction-assisted rapid amplification of cDNA ends (PCR-RACE) method, which is a strategy to isolate cDNA ends, and obtained cDNA clones for the 5 and 3 ends. From the sequences of these overlapping clones, the complete nucleotide sequence of human GFAP cDNA was established. The start (ATG) and the stop (TGA) signals were seen at nucleotide positions 15 and 1311, respectively, and divided the entire sequence of 3027 bp into 14 bp of 5 non-coding, 1296 bp of coding and 1717 bp of 3 non-coding regions. Using cDNA probes made from both the coding and the 3 non-coding regions, Northern blot hybridization was performed with two different stringencies on RNAs from human and rodent brains and human GFAP-positive and-negative cells. It was shown that the 3 non-coding region probe was more specific for human GFAP than the coding region probe which was specific only under higher stringency conditions. This was also suggested by homology analysis of the sequence with those of various intermediate filament proteins. Based on these findings, we performed spot blot hybridization of sorted human chromosomes and Southern blot hybridization of PCR-amplified DNAs of a panel of hamster-human somatic cell hybrids and localized the human GFAP gene to chromosome 17.     

Human acoustic neurinomas: Nervous system specific biochemical parameters

Summary A series of 24 human acoustic neurinomas from 24 patients has been assayed for several biochemical parameters characteristic of the nervous system. S 100 protein, 2, 3-cyclic nucleotide 3-phosphohydrolase activity, and the myelin lipids galactosylceramide and sulfogalactosylceramide (sulfatide). Myelin basic protein was not detected. These findings further support the neuroectodermal origin of the human acoustic neurinoma, and provide additional biochemical markers for further study.     

Comparison of the active standing test and head-up tilt test for diagnosis of syncope in childhood and adolescence

Abstract We examined 51 children and adolescents with orthostatic symptoms using two orthostatic tests, the active standing test (the AS test) and head-up tilt test (HUT), and compared circulatory responses, autonomic function in addition to the induction rate of syncope during short-time orthostasis. Syncope was induced in eight patients with both tests, in only six patients with the AS test and in only one patient with HUT. The induction rate was significantly higher with the AS test (p<0.0001). In addition, the AS test is common and daily postural motion and does not require a tilt table. We calculated percent changes in systolic blood pressure at the initial drop (ID-SBP), in systolic blood pressure (SBP), in diastolic blood pressure (DBP), in heart rate (HR), component coefficient variation LF/HF (LF/HF) from supine to upright. HR were significantly larger in fainters than in non-fainters with both tests, although there was no difference in SBP and in DBP. In six fainters only with the AS test, HR was significantly larger with the AS test than with HUT. With the AS test ID-SBP were correlative with LF/HF, and LF/HF were correlative with HR, whereas these relations were not clear in HUT. These results indicated the AS test caused cardiac sympathetic activation associated with an initial pressure drop, and was more prone to induce syncope with a greater HR increase in some patients. We conclude the AS test is as potential as HUT as a diagnostic test for syncope.     

Autonomic neuropathy in patients with HIV: Course, impact of disease stage, and medication

The purpose of this article is to examine the prevalence, degree, and natural course of pupillary neuropathy (PANP), cardiovascular autonomic neuropathy (CANP), and sensorimotor neuropathy (SNP) and to study the impact of disease stage and medication on neuropathy in 61 consecutive patients with HIV. PANP, CANP, and SNP were assessed by standardized test procedures. Overall prevalence of PANP, CANP, and SNP were 66%, 15%, and 15%, respectively. The maximal pupillary area (pupillary measure, p<0.0001) and the lying-to-standing ratio (cardiovascular measure, p<0.0001) were abnormal as compared with control subjects. The changes in CD4+ T-lymphocytes and respiratory sinus arrhythmia percentile during 2 years of follow-up correlated significantly (r=0.758, p=0.007). Patients with CANP were more often in an advanced disease stage than patients without CANP (p=0.004). SNP, but not PANP or CANP, was associated with the intake of the neuropathogenic drugs dideoxycytidine, dideoxyinosine, and 2,3 didehydro-2,3 dideoxythymidine (p<0.05). Autonomic and sensorimotor neuropathy are frequent in patients with HIV, and progression of CANP may put patients at risk for unexpected cardiorespiratory arrest.     

Life events and syndromes of depression in the general population

Summary Brown and Harris (1978) contend that life events have causal significance for both psychotic and neurotic depression. This contradicts the psychiatric tradition. Neurotic depression has been regarded as a consequence of life-stress, while psychotic depression has been regarded as a consequence of processes intrinsic to the organism. Empirical evidence is presented to support the view that life events have a differential effect, within the general population. It is argued that Brown and Harris's (1978) conclusion follows from an inappropriate approach to classification. It is argued further that their data lend support to the traditional view. It is noted that their approach may inhibit the development of explanatory models linking life-stress, vulnerability factors and depression.     

S-100 protein and 2′,3′-cyclic nucleotide 3′-phosphohydrolase in human brain tumors

Summary Biopsy specimens from 23 human brain tumors have been analyzed for the nervous system specific protein S-100 and the membrane-associated enzyme 2,3-cyclic nucleotide 3-phosphohydrolase (CpNase). Biopsy specimens from an additional seven brain tumors were tested for either S-100 or CpNase alone.All astrocytomas and glioblastomas tested were found to contain S-100 and CpNase although there does not appear to be a strong correlation between the levels of these two markers in the 14 such tumors assayed for both. S-100 levels varied over a 19-fold range while CpNase varied over a 835-fold range. Postoperative survival in the astrocytoma and glioblastoma patients showed only a weak correlation with either tumor CpNase or S-100 levels.Two acoustic neurinomas, two oligodendrogliomas, one mixed glioma, and one choroid plexus papilloma were also assayed and found to have detectable levels of both S-100 and CpNase with the acoustic neurinomas and the mixed glioma having relatively high levels of each marker. All six meningiomas tested had low levels of CpNase. S-100 assays in three benign meningiomas were negative, while low levels of this protein were found in the one malignant meningioma tested.Tissue cultures were grown out from biopsy specimens of additional human brain tumors and tested at confluency for S-100. Of 15 astrocytoma and glioblastoma cultures tested, three had easily detectable amounts of S-100, two appeared to contain trace levels and ten were negative. The two acoustic neurinoma cultures tested were positive for S-100 while all three oligodendroglioma cultures were negative.     

Induction of glutathione S-transferase,placental type in T9 glioma cells by dibutyryladenosine 3′,5′-cyclic monophosphate and modification of its expression by naturally occurring isothiocyanates

Summary The effect of dibutyryladenosine 3,5-cyclic monophosphate (dibutyryl cAMP) on the expression of glutathione S-transferase placental type (GST-P) was examined in rat glioma cell line using an immunohistochemical technique. Cultured T9 glioma cells were negative for GST-P activity under normal conditions. However, treatment with 1 mM dibutyryl cAMP produced GST-P expression in about 50% of the cells, as well as some morphological changes. The expression of GST-P was increased with addition of dibutyryl cAMP together with 1 g/ml allyl isothiocyanate (AITC) or 0.1 g/ml benzyl isothiocyanate (BITC). With these combinated treatments, almost all cultured cells showed a strong positive reaction for GST-P, although AITC or BITC alone elicited GST-P in only 5% of the cultured cells. The results of the present study indicate that dibutyryl cAMP causes functional as well as morphological differentiation of T9 glioma cells.     

Isolation of a cDNA encoding the human brain serotonin transporter

Summary A cDNA encoding a serotonin transporter (5-HTT) in the human dorsal raphe nucleus was isolated and sequenced using cross-species amplification of human 5-HTT partial cDNA by the polymerase chain reaction (PCR) and the RACE-PCR procedure, designed for rapid amplification of 3 and 5 cDNA ends. The cDNA contains an open reading frame encoding a hydrophobic polypeptide of 630 amino acids with a calculated molecular weight of 70 kDa. The human 5-HTT is 92% homologous to the rat protein but contains an additional consensus phosphorylation site for cAMP-dependent protein kinase recognition located in the cytoplasmic N-terminal region, while a potential protein kinase C phosphorylation site identified in the rat homolog is not conserved in the human 5-HTT. Hydropathicity analysis revealed twelve membrane spanning segments, a topology proposed for other cloned sodium-dependent transporters.     

Autoradiographic studies of protein turnover in motoneurons of IDPN-treated rats

Summary Autoradiography was performed in order to envisage the turnover of H³-leucin labeled protein in the perikarya of spinal motoneurons and in the axonal balloons formed after repeated administrations of IDPN (--iminodiproprionitrile) in rats.These results suggested that (1) there was no significant, if any,in situ protein synthesis within the axon balloons, (2) the protein turnover was not appreciably altered in the perikarya of the control and IDPN-intoxicated rats, and (3) the labeled protein collected in the axon balloons seemed to be transported from the perikarya to which they were linked with short axonal segments (30 in average length).Supported in part by U.S. NIH Institutional Research Grant (and Neurology Foundation).     

Measles antibodies and κ-λ light chain distribution in immunoglobulins of patients affected with multiple sclerosis

Summary The presence of measles antibodies in serum immunoglobulin G fractions from seven patients affected with multiple sclerosis was investigated with the HI technic. The - light chain ratios of all samples under investigation were evaluated. Three multiple sclerosis patients, who displayed either fractionation or a tendency towards fractionation in their serum, had slightly elevated measles antibody titers associated to increased / ratios.

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Zusammenfassung Masern-Antikörper in Immunoglobulin-G-Fraktionen aus Seren von sieben Patienten mit Multipler Sklerose wurden mit der HI-Technik untersucht. Die Relation von leichter zu leichter wurde berechnet. Drei Multiple-Sklerose-Patienten, die entweder Immunoglobulin-Unterfraktionen oder eine Tendenz zu Unterfraktionen in ihren Seren aufwiesen, hatten eine leicht erhöhte Masern-Antikörper-Aktivität zugleich mit erhöhter /.

     

A 3’-UTR polymorphism in the oxidized LDL receptor 1 gene increases Aβ40 load as cerebral amyloid angiopathy in Alzheimer’s disease

It is presently unclear whether polymorphic variations in the oxidized low-density lipoprotein receptor 1 (OLR1), or low-density lipoprotein receptor-related protein 1 (LRP1), genes act as risk factors for Alzheimers disease (AD). In the present study, we have investigated the extent of amyloid protein (A) deposition as cerebral amyloid angiopathy (CAA) or senile plaques (SP) in relationship to OLR1 +1071 and +1073 polymorphisms and LRP1 C766T polymorphism in patients with AD There was an increased A₄₀ load as CAA, but not as SP, in frontal cortex of AD patients carrying OLR1+1073 CC genotype, compared to those with CT, TT or CT+TT genotypes, but only in those individuals without apolipoprotein (APOE) 4 allele. No differences in total A or A₄₂ load as CAA or SP between OLR1+1073 genotypes was seen, nor were there any differences between OLR1+1071 and LRP1 genotypes for any measure of A. Present data suggests that homozygosity for the C allele for OLR1+1073 polymorphism, selectively in individuals without APOE 4 allele, may impair clearance of A, and particularly A₄₀, from the brain across the blood-brain barrier, leading to its diversion into perivascular drainage channels, thereby increasing the severity of CAA in such persons.     

Dose-dependent pharmacokinetics of α-methyl-p-tyrosine (α-MT) and comparison of catecholamine turnover rates after two doses of α-MT

Summary Groups of rats were injected i.p. with 0.407 or 1.02 mmoles/kg of D, L--methyl-p-tyrosine methylester HCl (-MT). The time-courses for-MT in plasma and brain were followed together with the endogenous brain dopamine (DA) and noradrenaline (NA) contents.The elimination of-MT from plasma and brain was markedly delayed after the high-MT dose compared with the low dose. At 40 hours after the injection of 1.02 mmoles/kg of-MT both plasma and brain levels were high, whereas no-MT could be detected in plasma or brain at 16 hours after the lower dose.The brain catecholamines were decreased to very low values after the higher-MT dose (DA 14% and NA 10% of controls at 8 and 24 hours respectively). There was no complete recuperation at 40 hours of any of the amines. After the lower-MT dose, the DA concentration was back to control levels at 16 hours and NA at 12 hours. Between 16–40 hours after the high-MT dose a majority of the rats showed prominent signs of sedation, weight loss and dehydration. No such signs were observed in rats receiving 0.407 mmoles/kg. During the first hour after the-MT injection the declines of DA and NA respectively were almost identical for both-MT doses. When the whole time-course (0–8 hours) after the high dose was considered, biphasic declines were obtained for both DA and NA, suggesting at least two different catecholamine pools. However, due to toxic effects after the high-MT dose, turnover data have to be interpreted with caution.     

Progressive accumulation of ubiquitin and disappearance of α-synuclein epitope in multiple system atrophy-associated glial cytoplasmic inclusions: triple fluorescence study combined with Gallyas-Braak method

-Synuclein (S) and ubiquitin (Ub) are shared constituents of glial cytoplasmic inclusions (GCIs) and Lewy bodies (LBs), both composed of fibrillary structures. Staining profiles of GCIs were investigated with triple immunofluorescence involving immunostaining for S and Ub, both amplified with catalyzed reporter deposition, and a fluorochrome, thiazin red (TR) that has an affinity to fibrillary structures. After observation for the triple-fluorescent images, the sections were subsequently stained with the Gallyas-Braak method. Sections of putamen, cerebellar white matter and motor cortex from patients suffering from multiple system atrophy (MSA) with varying duration of the disease (4–15 years) were quantified for these staining profiles of Gallyas-positive GCIs. Although most of GCIs were positive for Ub and variably positive for S, they were consistently negative for TR. The result was opposite in LBs in Lewy body disease with variable affinity to TR, suggesting that the construction of GCIs is different from that of LBs. These four staining features (S, Ub, TR and Gallyas) alone failed to exhibit apparent correlation with disease duration, lesion site or severity of degeneration as reported previously. The fraction of S-negative and Ub-positive GCIs, however, linearly increased along the disease progression, while that of S-positive and Ub-negative GCIs decreased in contrast. This reciprocal change suggests that S immunoreactivity in GCIs is being replaced by Ub immunoreactivity during the disease progression, which resulted in the ultimate predominance of S-negative and Ub-positive GCIs in the most advanced case. Interestingly, this predominance of S-negative and Ub-positive GCIs was a feature of motor cortex, where degeneration usually remains mild in spite of robust appearance of Gallyas-positive GCIs. Another fraction, S-positive and Ub-positive GCIs were frequent in cerebellar white matter, suggesting that GCI evolution is heterogeneous and dependent also on area examined. Progressive accumulation of Ub with concomitant disappearance of S epitope and their colocalization, partly shared with LBs, may represent a process of GCI formation, possibly linked to an aspect of degeneration in MSA.     

Immunoglobulin heavy chain gene associations in myasthenia gravis: new evidence for disease heterogeneity

Summary Susceptibility to myasthenia gravis (MG) is known to involve genes residing in the major histocompatibility complex class I and II regions (HLA-B8 and DR3). Immunoglobulin heavy chain constant region (IgCH) allotypes have also shown some associations with MG. We have used restriction fragment length polymorphism analysis with probes to the IgCH switch (S) regions and 1 and the downstream marker D14S1 to investigate 189 Caucasoid patients with well-defined MG. A highly significant increase in the frequency of the 2.6 kilobase (kb) S homozygous genotype and the 2.6 kb S allele was found in patients with disease onset after the age of 40 years (late onset) compared with normal controls (P<0.00075 andP<0.025 respectively). No association was found at the S1 or D14S1 loci. In patients with an associated thymoma there was a moderate increase in the frequency of the 2.6 kb S and 7.4 kb S1 genotypes. These results independently support the previous separation of the late-onset subgroup. Finally, the stronger associations at S rather than at the downstream Sl, Gm and D14S1 loci suggest that the genes predisposing to MG are located within the variable region of the Ig heavy chain loci.