Plexin B3 is genetically associated with verbal performance and white matter volume in human brain.

The presence of genetic influences on cognitive performance and brain volume is well established. However, specific genetic determinants of the variance of these quantitative traits are not yet known. Plexins act as receptors for semaphorins and are implicated in axon guidance, which is a key process in brain development. We have previously shown that plexin B3 is a highly potent stimulator of neurite outgrowth, which makes its gene PLXNB3 an intriguing candidate gene for traits related to human brain development and cerebral connectivity. We identified several polymorphisms in PLXNB3 predicting changes of amino acids (V598I, E1156D and V1596E) conserved at the corresponding positions of the orthologs in mouse and chimpanzee. PLXNB3 was genotyped in 303 healthy volunteers and 42 male patients with schizophrenia. Cognitive performance was measured with the vocabulary test (Wortschatztest (WST)), a method to estimate roughly general intelligence (g). Brain morphology was characterized by magnetic resonance imaging. Compared to subjects not carrying the modern, human-specific haplotype A, carriers of A scored higher in vocabulary test (WST) irrespective of diagnosis (P=0.0004). This effect could be observed in three independent groups (healthy males: P=0.048; schizophrenic males: P=0.034 and healthy females: P=0.037). Additionally, the haplotype A was associated with increased volume of brain white matter that in turn correlated with performance in the vocabulary test. These findings suggest that plexin B3 may influence cognitive performance, and the development of white matter in vivo in a way similar to its known stimulating effect on neurite outgrowth in vitro. These novel observations warrant further replication in independent samples.

[New diagnostic possibilities in Alport's syndrome]. / Nové moznosti v diagnostice Alportova syndromu.

An overview of immunohistological and molecular genetic methods for diagnosis of Alport syndrome (AS) is given with practical experience from groups of authors' observations. Immunofluorescent investigation using antibodies against alfa chains of collagen IV was performed on cryostat sections from 29 punction nephrobiopsies and 9 skin excisions taken for support of differential diagnosis of AS particularly against the thin membranes glomerulopathy. Alfa chains deviations in other renal diseases were followed in another 14 cases. Molecular genetical investigation of AS by an indirect DNA diagnostics was performed in 35 families with presumed AS and in 27 patients with probable mutation a mutation screening of COL4AS gene by a direct method SSCP was made. The mutation was proved in 10 cases. Because of genotypical and phenotypical variability of AS the diagnostic gain only increases when all the accessible methods are combined.

[DNA diagnosis of the fragile X chromosome syndrome--FRAXA using PCR]. / DNA diagnostika syndromu fragilního X chromozomu--FRAXA pomocí PCR.

BACKGROUND: Fragile X syndrome is gonosomal recessive mental retardation with the frequency 1:1000 in male population. Fragile X syndrome is caused by amplification of CGG repeat in 1. exon of FMT-1 gene. The aim of this study was to set up and validate a rapid and efficient PCR diagnosis to select FRAXA negative patients in population of mental retarded patients. METHODS AND RESULTS: In the set up phase of the method, 196 patients were diagnosed. We were using modified radioactive PCR of CGG. Obtained PCR fragments were separated on 6% denaturing PAGE. Results were correlated with Southern blot analysis using pE5.1 probe. STR-PCR was verified on a large set of patients and shows validity and efficiency of results in the case of pre- and full mutations in male hemizygous patients too. For estimation of carriers with pre- and full mutation by females modified diagnostic approach was developed. There was no difference found between results from PCR and Southern blot analysis. CONCLUSIONS: The PCR method is convenient not only for selection of FRAXA negative patients, but for diagnosis of full mutation and premutation of affected probands.

[Use of CA repeat polymorphism in direct and indirect diagnosis of Duchenne and Becker muscular dystrophy]. / Vyuzitie polymorfizmov CA opakovaní v priamej a nepriamej diagnostike Duchenneovej a Beckerovej muskulárnej dystrofie.

BACKGROUND: DNA analysis makes it possible to confirm the clinical diagnosis of the majority of cases DMD/BMD and to detect at the same time carries and the prenatal diagnosis for relatives at risk. The objective of the present work was to improve the haplotype analysis and to identify the most frequent deletions in carries. METHODS AND RESULTS: The method is based on the initial amplification of several DNA polymorphisms of CA repetitions and subsequent identification of alleles in the denaturation sequencing polyacrylamide gel using radioactive detection system. The system of CA polymorphisms provides information in the great majority of families, it detects the recombination in the DMD gene, which reduces to a minimum the risk of a diagnostic error and provides valuable information on the carriership of deletion. CONCLUSIONS: The introduction of haplotype analysis of CA repetitions is beyond doubt an asset to the prenatal diagnosis of DMD/BMD and assessment of carriership of this serious hereditary disease. The variability of the length of alleles of these markers improves analysis, prenatal diagnosis and makes it possible to rule out or identify deletion in cca 40% carriers.