Appearances can be deceptive: an APC 1893del4 mutation with unusual properities. Mutations in brief no. 171. Online

During a systematic search for germ-line APC mutations causative of familial adenomatous polyposis, we discovered what appeared to be an insertion mutation while simply checking exon 14PCR products by agarose gel electrophoresis (AGE). On AGE, exon 14PCR product from the known affected member of this family gave two bands: one of normal length, the other retarded on the gel equivalent to an increase in length of some 20-25 bp. Direct sequencing of DNA purified from the two bands gave identical results, and was consistent with amplification from the same two alleles: one wild-type, and the other having an 1893del4 mutation. This suggested that the normal length band on AGE consisted of DNA homoduplexes (normal:normal and mutant:mutant) and the retarded band consisted of DNA heteroduplexes (normal:mutant and mutant:normal). This hypothesis was tested by subjecting purified material from each of the two bands alone to a single cycle of heat denaturation and annealing, which showed that either band was equally capable of regenerating both bands. Because the anomalous migration of the heteroduplexes is observed in the presence of ethidium bromide, it implies that they have a cruciform of cruciform-like structure. This case illustrates the necessity to be aware of anomalous DNA migration and always sequence all putative mutations.     

First mutation (S340X) in choroideremia gene in a Spanish family. Mutations in brief no. 173. Online

A study of choroideremia gene was performed in Spanish families affected with this disorder. One abnormal pattern was detected in exon eight corresponding to a new mutation not described before. The mutation was identified as a nonsense mutation S340X.     

18 bp insertion/duplication with internal missense mutation in human hepatic lipase gene exon 3. Mutations in brief no. 181. Online

Human hepatic lipase (hHL) plays an important role in hydrolysis of triglycerides from plasma lipoproteins. The enzyme also hydrolyzes HDL2 lipids resulting in smaller HDL particles with a lower cholesterol content and properties similar to HDL3. hHL is localized in liver sinusoids, ovary and adrenal gland. These findings propose an influence on processing of cholesterol. Here we report an insertion mutation in exon 3 of hHL. The 18 bp duplication contains an additional internal point mutation (GenBank-Accession #AF037404). The female mutation carrier suffered from severe adiposity with total cholesterol of 291,6mg/dl, HDL-cholesterol of 55,3mg/dl, LDL-cholesterol of 206,8mg/dl and triglycerides of 80,8mg/dl. Following cloning of a PCR-amplified fragment the mutation was confirmed by cycle sequencing. Sequence analysis revealed an inserted repeat of 18 nucleotides. Furthermore the patient carries an additional missense mutation A-->G at nucleotide 9 of the repeat which results in an amino acid exchange from Ile-->Val at codon 4 of the repeat. These data enable us to report the insertion of HisTyrThrValArgVal which might be responsible for the moderate shift in lipid metabolism of the heterozygous patient.     

A novel splice site mutation of the EXT2 gene in a Finnish hereditary multiple exostoses family. Mutations in brief no. 197. Online

Hereditary multiple exostoses is a dominantly inherited disease characterized by multiple benign osteochondromas. The affected individuals have an increased risk of developing sarcoma. A large Finnish family with hereditary multiple exostosis was analyzed to find the disease-causing mutation. Blood samples were obtained from 35 family members, including 21 affected and 14 unaffected individuals. Using 2-point linkage analysis the EXT phenotype was shown to be linked to the recently cloned EXT2 gene on chromosome 11p11. The coding region of the gene was sequenced and a previously unreported splice site mutation found. This G to T transversion within a 5-prime splice donor site following exon 6 was shown to cause aberrant splicing of RNA. The described change is considered to be a novel disease-causing mutation in the EXT2 gene.     

A novel missense mutation D513G in exon 10 of the cystic fibrosis transmembrane conductance regulator (CFTR) gene identified in a French CBAVD patient. Mutations in brief no. 175. Online

Congenital bilateal absence of the vas deferens (CBAVD) with obstructive azoospermia is a congenital reproductive disorder that affects one in 10000 male individuals. The observation that many men presenting with CBAVD have mutations in their CFTR genes had led to the proposal that CBAVD may be a primary genital form of cystic fibrosis. We report here one novel mutation located in exon 10 of the CFTR gene. This mutation, named D513G (A-->G at position 1670), has been found in one of 83 patients with CBAVD from France, the analysis of exon 10 using a chemical clamp DGGE assay allowed us to identify three CF mutations AEF508 (37/166; 22%), AE1507 (1/166; 0/6%) and D513G (1/166; 0.6%), and two variants M470V and E528E (1716 G>A). The novel D513G mutation has not been found in more than 200 non-CF chromosomes and in a sample of 300 CF chromosomes from French classical CF patients.     

A novel mutation of the down-regulated in adenoma gene in a Japanese case with congential chloride diarrhea. Mutations in brief no. 198. Online

Congenital chloride diarrhea (CLD) is an autosomal recessive disease characterized by excretion of watery stool with a high chloride content. Pathogenesis of CLD is a deficient absorption of chloride in exchange for bicarbonate in the ileum and the colon. In 1996, it was reported that 36 patients with CLD had mutations in the down-regulated in adenoma (DRA) gene; 32 Finnish patients had a three base deletion (951delGGT), 2 Polish patients had a one base mutation (371AtoT) and 2 Polish patients had a one base deletion (344delT). In this study we analyzed the DRA gene in a Japanese boy patient with CLD and in members of his family. The patient was found to have a two base deletion (TT) at nucleotide 1526-1527 within codon 509 which results in a frameshift leading to a permature stopping at codon 517. The patient was homozygous for the deletion, his parents and brother were heterozygous, and his sister was normal. This is the first case of CLD identified to carry a mutation of the DRA gene in Asia.     

Mutational analysis of the cystathionine beta-synthase gene: a splicing mutation, two missense mutations and an insertion in patients with homocystinuria. Mutations in brief no. 120. Online

RT-PCR and direct sequence analyses were used to define mutations in the cystathionine beta-synthase (CBS) gene in two unrelated male patients with vitamin B6 nonresponsive homocystinuria. Both patients were compound heterozygotes for CBS alleles containing point mutations. One patient had a maternally derived G->A transition in the splice-donor site of intron 1, resulting in aberrant splicing of CBS mRNA. The other allele contained a missense mutation resulting in the previously reported E144K mutant CBS protein. The second patient had a maternally derived 4 bp insertion in exon 17, predicted to cause a CBS peptide of altered amino acid sequence. A 494G->A transition was found in exon 4 of the other allele, predicting a C165Y substitution. Expression of recombinant CBS protein, containing the C165Y mutation, had no detectable catalytic activity. Each mutation was confirmed in genomic DNA.     

A novel missense mutation Ile538Val in the fibroblast growth factor receptor 3 in hypochondroplasia. Mutations in brief no. 122. Online

Hypochondroplasia and achondroplasia are skeletal dysplasias, characterized by autosomal dominant inheritance and disproportionate short stature, which occurs mainly due to growth failure of the extremities. Both dysplasias have been mapped to fibroblast growth factor receptor 3 (FGFR3) gene. For hypochondroplasia, two point mutations, both responsible for the Asn540Lys substitution in the region coding the tyrosine kinase domain have been reported. Here we report an A to G transition at position 1651, predicting an Ile538Val substitution in the FGFR3, in hypochondroplasia. The substitution is found in a swedish family with three affected members. The criteria for hypochondroplasia were disproportionate short stature and radiological evidence of shortened long bones and decrease or absence of normal increase in interpedicular distances of the lumbar column. The mutation was detected by direct sequencing and restriction enzyme Tai I digestion. The base change was not found in the FGFR3 genes of unaffected members of the family nor in seventy-five unrelated unaffected individuals, suggesting that it was not a polymorphism. The Ile538Val substitution is a conservative amino acid change (a hydrophobic amino acid incorporated for another hydrophobic amino acid). Nevertheless, it is located in the stretch of nine amino acids, which is highly conserved among all the human fibroblast growth factor receptors. Considering the location of this substitution and the segregation with the phenotype in this family, we propose that it is a causative mutation of hypochondroplasia. It is difficult to establish whether the Ile538Val substitution is rare in hypochondroplasia patients or whether the individuals, who have a moderate degree of short stature, rarely seek medical help for the short stature and consequently are rarely diagnosed as affected by hypochondroplasia.     

Novel missense and frameshift mutations in the activin receptor-like kinase-1 gene in hereditary hemorrhagic telangiectasia. Mutations in brief no. 164. Online

Hereditary hemmorrhagic telangiectasia (HHT) is an autosomal dominant disorder characterized by multisystemic vascular dyplasia and recurrent hemorrhage. One of the causative genes is the activin receptor-like kinase-1 (ALK-1) gene located on chromosome 12q13. ALK-1 is an endothelial cell type I receptor for the TGF-beta superfamily of ligands. As a number of mutations have been identified in the kinase domain of ALK-1, we initiated a mutation analysis specifically targeting the first four coding exons of ALK-1 in order to determine if mutations in the extracellular and transmembrane domains are also present in HHT. Six new mutations have been identified. Three frameshift mutations were identified in exons encoding the extracellular and transmembrane domains. These mutations would grossly truncate the ALK-1 protein and are thus classic null alleles. Three new missense mutations within the exons encoding the extracellular domain, in addition to two previously described missense mutations, are located at or near highly conserved cysteines. These mutations may disrupt intra- or inter-molecular disulfide bridges required for ligand binding. The combined data suggest that both severe and subtle changes in the ALK-1 amino acid sequence can lead to receptor dysfunction and result in the HHT disease phenotype.     

A de novo missense mutation (R1623Q) of the SCN5A gene in a Japanese girl with sporadic long QT sydrome. Mutations in brief no. 140. Online

Two missense mutations and a nine-nucleotide deletion of the cardiac sodium channel (SCN5A) gene have been shown to cause long QT syndrome (LQTS) in several familial cases. We identified a novel missense mutation (R1623Q) of the SCN5A gene in a Japanese girl with sporadic LQTS. We used polymerase chain reaction, single-strand conformation polymorphism analysis and DNA sequence analysis to identify a mutation of the SCN5A gene in the patient. A single nucleotide substitution of guanine to adenine, in codon 1612, changed the coding sense of the SCN5A from arginine to glutamine (R1623Q) in the S4 segment of domain IV which is a highly conserved region of the SCN5A. This mutation was not identified in the unaffected biological parents and brother of the patient, and 100 normal, unrelated individuals. This finding is the first evidence of a de nova mutation in SCN5A associated with LQTS.     

Different ocular abnormalities in individuals of a three-generation family caused by a new nonsense mutation in the PST domain of the PAX6 gene. Mutations in brief no. 189. Online

PAX6 is a candidate gene for familial aniridia. We have carried out a mutational analysis of the PAX6 gene in a three-generation family from Germany, containing 5 individuals affected with ocular abnormalities. In all affected individuals, a heterozygous mutation was detected in the PAX6 gene, exchanging tyrosine 369 by a stop codon. The mutation is located in the 3' moiety of the PST domain, at the C terminus of the PAX6 protein. In the affected family members, the same heterozygous mutation leads to distinct phenotypes of varying severity. Most notably, no aniridia was observed in one of the family members carrying the mutation, although other ocular abnormalities (underdeveloped iris and cataracts) were present. We discuss the possibility that small C terminal truncations of the PAX6 protein might lead to less severe or more divergent phenotypes than trancations at internal positions.     

Identification of three novel mutations in the dystrophin gene detected by the heteroduplex/SSCA screening procedure. Mutations in brief no. 222. Online

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are X-linked neuromuscular disorders associated with alterations in the dystrophin gene. Analysis of 45 DMD/BMD patients has identified 18 patients with no deletion in the dystrophin gene. Heteroduplex analysis (HD), single strand conformation analysis (SSCA), and subsequent sequencing, identified five mutations and nine polymorphisms. Three out of the 5 mutations (780C>G, 2501-1g-->t, 9812 9813ins9800-9812) are first reported here. Furthermore we compare the relative efficiencies of the two alternatives methods (HD and SSCA) for screening sequence alterations.     

A novel mutation in the neonatal region of the fibrillin (FBN)1 gene associated with a classical phenotype of Marfan syndrome (MfS). Mutations in brief no. 163. Online

Marfan Syndrome (MfS) is an autosomal dominant inherited connective tissue disorder with variable phenotypic expression of cardiovascular, skeletal and ocular manifestations. Cardiovascular complications, such as aortic aneurysm and dissection drastically reduce life expectancy of individuals with MfS, whereas preventive surgery substantially improves the prognosis of these patients. A number of mutations in the fibrillin 1 (FBN1) gene associated with MfS have been identified to date, demonstrating considerable molecular heterogeneity. One region, however, located around exon 24, exhibits a striking clustering of mutations, which are associated with a severe, socalled neonatal form of MfS. Here we report the first mutation (G2950A) in exon 24 of the neonatal region of the FBN1 gene, associated with a classic MfS phenotype. The mutation leads to the subsitution of valin by isoleucin (V984I), both uncharged amino acids, which only differ in a single methyl group. This defect was identified in a proband with cardiovascular manifestations of MfS by SSCP analysis of PCR-amplified genomic DNA, direct PCR sequencing and RFLP analysis. The substitution was neither detected in the unaffected 4-year old daughter of the proband, nor in 3 of his healthy family members nor in 108 allels from control individuals, suggesting that this mutation is causative for MfS in the patient. Since no other family member of the proband is affected by MfS, the defect described is sporadic. In summary, we identified a novel defect in exon 24 of the neonatal region of the FBN1 gene in a patient with a classic phenotype of MfS, suggesting that conservative substitutions in this region may lead to a less severe phenotype of the disease. This finding further demonstrates the remarkable phenotypic heterogeneity associated with FBN1 mutations and stresses the significance of modifying genes and individual alterations in protein function for the pheontypic expression of the disease.     

Transthyretin Ile73Val is associated with familial amyloidotic polyneuropathy in a Bangladeshi family. Mutations in brief no. 158. Online

Amyloidosis is characterised by the extraceullular deposition of certain different proteins in a distinctively abnormal fibrillar conformation. All types of amyloid fibril share remarkably similar structural and biophysical properties despite substantial chemical heterogeneity among their respective precursor proteins. Hereditary amyloidosis associated with genetically determined protein variants is rare, but is extremely important as a model for studying the pathogenesis of amyloidosis generally. We report a novel mutation of the transthyretin (TTR) coding for TTR Ile73Val which is associated with familial amylodotic polyneuropathy (FAP) in a Bangladeshi family. The mutation was detected by direct sequencing of the PCR-amplified TTR exons. It creates an additional Accl restriction exzyme site in exon 3, allowing confirmation of its presence by RFLP. Amyloid detected in sural nerve and colonic biopsies was shown to be composed of TTR by immunohistochemistry. The predominant clinical features were progressive autonomic and sensori-motor peripheral neuropathy, beginning at age 50 years. The proband's father and two siblings had similar illnesses. These findings indicate Val73 is an amyloidogenic variant of TTR.     

Noval mutation (Y184C) in exon 4 of the beta-sarcoglycan gene identified in a Portuguese patient. Mutations in brief no. 177. Online

We report a novel beta-sarcoglycan gene mutation identified in a 21-year-old Portuguese male with a progressive myopathy of intermediate severity, who had been misdiagnosed as Becker Muscular Dystrophy (BMD) based on clinical observations and muscle immunocytochemical anaylsis with dystrophin antibodies only. Since no detectable deletions or duplications were found in the dystrophin gene, we screened for mutations in the sarcoglycan genes by PCR-SSCP. The patient's sample showed a band of increased mobility in exon 4 of the beta-sarcoglycan gene which, upon sequencing, was found to represent a homozygous A-->G transversion at nucleotide 551, resulting in a tyrosine to cysteine substitution at position 184 (Y184C). Carrier status was ascertained in both parents and a sister. These aberrant conformers were not detected in 85 unrelated control individuals screened by PCR-SSCP analysis. All seven beta-sarcoglycan mutations reported to date are associated with a severe phenotype and occur in exons 3 and 4, which correspond to the immediate extracellular domain of the protein. This region contains five conserved cysteine residues. In our patient, the presence of an extra cysteine residue could interefere with intra- and/or inter-molecular disulphide bond formation. The intermediate phenotype could perhaps result from the assembly of both normal and abnormal complexes, depending on the formation of the disulphide bonds.     

Variable penetrance of familial pheochromocytoma associated with the von Hipple Lindau gene mutation, S68W. Mutations in brief no. 150. Online

Van Hippel-Lindau disease (VHL) is an autosomal dominantly inherited disorder, characterised by the development of clear cell renal carcinomas, CNS hemangioblastomas, retinal angiomas, pancreatic tumors, pheochromocytomas and hepatic cysts. Recently a number of families with dominant familial pheochromocytoma as the only clinical manifestation have been reported to carry mutations in the HVL gene. We describe a family in which a novel VHL S68W mutation was segregating and carrier individuals manifested with variable penetrance of isolated pheochromocytomas. Investigation of this kindred confirmed that a mutation in the VHL gene could produce isolated pheochromocytomas as the only clinical feature and was variably penetrant.     

Two novel mutations of the arylsulfatase B gene in two Italian patients with severe form of mucopolysaccharidosis. Mutations in brief no. 127. Online

Mucopolysaccharidosis type VI (MPS VI) or Maroteaux-Lamy syndrome, is a autosomal recessive disorder, due to the deficiency of the lysosomal enzyme N-acetylgalactosamine-4-sulfatase (arylsufatase B, ASB: EC 3.1.6.12). Three classical forms of the disease have been differentiated: severe, intermediate, mild. Mutational analysis of the ASB gene resulted in the identification of 30 ASB mutant alleles, each of which was found to be unique among unrelated patients, demonstrating a broad molecular heterogeneity of the disease. In this communication we present two novel mutant alleles in two severely affected subjects. Both alterations, the missense mutation G302R and the nonsense Q456X, were found in homozygosity and were confirmed by amplification refractory mutation system (ARMS) or restriction analysis. The missense G302R mutation concerns an amino acid which may be of special importance to the polypeptide, since 302 position is completely conserved in all the eukaryotic sulfatases aligned so far; the nonsense mutation Q456X leads to the translation of a putative mutant ASB protein lacking the last 78 amino acids with a loss of the 8 kD mature polypeptide, one of the two peptides generated by intralysosomal proteolytic processing of the 64kD precursor.