Rett syndrome molecular diagnosis and implications in genetic counseling

Rett syndrome is a rare genetic X-linked dominant disorder. This syndrome is the most frequent cause of mental retardation in girls. In the classical form of the disease, the presenting signs and the course of development are characteristic. However clinical diagnosis can be very difficult when the expression is not in the classical form. Mutations in MeCP2 are responsible for 80% of cases. When MeCP2 mutation is found in an index case, genetic counseling is similar to that in other X-linked dominant genetic diseases. However, mutations in this gene can cause a spectrum of atypical forms. On the other hand, other genetic conditions like translocations, sex chromosome numerical anomalies, and mutations in other genes can complicate genetic counseling in this syndrome. We present the first case of molecular diagnosis of Rett syndrome in Iran and discuss the recent developments in its genetic counseling.     

In search of a genetic basis for the Rett syndrome

Summary Rett syndrome is a progressive encephalopathy restricted to the female sex. In the present paper a possible genetic cause for this syndrome is discussed, based on data from the literature as well as our own. Our results are in agreement with others regarding no increase in parental age, or in spontaneous abortions rate among the mothers of affected children and with a normal sex ratio among sibs. We have found no chromosome rearrangement detectable with the methods used and no correlation between fra(X)(p22) and the Rett syndrome. We have observed an alteration in the sequence of replication in one of the two types of late-replicating X-chromosome present in normal women, and suggest that this may signify that genes which are active in the late-replicating X-chromosome are inactivated (or vice-versa) in these patients. This fact could be related to the abnormal phenotype observed in Rett syndrome patients.     

A novel pathogenic mutation in FBN2 associated with congenital contractural arachnodactyly for preimplantation genetic diagnosis

正Congenital contractural arachnodactyly (CCA,OMIM:121050),also known as Beals syndrome,belongs to a group of rare autosomal dominant (AD) diseases of connective tissue (Maslen et al.,1997).People with CCA share many distinguishing features,such as arachnodactyly,camp tod actyly,multiple joint contractures(especially finger,elbow,and knee joints),crumpled ears,scoliosis,pectus deformities,and muscular hypoplasia (Jurko et al.,2013).It exhibits no specific geographic or ethnic predilection (Frederic et al.,2009).     

Splicing mutation of the prostacyclin synthase gene in a family associated with hypertension

Prostacyclin inhibits platelet aggregation, smooth muscle cell proliferation, and vasoconstriction. The prostacyclin synthase (PGIS) gene is a candidate gene for cardiovascular disease. The purpose of this study was to locate possible mutations in the PGIS gene related to hypertension and cerebral infarction. Using the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) method, we discovered a T to C transition at the +2 position of the splicing donor site of intron 9 in patients with essential hypertension (EH). In vitro expression analysis of an allelic minigene consisting of exons 8-10 revealed that the nucleotide transition causes skipping of exon 9. This in turn alters the translational reading frame of exon 10 and introduces a premature stop codon (TGA). A three-dimensional model shows that the splice site mutation produces a truncated protein with a deletion in the heme-binding region. This splice site mutation was found in only one subject in 200 EH patients and 200 healthy controls. Analysis of the patient's family members revealed the mutation in two of the three siblings. The urinary excretion of prostacyclin metabolites in subjects with the mutation was significantly decreased. All subjects displaying the splice site mutation in the PGIS gene were hypertensive. In this study, we report a novel splicing mutation in the PGIS gene, which is associated with hypertension in a family. It is thought that this mechanism may involve in the pathophysiology of their hypertension.     

Fetal alcohol syndrome in association with Rett syndrome

Fetal alcohol syndrome in association with RETT syndrome: We report on a girl with neonatal dystrophy, microcephaly, heart defect, and the characteristic features of alcohol embryopathy. Later, she developed distinctive features of RETT syndrome including loss of early acquired developmental skills and presented typical symptoms of RETT syndrome as reduction of communication skills, reduction of hand function, hyperventilation, and grinding of teeth. Molecular analysis of the MECP2 gene revealed the c.808T>C (R270X) mutation located in the nuclear localisation signal sequence of the gene. Our report highlights the importance of considering the diagnosis of RETT syndrome even in patients who are already suffering from a defined disease.     

Modeling Rett syndrome with stem cells

The discovery that somatic cells can be reprogrammed into induced pluripotent stem cells (iPSCs) raised the exciting possibility of modeling diseases with patient-specific cells. Marchetto et?al. (2010) now use iPSC technology to generate, characterize, and treat an in?vitro model for the autism spectrum disorder Rett syndrome.     

Functional deficit associated with a missense Werner syndrome mutation

Werner syndrome (WS) is a rare autosomal recessive disorder caused by mutations in the WRN gene. WRN helicase, a member of the RecQ helicase family, is involved in various DNA metabolic pathways including DNA replication, recombination, DNA repair and telomere maintenance. In this study, we have characterized the G574R missense mutation, which was recently identified in a WS patient. Our biochemical experiments with purified mutant recombinant WRN protein showed that the G574R mutation inhibits ATP binding, and thereby leads to significant decrease in helicase activity. Exonuclease activity of the mutant protein was not significantly affected, whereas its single strand DNA annealing activity was higher than that of wild type. Deficiency in the helicase activity of the mutant may cause defects in replication and other DNA metabolic processes, which in turn could be responsible for the Werner syndrome phenotype in the patient. In contrast to the usual appearance of WS, the G574R patient has normal stature. Thus the short stature normally associated with WS may not be due to helicase deficiency.     

A monozygotic twin pair with Rett syndrome

Summary A five-year-old, monozygotic, Turkish female twin pair with Rett syndrome is described. The twins are almost completely concordant in all clinical signs. This observation suggests a genetic cause of Rett syndrome.     

雷特综合征与多巴胺系统功能障碍

雷特综合征(Rett syndrome)属于神经发育障碍类疾病,主要由X性染色体上mecp2基因突变所致,患者多数为女孩。临床症状于出生后6~18个月逐渐显现,主要表现为头部发育缓慢,已获得的语言及手部目的性运动技能消退,智力障碍,呼吸功能障碍及自闭倾向等。多巴胺系统的功能包括运动调节、奖赏学习、情感、内分泌调控以及药物成瘾等多个方面。由于多巴胺系统在运动和精神方面与雷特综合征部分临床症状存在表面相关性,早期有学者根据临床特征提出雷特综合征患者可能存在多巴胺系统功能障碍,但两者之间是否具有实质性的内在联系以及mecp2基因是否会通过影响多巴胺系统导致相关临床症状是目前雷特综合征研究的一个热点。本文将针对雷特综合征与多巴胺系统功能障碍的相关研究进展作一综述。     

X chromosome-inactivation patterns in patients with Rett syndrome

Rett syndrome (RS) is a complex and severely disabling neurologic disorder, restricted to females. As non-random X inactivation could indicate that the X chromosome has a role in the etiology of the syndrome, we performed molecular analysis based on the differential methylation of the active and inactive X chromosomes with probe M27β, taking into account the parental origin of the two Xs, in 24 RS girls (including a pair of concordant monozygote twins), 22 mothers, and a control group of 30 normal women. The results showed a significantly (Fisher’s exact test) increased frequency of skewed X inactivation in lymphocytes from 15/23 RS compared with 4/22 mothers (P = 0.0031) and 6/30 controls (P = 0.0021). Our results, together with those from the literature, showed that as a group, RS patients are apparently more prone to skewed X inactivation than their mothers and normal controls, and this suggests that the X chromosome is somehow involved in RS etiology. Received: 13 February 1997 / Accepted: 5 November 1997     

Genetic events associated with an insertion mutation in yeast

The his4-912 mutation shares similar genetic properties with mutations promoted by procaryotic insertion elements. This mutation lacks all three his4 functions. Many different classes of His+ revertants have been obtained from his4-912. The most frequent class of His+ revertants results from a site mutation which confers a cold-sensitive His- phenotype. Other classes of revertants contain translocations (one between chromosomes I and III and the other between chromosomes III and XII), a transposition of the his4 region to chromosome VIII, and an inversion of most of the left arm of chromosome III. Another class contains deletions which extend from his4-912 into the his4 region. In each of these classes of revertants, the his4 region is closely linked to the chromosomal aberration. Many of these revertants contain additional changes in chromosome structure (duplication, deletion and aneuploidy) that are unrelated to the reversion of his4-912 to His4+.     

Rationale for an integrated approach to genetic epidemiology

Conclusion: Genetic knowledge is now in the public domain and its interpretation by the media and the citizens brings the issues into the public forum of discussion for the necessary ethical, legal and socio-cultural evaluation of its application. Science is being perceived by some as dangerous and as requiring international regulation. Others feel that genetic knowledge will be the breakthrough that will permit medical progress and individual autonomy with regards to personal health and lifestyle choices. The mapping of the human genome has already yielded valuable information on an increasing number of diseases and their variants. Prevailing popular and journalistic archetypes ("imaginaires") used in the media are perceived by the producers as slowing down the possible application of genetic knowledge. The answers to these dilemmas are not readily apparent nor are they prescribed by classical philosophy of medicine. Since genetic knowledge eventually resides with the individual who carries the genes of disease and/or susceptibility, a logical approach to integration of this knowledge at a societal level would seem to reside with individual education and decision-making. The politics of the ensuing social debate could transform the current social contract since an individual's interests need to be balanced against those of his or her immediate family in the sharing of information. The ethical foundations of such a contract requires the genetic education of "Everyone" as a matter of urgent priority. Genetic education should not serve ideological power struggles between the medical establishment and the ethical-legal alliance. Instead, it should ensure the transfer of knowledge to physicians, to patients, to users, to planners, to social science and humanities researchers and to politicians, so that they may make "informed" and free decisions....     

Mouse rump-white mutation associated with an inversion of Chromosome 5

The rump-white (Rw) mutation in the mouse was previously mapped as part of a cluster of spotting genes on Chromosome (Chr) 5 that includes the dominant spotting (W) and patch (Ph) loci. Recent studies have shown that the W locus encodes the KIT tyrosine kinase cell surface receptor and that Ph is a deletional mutation encompassing the platelet-derived growth factor receptor alpha subunit (Pdgfra) gene. However, the molecular basis of the Rw mutation remains to be established. We have analyzed an interspecific Mus spretus backcross segregating Rw and several loci proximal and distal to the W/Ph/Rw region to study the basis of this mutation. These studies indicated that loci within the En2 to Kit region of the chromosome do not recombine with one another even though they have been separated in other mapping studies presented here and elsewhere. We conducted a series of fluorescent in situ hybridization (FISH) studies with genomic probes to En2, Msx1, D5Buc1, and Kit to compare the physical order of these loci on the Rw and wild-type chromosomes. The Kit locus mapped to approximately the same region on both chromosomes of the Rw heterozygotes, while the positions of En2, Msx1, and D5Buc1 were reversed on the two chromosomes. Taken together, both the genetic and physical mapping data establish that the Rw mutation is associated with an inversion involving loci in the proximal region of Chromosome 5.     

A point mutation in the tyrosine hydroxylase gene associated with Segawa's syndrome

We have examined the molecular basis of Segawa's syndrome in six families with seven affected children. In one family two siblings with this disease carried a point mutation in exon 11 of the tyrosine hydroxylase gene, resulting in an amino acid exchange of Gln³⁸¹ to Lys³⁸¹. These results suggest that a change in tyrosine hydroxylase causes this form of Segawa's syndrome.     

A genetic model with mutation and selection

Two deterministic models of a multiallele population in which mutation and selection both operate are considered, and formulae for the gene frequencies are obtained. Both models are of a diploid population in which selection is additive and mutation is general; generations are discrete and nonoverlapping. In the first model, the stationary solution of the discrete equations is found. In the second, the discrete time process is approximated by a continuous time one, and the resulting differential equations are solved. The transient case for two alleles is solved explicitly, and the results are graphed. An application is given to sequences of sites.     

重复引物PCR技术在超大片段动态突变疾病基因检测中的应用进展

动态突变疾病是指基因编码区或非编码区发生核苷酸重复序列异常扩增所导致的一类遗传性疾病。发生于非翻译区的动态突变常常伴有超大片段重复序列,应用普通PCR法无法对该片段进行扩增,而传统的Southern blot等技术费时费力,无法应用于临床基因诊断。在此背景下,重复引物PCR技术应运而生。本文将分别阐述重复引物PCR技术在强直性肌营养不良症、Friedreich共济失调、脊髓小脑性共济失调10型及C9orf72基因突变引起的额颞叶痴呆或肌萎缩侧索硬化等疾病基因检测中的应用进展。