Overexpression of GDP dissociation inhibitor 1 gene associates with the invasiveness and poor outcomes of colorectal cancer

GDP dissociation inhibitor (GDI) regulates the GDP/GTP exchange reaction of most Rab proteins by inhibiting GDP dissociation. This study evaluated the potential prognostic and predictive value of GDI1 in colorectal cancer (CRC). To address the prognostic power of GDI1, we performed individual and pooled survival analyses on six independent CRC microarray gene expression datasets. GDI1-enriched signatures were also analyzed. Kaplan-Meier and Cox proportional analyses were employed for survival analysis. An immunohistochemistry (IHC) analysis was performed to validate the clinical relevance and prognostic significance of the GDI1 protein level in CRC tissue samples. The results revealed that GDI1 mRNA level was significantly linked with the aggressiveness of CRC, which is compatible with gene set enrichment analysis. A meta-analysis and pooled analysis demonstrated that a higher mRNA GDI1 expression was dramatically correlated with a worse survival in a dose-dependent manner in CRC patients. Further IHC analysis validated that the protein expression of GDI1 in both cytoplasm and membrane also significantly impacted the outcome of CRC patients. In CRC patients with stage III, chemotherapy significantly reduced the relative risk of death in low-GDI1 subgroup (hazard ratio (HR) = 0.22; 95% confidence interval (95% CI) 0.09-0.56, p = 0.0003), but not in high-GDI1 subgroup (HR = 0.63; 95% CI 0.35-1.14, p = 0.1137). Therefore, both high mRNA and protein levels of GDI1 were significantly related to poor outcomes in CRC patients. GD11 may serve as a prognostic biomarker for CRC.

Male infertility and the involvement of the X chromosome

BACKGROUND

Male infertility is a worldwide problem, keeping many researchers puzzled. Besides environmental factors, much attention is paid to single gene defects. In this view, the sex chromosomes are particularly interesting since men only have a single copy of these chromosomes. The involvement of the Y chromosome in male infertility is obvious since the detection of Yq microdeletions. The role of the X chromosome, however, remains less understood.

METHODS

Articles were obtained by searching PubMed until December 2008. A first search attempted to identify genes located on the X chromosome potentially important for spermatogenesis. A second part of the study was focused on those genes for which the role has already been studied in infertile patients.

RESULTS

Multiple genes located on the X chromosome are expressed in testicular tissues. The function of many genes, especially the cancer-testis genes, has not been studied so far. There were striking differences between mouse and human genes. In the second part of the study, the results of mutation analyses of seven genes (AR, SOX3, USP26, NXF2, TAF7L, FATE and AKAP4) are described. Except for AR, no infertility causing mutations have, thus far, been described. It cannot be excluded that some of the observed changes should be considered as risk factors for impaired spermatogenesis.

CONCLUSIONS

It can be concluded that, so far, the mutation analysis of X-linked genes in humans, presumed to be crucial for spermatogenesis or sperm quality, has been disappointing. Other approaches to learn more about male infertility are necessary.

Birth and adaptive evolution of a hominoid gene that supports high neurotransmitter flux

The enzyme glutamate dehydrogenase (GDH) is important for recycling the chief excitatory neurotransmitter, glutamate, during neurotransmission. Human GDH exists in housekeeping and brain-specific isotypes encoded by the genes GLUD1 and GLUD2, respectively. Here we show that GLUD2 originated by retroposition from GLUD1 in the hominoid ancestor less than 23 million years ago. The amino acid changes responsible for the unique brain-specific properties of the enzyme derived from GLUD2 occurred during a period of positive selection after the duplication event.

Mutations in the gene encoding methyl-CpG-binding protein 2 cause Rett syndrome

Rett syndrome is an X-linked dominant neurodevelopmental disorder primarily affecting girls. About 80% of classic Rett syndrome is caused by mutations in the gene for methyl-CpG-binding protein (MeCP2) in Xq28. MeCP2 links DNA methylation to transcriptional repression, and MECP2 mutations likely cause partial or complete loss of function of the protein, leading to inappropriate transcription of downstream genes at critical times in brain development. More severe and milder variant forms can all be caused by similar mutations. Most classic Rett syndrome patients have random X-chromosome inactivation (XCI), but skewed patterns are present in a few. All asymptomatic or mildly mentally delayed female carriers studied to date have non-random XCI patterns, suggesting that this attenuates the deleterious effects of the MECP2 mutations in these women. The finding of non-random XCI patterns in some patients with very early truncations is consistent with this observation and supports that many mutations could cause partial and not complete loss of function. Our observation that the mutant mRNA is stable in three patients with truncating mutations supports this possibility. Further studies will have to be performed to better understand the functional consequences of MECP2 mutations in RTT.

Rett syndrome: methyl-CpG-binding protein 2 mutations and phenotype-genotype correlations

Rett syndrome (RTT) is an X-linked dominant neurodevelopmental disorder that manifests in females, typically after the first year of life. It is a leading cause of mental retardation and autistic behavior in girls and women; a hallmark of the disease is incessant hand movements in the form of wringing, twisting, or clapping. It was recently discovered that RTT is caused by mutations in the methyl-CpG-binding protein 2 (MECP2) gene. MECP2 assists in the transcriptional silencing process via DNA methylation; we hypothesize that disruption of this gene alters the normal developmental expression of various other genes, some of which must account for the peculiar neurologic phenotype of RTT. Molecular studies have identified MECP2 mutations in up to 80% of classic RTT patients; mutation type has some effect on the phenotypic manifestation of RTT, but the pattern of X inactivation seems to determine phenotypic severity. Favorable (skewed) X inactivation can so spare a patient from the effects of mutant MECP2 that they display only the mildest learning disability or no phenotype at all. The unmitigated impact of mutant MECP2 can be inferred from the few males who have been born into RTT kindreds with such severe neonatal encephalopathy that they did not survive their second year. MECP2 mutations thus manifest in a far broader array of phenotypes than classic RTT. This discovery should prove helpful in diagnosing cases of mild learning disability or severe neonatal encephalopathies of unknown cause and also should provide insight into the pathogenesis of RTT.

Molecular genetics of Rett syndrome

Rett syndrome is a neurodevelopmental disorder affecting almost exclusively females. It affects approximately one in 15000 females and is characterized by a loss of purposeful hand use, autism, ataxia and seizure. The disorder is usually sporadic, but rare familial cases have also been reported. Recently it has been shown that familial cases are an X-linked dominant disorder and the disease locus maps to Xq28. A candidate gene called methyl-CpG-binding protein 2 was identified from the Xq28 region and was shown to contain mutations in about 77% of Rett syndrome patients. Since the encoded protein was previously shown to be a global transcriptional repressor, undesired expression of yet unidentified genes that are normally repressed is considered to be pathogenic in Rett syndrome.

A Rett syndrome patient with a ring X chromosome: further evidence for skewing of X inactivation and heterogeneity in the aetiology of the disease

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder, characterised by regression of development in young females. Recently, mutations in the MECP2 gene were found to be present in 80% of sporadic cases, but in much lower frequency (< 30%) among familial cases. Several reports claim that the pattern of X chromosome inactivation (XCI) relates to the penetrance of RTT; in some cases skewed XCI is seen in Rett patients, and in others it is observed among normal carriers. We present here a case of RTT with a 46,X,r(X) in which complete skewed inactivation of the ring was demonstrated. Further, no mutations were found in the MECP2 gene present on the intact X. Our data, in conjunction with two previously published cases of X chromosome abnormalities in RTT, indicate that X chromosome rearrangements are sporadically associated with RTT in conjunction with extreme skewing of X inactivation. Based on our case and reported data, we discuss the evidence for a second X-linked locus for RTT associated with lower penetrance, and a different pattern of XCI, than for MECP2. This would result in a larger proportion of phenotypically normal carrier women transmitting the mutation for this putative second locus, and account for the minority of sporadic and majority of familial cases that are negative for MECP2 mutations.

Genetics of Rett syndrome: properties of the newly discovered gene and pathobiology of the disorder

The recent identification of mutations in the gene methyl-Cpg-binding protein-2 (MECP2) in girls with Rett syndrome (RS) has firmly established the molecular genetic basis of this unique, X-linked, dominant disorder and provides a dramatic conclusion to an intensive, decade-long search. This finding has ramifications far beyond establishing the gene for RS. Recent data indicate that the clinical phenotypes for MECP2 mutations range from mild disability in the mother of a girl with RS to rapidly progressive encephalopathy in her brother. Further, the pathobiology of MECP2 could be a prototype for other disorders of neurodevelopment. MECP2 encodes a methyl-CpG-binding protein (MeCP2), which is critical for transcriptional silencing of an as yet unknown number and type of genes responsible for the pathobiology of RS. As such, this discovery opens up completely new vistas as to fundamental neurobiologic processes, to disease mechanisms in the neurodevelopmental disabilities, and to potential new therapeutic strategies for RS and related disorders.

Rett syndrome and beyond: recurrent spontaneous and familial MECP2 mutations at CpG hotspots

Rett syndrome (RTT) is a neurodevelopmental disorder characterized by loss of acquired skills after a period of normal development in infant girls. The responsible gene, encoding methyl-CpG binding protein 2 (MeCP2), was recently discovered. Here we explore the spectrum of phenotypes resulting from MECP2 mutations. Both nonsense (R168X and R255X) and missense (R106W and R306C) mutations have been found, with multiple recurrences. R168X mutations were identified in six unrelated sporadic cases, as well as in two affected sisters and their normal mother. The missense mutations were de novo and affect conserved domains of MeCP2. All of the nucleotide substitutions involve C-->T transitions at CpG hotspots. A single nucleotide deletion, at codon 137, that creates a L138X stop codon within the methyl-binding domain was found in an individual with features of RTT and incontinentia pigmenti. An 806delG deletion causing a V288X stop in the transcription-repression domain was identified in a woman with motor-coordination problems, mild learning disability, and skewed X inactivation; in her sister and daughter, who were affected with classic RTT; and in her hemizygous son, who died from congenital encephalopathy. Thus, some males with RTT-causing MECP2 mutations may survive to birth, and female heterozygotes with favorably skewed X-inactivation patterns may have little or no involvement. Therefore, MECP2 mutations are not limited to RTT and may be implicated in a much broader phenotypic spectrum.

Molecular approaches to the Rett syndrome gene

Rett syndrome is a neurodevelopmental disorder affecting 1 in 10,000 to 15,000 females worldwide. Apparently normal at birth, girls with Rett syndrome undergo developmental regression and acquire a neurologic and behavioral profile that has been used to define diagnostic criteria for the disorder. Neurochemical and anatomic alterations indicate that Rett syndrome appears to result from an arrest of normal neuronal maturation. Although Rett syndrome generally occurs sporadically, rare familial recurrences indicate a genetic basis for the disorder. Data from familial recurrences are consistent with an X-linked dominant locus causing the classic phenotype in female patients and a distinct, more severe phenotype in hemizygous male patients. Exclusion mapping data from rare kindreds with recurrent Rett syndrome localize the gene to the distal long arm of the X chromosome (Xq27.3-Xqter).

Rett syndrome is caused by mutations in X-linked MECP2, encoding methyl-CpG-binding protein 2

Rett syndrome (RTT, MIM 312750) is a progressive neurodevelopmental disorder and one of the most common causes of mental retardation in females, with an incidence of 1 in 10,000-15,000 (ref. 2). Patients with classic RTT appear to develop normally until 6-18 months of age, then gradually lose speech and purposeful hand use, and develop microcephaly, seizures, autism, ataxia, intermittent hyperventilation and stereotypic hand movements. After initial regression, the condition stabilizes and patients usually survive into adulthood. As RTT occurs almost exclusively in females, it has been proposed that RTT is caused by an X-linked dominant mutation with lethality in hemizygous males. Previous exclusion mapping studies using RTT families mapped the locus to Xq28 (refs 6,9,10,11). Using a systematic gene screening approach, we have identified mutations in the gene (MECP2 ) encoding X-linked methyl-CpG-binding protein 2 (MeCP2) as the cause of some cases of RTT. MeCP2 selectively binds CpG dinucleotides in the mammalian genome and mediates transcriptional repression through interaction with histone deacetylase and the corepressor SIN3A (refs 12,13). In 5 of 21 sporadic patients, we found 3 de novo missense mutations in the region encoding the highly conserved methyl-binding domain (MBD) as well as a de novo frameshift and a de novo nonsense mutation, both of which disrupt the transcription repression domain (TRD). In two affected half-sisters of a RTT family, we found segregation of an additional missense mutation not detected in their obligate carrier mother. This suggests that the mother is a germline mosaic for this mutation. Our study reports the first disease-causing mutations in RTT and points to abnormal epigenetic regulation as the mechanism underlying the pathogenesis of RTT.

Metacarpophalangeal pattern profile and bone age in Rett syndrome: further radiological clues to the diagnosis

Hand radiographs of 100 girls representing 73% of the known Australian population of girls with Rett syndrome, age 20 years or less, were available for this study. Control radiographs were matched for age, sex, and laterality. Bone age was assessed against standard radiographs in Greulich and Pyle [1959: Radiographic Atlas of Skeletal Development of the Hands and Wrist, 2nd ed.]. A metacarpophalangeal pattern (MCPP) profile comparing the relative lengths of the hand bones with mean population norms by age was produced by converting the length of each of the 19 metacarpal and phalangeal bones into a Z score. In girls less than 15 years old, bone age was more advanced in Rett syndrome than in age-matched control girls (left hand P = 0.03, right hand 0.004), but was most advanced in the younger group and normalized with age. In Rett syndrome, the mean Z score for the 19 metacarpal and phalangeal bones was 1.0 in children under 5 years, -0.27 in those aged 5-11 years, and -1.7 in those aged 12 years and over. This variation between age groups was much greater than in the controls. The dips in the MCPP profile occurred at MC2 and D1, and the peaks at M5, P5, and M4. An MCPP profile may provide an additional aid to diagnosis in cases of Rett syndrome where all the criteria are not met, but in children under age 5 years, advanced bone age may be more helpful as a marker.

Familial aggregation in Rett syndrome: what is the evidence for clustering of other disorders in families of affected girls?

Rett syndrome is a neurodevelopmental disorder of unknown cause which affects girls almost exclusively. Apparently normal development in the first year of life is usually followed by loss of skills and the development of stereotypic hand movements. This study has used genetic epidemiological methods including a case control design to examine the evidence for aggregation of other disorders in families of girls with Rett syndrome. In one family there were two sisters with a condition consistent with Rett syndrome. Intellectual disability was not reported more commonly in case families (P = 0.46). However, "learning problems" were slightly commoner (P = 0.05) especially in the parental generation (P = 0.02) and these findings warrant further investigation. Mental illness and seizures were not reported at an increased prevalence. However, we would recommend the use of other strategies to collect information about psychiatric illness. Spinal curvature was reported more commonly in case families (P = 0.07) but no mechanism for clinical verification of this was included in the study. There was an apparent increase in bowel problems in the parents (P = 0.04). The major weaknesses of our study were our inability to validate any diagnosis clinically and the lack of power (due to the comparative rarity of the outcomes). The strengths are that we have been able to collect pedigree data on the families of a substantial proportion of a total population of girls with Rett syndrome and to collect comparative data from a control population. Our reported findings warrant further investigation in a larger study.