Association of genetic polymorphisms in methionine metabolism genes with X-linked adrenoleukodystrophy / 中华医学遗传学杂志

<p><b>OBJECTIVE</b>To investigate the association of the polymorphisms of methionine metabolism genes and the phenotype of X-linked adrenoleukodystrophy (X-ALD) and clinical severity.</p><p><b>METHODS</b>The clinical information of 120 X-ALD patients were analyzed and three genetic variants involved in the methionine metabolism, including cystathionine beta-synthase (CBS) c.844_855ins68, 5-methyltetrahydrofolate-homocysteine-S-methyltransferase (MTR) c.2756A to G, and transcobalamin 2 (TC2) c.776 C to G were analyzed by polymerase chain reaction and sequencing. The association between these polymorphisms and phenotype of X-ALD was studied.</p><p><b>RESULTS</b>The frequency of GG genotype of the TC2 c.776 C/G was higher in patients with central nervous system(CNS) demyelination than in controls (P= 0.012). However, the other two polymorphisms did not show any significant associations with the phenotypes.</p><p><b>CONCLUSION</b>The GG genotype of TC2 c.776 C/G may contribute to X-ALD phenotype.</p>

Analysis of the parental origin of MECP2 mutations in patients with Rett syndrome / 中华医学遗传学杂志

<p><b>OBJECTIVE</b>To identify the parental origin of methyl-CpG-binding protein 2 (MECP2) gene mutations in Chinese patients with Rett syndrome.</p><p><b>METHODS</b>Single nucleotide polymorphisms (SNPs) in intron 3 of the MECP2 gene were analyzed by PCR and sequencing in 115 patients with Rett syndrome. Then sequencing of the SNP region was performed for the fathers of the patients who had at least one SNP, to determine which allele was from the father. Then allele-specific PCR was performed and the products were sequenced to see whether the allele from father or mother harbored the mutation.</p><p><b>RESULTS</b>Seventy-six of the 115 patients had at least one SNP. Three hot SNPs were found in these patients. They were: IVS3+22C >G, IVS3+266C >T and IVS3+683C>T. Among the 76 cases, 73 had a paternal origin of MECP2 mutations, and the other 3 had a maternal origin. There were multiple types of MECP2 mutation of the paternal origin, including 4 frame shift, 2 deletion and 67 point (56C >T, 6C >G, 2A >G, 2G >T and 1A >T) mutations. The mutation types of the 3 patients with maternal origin included 2 frame shift and 1 point (C >T) mutation.</p><p><b>CONCLUSION</b>In Chinese RTT patients, the MECP2 mutations are mostly of paternal origin.</p>

Correlation between MECP2 genotype and phenotype in Chinese patients with Rett syndrome / 中华儿科杂志

<p><b>OBJECTIVE</b>Rett syndrome (RTT) is a neurodevelopmental disorder that represents one of the most common genetic causes of mental retardation in girls. The aim of this study was to investigate the correlation between MECP2 genotype and phenotype and thereby not only to provide assistance for clinical care, but also facilitate clinical genetic counseling.</p><p><b>METHOD</b>Individual phenotype characteristic and clinical severity of 126 children with RTT diagnosed by molecular genetic methods were evaluated by using scales of Kerr et al and Scala et al. Statistical package SPSS 12.0 was used for analyses of data. Since the majority of the data were not normally distributed, non-parametric tests were used. The Kruskal-Wallis test/Wilcoxon Mann-Whitney test was employed to compare total severity phenotype scores. The Fisher exact test was used for comparing rates. Statistical significance was set at P < 0.05.</p><p><b>RESULT</b>There were no significant differences in the average overall scores for RTT patients with mutations in the region of methyl-CpG-binding domain (MBD) compared with those mutations in the transcription repression domain (TRD) and C terminal segment (CTS), also patients with nonsense mutations compared with missense mutations, frameshift mutations and large deletions (P > 0.05). The RTT patients with nonsense mutations located in the region of MBD have more severe phenotype than those with missense mutations in the same region (P = 0.016). Among p.T158M, p.R168X, c.806delG and p.R255X, there were no significant differences in the average overall scores (P > 0.05), but there were significant differences in language skill (P = 0.028) and in language impairment rate at different level (P = 0.019).</p><p><b>CONCLUSION</b>There are relationships between MECP2 genotype and phenotype:the RTT patients with nonsense mutations located in MBD tend to develop more severe phenotype;there are significant differences in language skill and language impairment rate in the groups with p.T158M, p.R168X, c.806del and p.R255X, which had higher frequency in children below five-years of age and the p.R168X present with most severe impairment.</p>

Application of long range polymerase chain reaction and DNA direct sequencing in diagnosis of Rett syndrome / 中华儿科杂志

<p><b>OBJECTIVE</b>Rett syndrome (RTT, MIM 312750) is a progressive neurodevelopmental disorder that affects females almost exclusively, caused by mutations in MECP2 gene on chromosome Xq28, with symptoms such as autism, severe mental deficiency, deceleration of head growth, ataxia, loss of purposeful hand function and characteristic stereotypic hand movements. Over 80% MECP2 mutations located in the exon 3 and exon 4 were confirmed by our work and large-scale studies. RTT is defined based on clinical presentation. It is difficult to diagnose in the early life without definite biochemical abnormality, but genetic test is helpful for this. The aim of this study was to investigate the feasibility and clinical significance of applying long range polymerase chain reaction (PCR) to RTT diagnosis and establish a simple, economic, efficient method of genetic diagnosis.</p><p><b>METHOD</b>Genomic DNA was extracted using standard procedures from the peripheral blood leukocytes of each patient. Long range polymerase chain reaction(PCR)and DNA direct sequencing were employed to analyze the exon 3 and 4 of MECP2 gene simultaneity in 40 patients with RTT. The PCR products were checked by using 1.5% agarose gel.</p><p><b>RESULT</b>In total, 18 different MECP2 mutations were identified in 33 of the 40 diagnosed sporadic female patients with RTT. Missense mutations were 16, followed by 14 nonsense mutations and 3 deletions. The 314 base pairs large deletion was identified. The p. T158M mutation (21%, 7/33) was the most common, followed in order of frequency by p. R255X (12%, 4/33), p. R168X and p. R106W (9%, 3/33) respectively, p. R270X and p. Y141X (6%, 2/33) respectively, p. R133C, p. D156H, p. P157L, p. P225R, p. Q244X, p. Q262X, p. R294X, p. R306C, P322L, c. 1005del G, c.1005-1318del 314 bp and c.1127-1179del 53 bp (3%, 1/33), respectively.</p><p><b>CONCLUSION</b>Long range PCR is a simple, economic, quick, precise method of genetic diagnosis and was able to find 83% MECP2 gene mutations in RTT patients in this study. It is helpful for RTT clinical diagnosis in early stage. On the other hand, it may detect recurrent mutations and large deletions at the same time.</p>