Mutational screening of <Emphasis Type="Italic">ARX</Emphasis> gene in Brazilian males with mental retardation of unknown etiology

ARX gene mutations have been known as important causes of developmental and neurological disorders and are responsible for a large spectrum of abnormal phenotypes, includeing syndromic as well as nonsyndromic forms of mental retardation. We have screened the entire coding and flanking intronic sequences of ARX gene in 143 mentally impaired males in order to investigate the contribution of ARX mutations to mental retardation in the population of Rio de Janeiro, Brazil. Three sequence variants were identified: one patient had the most recurrent mutation already observed in ARX gene, the c.428_451dup(24 bp), two patients presented the c.1347C>T (p.G449G) in exon 4, and one patient had the intronic variant c.1074-3T>C. Although two of these alterations were considered polymorphisms, the known pathogenic variant c.428_451dup(24 bp) was found at a high rate (4.8%) among X-linked mental retardation (XLMR) families. Our results, the first in Latin America, reinforce the idea that ARX mutations are relevant to mental retardation and are indicative that molecular screening of exon 2 should be considered in males with mental retardation of unknown etiology, associated or not with neurological manifestations, especially in familial cases.     

A novel frame shift mutation in the PQBP1 gene identified in a Tunisian family with X-linked mental retardation

Mental retardation (MR) is the most frequent cause of serious handicap in children and young adults. Despite recent progress, in most cases the molecular defects underlying this disorder remain unknown. Linkage studies followed by mutational analysis of known X-chromosomal genes related to mental retardation (MRX genes) localized within defined genetic intervals represent a rational strategy to identify a genetic cause of the disorder. Here, we report a Tunisian family including 3 males with severe to mild mental retardation, short stature, lean body and microcephaly; we mapped the disease to a unique interval encompassing Xp21.1-Xq21.33 (with a maximum LOD score of 0.90). Subsequent mutation analysis of genes located in this interval allowed us to identify a truncating mutation in the PQBP1 gene. This mutation is an insertion of an adenosine residue in exon 5 (c.631insA). This frameshift insertion causes premature stop codon at amino acid position 226. The observed mutation was found in all males with MR in this family. Together with previously reported observations, our data further confirm that PQBP1 gene should be tested for males showing mental retardation, short stature, lean body and microcephaly.     

Mutation analysis of the <Emphasis Type="Italic">MECP2</Emphasis> gene in patients of Slavic origin with Rett syndrome: novel mutations and polymorphisms

Rett syndrome (RTT), an X-linked dominant neurodevelopmental disorder in females, is caused mainly by de novo mutations in the methyl-CpG-binding protein 2 gene (MECP2). Here we report mutation analysis of the MECP2 gene in 87 patients with RTT from the Czech and Slovak Republics, and Ukraine. The patients, all girls, with classical RTT were investigated for mutations using bi-directional DNA sequencing and conformation sensitive gel electrophoresis analysis of the coding sequence and exon/intron boundaries of the MECP2 gene. Restriction fragment length polymorphism analysis was performed to confirm the mutations that cause the creation or abolition of the restriction site. Mutation-negative cases were subsequently examined by multiple ligation-dependent probe amplification (MLPA) to identify large deletions. Mutation screening revealed 31 different mutations in 68 patients and 12 non-pathogenic polymorphisms. Six mutations have not been previously published: two point mutations (323T>A, 904C>T), three deletions (189_190delGA, 816_832del17, 1069delAGC) and one deletion/inversion (1063_1236del174;1189_1231inv43). MLPA analysis revealed large deletions in two patients. The detection rate was 78.16%. Our results confirm the high frequency of MECP2 mutations in females with RTT and provide data concerning the mutation heterogeneity in the Slavic population.     

Mutational screening of the RB1 gene in Italian patients with retinoblastoma reveals 11 novel mutations

Retinoblastoma (RB, OMIM#180200) is the most common intraocular tumour in infancy and early childhood. Constituent mutations in the RB1 gene predispose individuals to RB development. We performed a mutational screening of the RB1 gene in Italian patients affected by RB referred to the Medical Genetics of the University of Siena. In 35 unrelated patients, we identified germline RB1 mutations in 6 out of 9 familial cases (66%) and in 7 out of 26 with no family history of RB (27%). Using the single-strand conformational polymorphism (SSCP) technique, 11 novel mutations were detected, including 3 nonsense, 5 frameshift and 4 splice-site mutations. Only two of these mutations (1 splice site and 1 missense) were previously reported. The mutation spectrum reflects the published literature, encompassing predominately nonsense or frameshift and splicing mutations. RB1 germline mutation was detected in 37% of our cases. Gross rearrangements outside the investigated region, altered DNA methylation, or mutations in non-coding regions, may be the cause of disease in the remainder of the patients. Some cases, e.g. a case of incomplete penetrance, or variable expressivity ranging from retinoma to multiple tumours, are discussed in detail. In addition, a case of pre-conception genetic counselling resolved by rescue of banked cordonal blood of the affected deceased child is described.     

Molecular screening of patients with nonsyndromic hearing loss from Nanjing city of China

Hearing loss is the most frequent sensory disorder involving a multitude of factors,and at least 50% of cases are due to genetic etiology.To further characterize the molecular etiology of hearing loss in the Chinese population,we recruited a total of 135 unrelated patients with nonsyndromic sensorineural hearing loss (NSHL) for mutational screening of GJB2,GJB3,GJB6,SLC26A4,SLC26A5 IVS2-2A>G and mitochondrial 12SrRNA,tRNA Ser(UCN) by PCR amplification and direct DNA sequencing.The carrier frequencies of deafness-causing mutations in these patients were 35.55% in GJB2,3.70% in GJB6,15.56% in SLC26A4 and 8.14% in mitochondrial 12SrRNA,respectively.The results indicate the necessity of genetic screening for mutations of these causative genes in Chinese population with nonsyndromic hearing loss.     

Mutation spectrum of the PCCA and PCCB genes in Japanese patients with propionic acidemia

Propionic acidemia (PA) is an inborn error of organic acid metabolism caused by a deficiency of propionyl-CoA carboxylase. This enzyme is composed of two non-identical subunits, alpha and beta, which are encoded by the PCCA and PCCB genes, respectively. An enzyme deficiency can result from mutations in either PCCA or PCCB. To elucidate the mutation spectrum in Japanese patients, we have performed a mutation analysis of 30 patients with PA, which included nine previously reported patients. The study revealed that 15 patients were alpha-subunit deficient and 15 patients were beta-subunit deficient. Seven novel mutations were found (IVS18-6C >G, 1746G >A, C398R, G197E and IVS18+1G >A in the PCCA; A153P and IVS9+1G >T in the PCCB). Among these Japanese patients with alpha-subunit deficiencies, 923-924insT, IVS18-6C >G, and R399Q mutations were frequent and the total allelic frequency of these three mutations combined was 56% (17/30). This is in sharp contrast to the mutation spectrum found in Caucasian patients, where no prevalent mutations have been identified. Among the beta-subunit deficiencies, there were three frequent mutations; R410W, T428I, and A153P, whose allelic frequencies were 30, 26.7, and 13.3%, respectively. In conclusion, a limited number of mutations are predominant in both PCCA and PCCB genes among Japanese patients with propionic acidemia.     

Identification of novel mutations in the RSK2 gene (RPS6KA3) in patients with Coffin-Lowry syndrome

The Coffin-Lowry syndrome (CLS) is a rare X-linked semidominant syndrome characterized by severe psychomotor retardation, facial dysmorphism, digit abnormalities and progressive skeletal deformations. CLS is caused by mutations in a gene located in Xp22.2, RPS6KA3. This gene encodes for a growth factor-regulated serine/threonine protein kinase, RSK2 (ribosomal S6 kinase 2), acting in the Ras-mitogen-activated protein kinase signaling pathway. Mutations in the RPS6KA3 gene are extremely heterogeneous and lead to premature termination of translation and/or to loss of phosphotransferase activity of the RSK2 protein. Screening for RSK2 mutations is essential in most cases to confirm the diagnosis as well as for genetic counseling. Here we present 44 novel mutations in RSK2 causing CLS. The overall number of CLS mutations reported now is 128. Thirty-three percent of mutations are missense mutations, 15% nonsense mutations, 20% splicing errors and 29% short deletion or insertion events. Only four large deletions have so far been found. They are distributed throughout the RPS6KA3 gene, and the majority has been found in a single family. This study further confirms the high rate of new mutations at the RSK2 locus. It is important to consider the possibility of mosaicism when providing genetic counseling in CLS families.     

Mutation screening of the HTR2B gene in patients with Tourette syndrome

Tourette syndrome (TS), a neurological disorder with a reported prevalence frequency ranging from 0.7% to 4.2%, is manifested by motor and phonic tics and associated with a variety of behavioral abnormalities including impulsivity. Clinical, neuroimaging and other studies support dysfunction of the dopamine and 5-hydroxytryptamine neurotransmitter systems in TS. To determine whether TS is associated with mutation in the 5-hydroxytryptamine receptor 2B gene (HTR2B), which has been also implicated in impulsivity, we screened 132 Caucasian and 128 Chinese Han patients with TS. Two novel (c.188T>G, Met63Arg; c.1346G>A, Arg449Gln) and three known (rs61731726, Gly51Gln; rs200541113, Lys324Asn; rs61731723, Asn438Asn) nucleotide variants were found. Further analysis of sex, age, and ethnically matched normal controls (138 Caucasians and 248 Chinese Han individuals), as well as an affected family member, indicated that these variants may not be pathogenically relevant, suggesting that variants in the HTR2B gene may play little or no role in the development of TS.     

Fragile (X) syndrome: a study of the psychological profile in 23 prepubertal patients

In this study a further analysis of the psychological profile in the prepubertal fragile (X) (fra(X] male was performed. The results of the psycho-diagnostic examination of 23 fra(X) boys were compared to a control group of 17 males of the same age with 'non-specific' mental retardation. A number of important quantitative and qualitative differences were observed between the two groups. In the preschool age group the majority of fra(X) boys was mildly mentally retarded. In the school-age group, however, most boys were moderately to severely mentally retarded. This indication of a decline in intellectual performance with age in the fra(X) syndrome was confirmed by a longitudinal individual follow-up of seven fra(X) boys in this age group. In contrast to intellectual performance, appearance of the attention deficit disorder (or hyperkinesis), with its attendent overactivity and impulsiveness, decreases with age, and is independent of the intellectual level. Autistic behaviour was more frequently observed in the youngest fra(X) males, and was more pronounced in the moderately mentally retarded. In more than 50% of the boys of preschool age the association of hyperkinesis and autistic features was found. Language and speech development in the fra(X) syndrome is both symptomatic and specific. Beside a severe, global speech retardation, there are some distinct speech characteristics in the young fra(X) males such as rapid speech rhythm, speech impulsiveness and perseverative speech.     

Mutation analysis of the GNE gene in Korean patients with distal myopathy with rimmed vacuoles

Distal myopathy with rimmed vacuoles (DMRV; MIM 605820) is an autosomal recessive neuromuscular disorder characterized by weakness of the anterior compartment of the lower limbs, sparing the quadriceps muscles. Recently, mutations in the UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase (GNE) gene have been identified as the genetic basis of DMRV. To investigate the mutation spectrum of the GNE gene in Korean patients with DMRV, we performed clinical and genetic analysis of nine unrelated patients suspected to have DMRV. Direct sequencing analysis revealed that eight out of nine patients (88.9%) were either homozygous or compound heterozygous for GNE gene mutations, including three known (C13S, R129Q, and V572L) and two novel mutations (M29T and A591P). The allelic frequencies of the V572L and C13S mutations were 68.8% (11/16) and 12.5% (2/16), respectively. These results suggest that screening for GNE gene mutations in patients suspected to have DMRV would be helpful for molecular diagnosis of DMRV in the Korean population. An erratum to this article can be found at     

Mutation screening of all 65 exons of the fibrillin-1 gene in 60 patients with Marfan syndrome: Report of 12 novel mutations

Mutations in the fibrillin-1 gene on chromosome 15q21.1 have been found to cause Marfan syndrome, a dominantly inherited disorder characterised by clinically variable skeletal, ocular, and cardiovascular abnormalities. In this study we screened all 65 exons of the fibrillin-1 gene in 20 Marfan syndrome families where at least two affected individuals were characterised and available for analysis, another 30 families with only one affected member available for analysis, and in 10 sporadic cases. In large well-characterised families with more than four affected individuals, the detection rate for mutations rose to 78% (7/9), in families with either two or three affected members 27% (3/11). In families where only one affected family member was available, the mutation detection rate was 17% (5/30), and in sporadic cases it was 20% (2/10). In addition, we found eight neutral polymorphisms. Twelve of the 17 disease-causing mutations identified have not been previously described, thus raising the total number of different fibrillin-1 mutations reported to 85 in 94 unrelated cases. Hum Mutat 10:280–289, 1997. © 1997 Wiley-Liss, Inc.     

Gap junction beta 1 (<Emphasis Type="Italic">GJB1</Emphasis>) gene mutations in Italian patients with X-linked Charcot-Marie-Tooth disease

X-linked Charcot-Marie-Tooth disease (CMT1X) is a peripheral neuropathy transmitted in a dominant manner and caused by mutations in the Connexin 32 (Cx32) gene (GJB1, gap junction beta 1). Here we report the mutation analysis of the GJB1 gene in 76 subjects with possible CMT1 and absence of 17p11.2 duplication, and in 38 CMT2 patients without mutations in CMT2-associated-genes, selected from a cohort of 684 patients with peripheral sensory-motor neuropathy. The analysis was performed by direct sequencing of the coding sequence and exon/intron boundaries of the GJB1 gene. The mutation screening identified 22 mutations in GJB1, eight of which have not been previously published: six point mutations (c.50C > G, c.107T > A, c.545C > T, c.545C > G, c.548G > C, c.791G > T) and two deletions (c.84delC, c.573_581delCGTCTTCAT). The GJB1 mutation frequency (19.3%) and the clinical heterogeneity of our patients suggest searching for GJB1 mutations in all CMT cases without the 17p11.2 duplication, regardless of the gender of the proband, as well as in CMT2 patients with possible X-linked inheritance.     

Mediterranean Founder Mutation Database (MFMD): Taking Advantage from Founder Mutations in Genetics Diagnosis,Genetic Diversity and Migration History of the Mediterranean Population

The Mediterranean basin has been the theater of migration crossroads followed by settlement of several societies and cultures in prehistoric and historical times, with important consequences on genetic and genomic determinisms. Here, we present the Mediterranean Founder Mutation Database (MFMD), established to offer web‐based access to founder mutation information in the Mediterranean population. Mutation data were collected from the literature and other online resources and systematically reviewed and assembled into this database. The information provided for each founder mutation includes DNA change, amino‐acid change, mutation type and mutation effect, as well as mutation frequency and coalescence time when available. Currently, the database contains 383 founder mutations found in 210 genes related to 219 diseases. We believe that MFMD will help scientists and physicians to design more rapid and less expensive genetic diagnostic tests. Moreover, the coalescence time of founder mutations gives an overview about the migration history of the Mediterranean population. MFMD can be publicly accessed from http://mfmd.pasteur.ma .     

Mutation screening of the dopamine D2 receptor gene in attention‐deficit hyperactivity disorder subtypes: Preliminary report of a research strategy

Attention‐deficit hyperactivity disorder (ADHD) is a highly heritable syndrome with onset in childhood that is associated with clinical response to drugs, which increase the release of monoamines, especially dopamine. A variety of studies have reported on genetic associations of ADHD with polymorphisms for various component genes of the dopamine pathway. The promise of preliminary associations found with several genes is mitigated by the significant controversy that exists over what are the appropriate clinical characteristics of ADHD associated with its familial transmission. In the current report, we describe a strategy for mutation screening in common, complex disorders and its application to the systematic screening for coding region variation in the dopamine D2 receptor (DRD2) gene. We used groups of individuals who met diagnostic criteria for DSM‐IV–defined ADHD subtypes, as well as recently defined latent class criteria for pure familial forms of ADHD. No coding region sequence variations were identified in the DRD2 gene that met our requirements for prevalence to be considered a candidate variant contributing to susceptibility for ADHD. © 2001 Wiley‐Liss, Inc.     

A mutation in the cathepsin D gene (CTSD) in American Bulldogs with neuronal ceroid lipofuscinosis

We obtained DNA, brains, and eyes from American Bulldogs with neurodegeneration due to neuronal ceroid lipofuscinosis (NCL). The diagnosis of NCL was confirmed by detection of autofluorescent cytoplasmic inclusions within neurons throughout the brains, in retinal ganglion cells, and along outer limiting membranes of the retinas. Electron microscopy revealed that the inclusions had coarsely granular matrices surrounding well-delineated spherical structures and that the inclusions near the retinal outer limiting membranes were within photoreceptor cells, mostly cones. Affected American Bulldogs were homozygous for the A allele of a G to A transition in the cathepsin D gene (CTSD), which predicts the conversion of methionine-199 to an isoleucine. Only the G allele was detected in DNA samples from 131 randomly selected dogs representing 108 breeds other than American Bulldog; however, the A allele had a frequency of 0.28 among 123 genotyped American Bulldogs. Transmission analysis in a 99 dog pedigree of American Bulldogs indicated a probability of less than 10(-7) that alleles from any mutation unlinked to CTSD would be concordant with the pedigree and phenotypes of the dogs. Brain samples from affected dogs had 36% of the cathepsin D-specific enzymatic activity found in control dog brains; whereas, specific enzymatic activities of 15 other lysosomal enzymes were unchanged or increased. Compared to previously described NCLs in mice and sheep that completely lack cathepsin D activity, the clinical course of NCL in the American Bulldogs was less severe and more closely resembled that of many human NCLs.     

Mutation analysis of 218 Chinese patients with Wilson disease revealed no correlation between the canine copper toxicosis gene MURR1 and Wilson disease

Wilson disease (WD) is the most common disorder resulting in hepatic copper overload. A similar form of copper-associated cirrhosis caused by mutations of the canine copper toxicosis MURR1 gene is also observed in Bedlington terriers. Recent studies indicate that MURR1 might influence human copper metabolism and the clinical presentations of WD. However, the correlation between the MURR1 gene and the Chinese patients with WD has not been reported. In the present study, all three exons of the MURR1 gene including the intron–exon boundaries were directly sequenced in 120 unrelated healthy Chinese and 218 unrelated Chinese patients with WD. No mutations were detected in coding and splice site sequence in the human MURR1 gene. A novel polymorphism 3′+119T→A in the 3′ untranslated region (UTR) was identified in three healthy individuals and four patients with two disease-causing mutations in the ATP7B gene and a great diversity of clinical presentations. Of the ATP7B mutations reported here, Gly1268Arg is a novel one. Also, the previously described nucleotide change IVS2+63C→G was detected in 31.66% of normal chromosomes and 26.15% of WD chromosomes. The results have indicated that there is no correlation between MURR1 and WD in the Chinese population.