De Novo Mutations Research Articles

Report on de-novo mutation in the MSH2 gene as a rare event in hereditary nonpolyposis colorectal cancer

Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominant predisposition for early-onset colorectal cancer and associated tumour types caused by mutations in DNA mismatch repair genes, mainly MLH1 and MSH2. The Amsterdam criteria, stressing familial tumour events, as well as the less stringent Bethesda criteria, help to raise suspicion of HNPCC. Mutation screening in a colon cancer patient of young age but negative family history revealed the MSH2 splice site mutation c.2006-2A>G. This mutation was present in all three germ cell layers in the patient, but absent in her biological parents, reporting the second case of de-novo germline mutation in MSH2. Our findings suggest that at least in approximately 1% of mutation-positive cases, a de-novo event might be involved. The identification of a newly evolved rare mutation calls for alertness and encourages the application of the Bethesda guidelines and certain clinical and histopathological features to define candidates for HNPCC gene mutation screening despite a negative family history.

Mutation analysis of haemophilia B in the Irish population: increased prevalence caused by founder effect

Haemophilia B generally arises as a result of unique mutations within the F9 gene and occurs with a prevalence of approximately one case per 30 000 males worldwide. The population prevalence of haemophilia B in Ireland at one per 12 500 males is particularly high. To identify the mutations responsible for haemophilia B and to define the biological basis underlying the increased prevalence in the Irish population, we performed sequence analysis of the F9 gene in 51 apparently unrelated kindred. In 18 kindred with severe or moderate haemophilia B, we identified 14 different mutations; these occurred throughout the F9 gene and included small deletions, missense, non-sense and splice-site mutations and included four novel candidate mutations. In contrast to the variety of different causative mutations with moderate or severe haemophilia B, we found three common mutations accounted for 83% (24/29) of Irish kindred with mild haemophilia B. The mutation n-6 G>A in the promoter region of F9 (which results in the characteristic haemophilia B Leyden phenotype) was found in 10 unrelated kindred. The mutation C>T 30933 in exon 8 (Ala271Val) was identified in a further 10 apparently unrelated kindred. Finally, 10430 G>A mutation (Gly60Ser) was observed in four different kindred. Haplotype analysis was performed on the index cases with the most common mutations and supported the hypothesis that the increased population prevalence of mild haemophilia B in the Irish population arose as a result of founder effect rather than an increased incidence of de-novo F9 mutations.

Novel De Novo Mutation in Sulfonylurea Receptor 1 Presenting as Hyperinsulinism in Infancy Followed by Overt Diabetes in Early Adolescence

OBJECTIVE—Congenital hyperinsulinism, usually associated with severe neonatal hypoglycemia, may progress to diabetes, typically during the 4th decade of life in nonpancreatectomized patients. We aimed to genotype the ATP-sensitive K+ channel in a 10.5-year-old girl presenting with overt diabetes following hyperinsulinism in infancy.RESEARCH DESIGN AND METHODS—A female aged 10.5 years presented with new-onset, antibody-negative diabetes (A1C 10.6%). She was born large for gestational age (5 kg) to a nondiabetic mother and developed frequent hypoglycemic episodes, which persisted until age 3 years and responded initially to intravenous glucose and later to oral sweets. Currently, she is fully pubertal and obese (BMI 30.2 kg/m2), with a partially controlled convulsive disorder (since age 1 year) and poor school performance. Glucose levels were >11.1 mmol/l throughout 72 h of continuous glucose monitoring, with low insulin secretion during intravenous glucose tolerance testing. KCNJ11 and ABCC8 mutation analysis was performed, and the mutation identified was characterized in COSm6 cells.RESULTS—A novel, de novo heterozygous ABCC8 sulfonylurea receptor (SUR)1 mutation (R370S) was identified in the patient's DNA but not in that of either parent. Cotransfection of Kir6.2 and mutant SUR1 demonstrate that the mutated protein is expressed efficiently at the cell surface but fails to respond to MgADP, resulting in minimal channel activity. Interestingly, the heterozygous channel (WT:R370S) responded well to glibenclamide, a finding that lead to the successful initiation of sulfonylurea therapy.CONCLUSIONS—This new ABCC8 mutation is associated with neonatal hyperinsulinism progressing within 10 years to insulinopenic diabetes. Consistent with in vitro findings, the patient responded to sulfonylurea treatment. The mechanism causing the relatively rapid loss in β-cell function is not clear, but it may involve mutation-induced increased β-cell apoptosis related to increased metabolic demand.

Functional pulmonary atresia in a patient with neonatal Marfan syndrome caused by a c.3602G>A mutation in exon 29 of the FBN1 gene

Neonatal Marfan syndrome is a severe form of the syndrome mostly caused by de-novo mutations in the fibrillin-1 gene. We report a newborn with neonatal Marfan syndrome and functional pulmonary atresia who died from congestive heart failure on postnatal day 22 despite treatment. He had a mutation in exon 29 of the fibrillin-1 gene at position c.3602G>A. Functional pulmonary atresia may be a life-threatening cardiovascular manifestation of neonatal Marfan syndrome.

7.007 New approach for haplotyping single gene PGD in couples with de-novo mutations

7.007 New approach for haplotyping single gene PGD in couples with de-novo mutations

Noncompaction of the Ventricular Myocardium Is Associated with a De Novo Mutation in the β-Myosin Heavy Chain Gene

Noncompaction of the ventricular myocardium (NVM) is the morphological hallmark of a rare familial or sporadic unclassified heart disease of heterogeneous origin. NVM results presumably from a congenital developmental error and has been traced back to single point mutations in various genes. The objective of this study was to determine the underlying genetic defect in a large German family suffering from NVM. Twenty four family members were clinically assessed using advanced imaging techniques. For molecular characterization, a genome-wide linkage analysis was undertaken and the disease locus was mapped to chromosome 14ptel-14q12. Subsequently, two genes of the disease interval, MYH6 and MYH7 (encoding the α- and β-myosin heavy chain, respectively) were sequenced, leading to the identification of a previously unknown de novo missense mutation, c.842G>C, in the gene MYH7. The mutation affects a highly conserved amino acid in the myosin subfragment-1 (R281T). In silico simulations suggest that the mutation R281T prevents the formation of a salt bridge between residues R281 and D325, thereby destabilizing the myosin head. The mutation was exclusively present in morphologically affected family members. A few members of the family displayed NVM in combination with other heart defects, such as dislocation of the tricuspid valve (Ebstein's anomaly, EA) and atrial septal defect (ASD). A high degree of clinical variability was observed, ranging from the absence of symptoms in childhood to cardiac death in the third decade of life. The data presented in this report provide first evidence that a mutation in a sarcomeric protein can cause noncompaction of the ventricular myocardium.

Costello syndrome and related disorders

Costello syndrome is a rare congenital disorder affecting multiple organ systems, encompassing severe failure to thrive, cardiac anomalies including hypertrophic cardiomyopathy and atrial tachycardia, tumor predisposition, and cognitive impairment. Costello syndrome shares findings with cardio-facio-cutaneous syndrome and the diagnosis can be challenging. The discovery of gene mutations underlying these and other closely related disorders allows for molecular confirmation of a clinical diagnosis. The identification of germline HRAS mutations in Costello syndrome, and mutations in BRAF, MEK1 and MEK2 in cardio-facio-cutaneous syndrome, uncovered the biologic mechanism for the shared phenotypic findings based on the close interaction of the gene products within the Ras-mitogen-activated protein kinase pathway. Changes in other genes encoding mitogen-activated protein kinase pathway proteins are responsible for Noonan syndrome and the KRAS mutation phenotype. Costello syndrome is caused by heterozygous de-novo point mutations in HRAS, resulting in increased activation of the mitogen-activated protein kinase pathway. Despite their overlapping presentation, Costello syndrome and its related disorders are distinct, and the phenotypes become more distinctive with age. Molecular testing is available and a clinical diagnosis should be reconsidered if it is inconsistent with the molecular result.

T-Cell Autoimmunity May Contribute to Neutropenia in a Patient with Cyclic Neutropenia (CN) and Double De-Novo Mutations in Gfi-1.

CN is a rare autosomal dominant disease characterized by predictable cycling of patients' neutrophils from normal levels to a nadir of ≤100 cells / μL. While heterozygous mutations in the neutrophil elastase gene (ELA2) occur in the majority of patients and altered subcellular trafficking of neutrophil elastase (NE) has also been demonstrated, it remains unknown how these defects lead to the CN phenotype. Similarly, mutations in the gene for the beta subunit of adapter protein 3 (AP3), which binds NE and shuttles it to endosomal vesicles, are present in severely neutropenic patients with Hermansky-Pudlak syndrome (type 2). Interestingly, separate single base-pair mutations in the zinc finger domains of Gfi-1, a gene that maintains the long-term potential of hematopoeitic stem cells and that negatively regulates ELA2 expression, were reported in two different patients with severe congenital neutropenia (SCN). Decreased immunity against recall antigens, and an increase in the proportion of T-cells bearing a mature memory phenotype have also been described in patients with Gfi-1 mutations. As yet, there is no unifying hypothesis linking these various abnormalities. We hypothesized that aberrantly expressed NE, resulting from mutations in ELA2 or associated regulatory genes, could predispose autologous T-cells to target myeloid precursors that aberrantly express NE. Such a reversal of immune tolerance could contribute to neutropenia in CN and SCN patients. We report in a 25 year-old man with CN from birth the simultaneous occurrence of heterozygous mutations in Gfi-1 (N382S and K403R), which were previously identified in separate patients with SCN. Neither mutation was found in this patient's parents however, and sequencing of mRNA encoding PRTN3, ELA2 and AP3 showed no mutations. Because Gfi-1 serves as a transcriptional repressor of ELA2, we hypothesized that NE may be overexpressed and / or mis-trafficked in neutrophils. To address this hypothesis, we analyzed granulocytes by FACS staining and confocal microscopy. NE was disproportionately expressed in the plasma membrane of 75% of the patient's granulocytes compared to only 3% of granulocytes from healthy donors (HD). We have previously demonstrated that cytotoxic T-lymphocytes (CTLs) that recognize proteinase 3 (P3) and NE-derived peptides, such as the HLA-A2 restricted peptide PR1 (VLQELNVTV), can kill leukemia but not normal myeloid cells due to aberrant expression of P3 and NE in the leukemia and that these PR1 specific CTLs (PR1-CTL) are not detected in healthy donors. Because this patient expressed the HLA-A2 allele, we used fluorescently labeled PR1/HLA-A2 tetramers to study whether PR1-CTL were present. Strikingly, 0.5% to 1% of total CD8+ cells from the patient were specific for PR1, as measured over 2 years, whereas no PR1-CTL were present in control HD or the patient's mother, who is also HLA-A2+. The PR1-CTLs co-expressed CCR7 and CD45, consistent with a naïve phenotype, and cytokine secretion after crosslinking the T-cell receptors was similar to controls. These data suggest that aberrant NE expression can lead to a reversal of immune tolerance and a corresponding increase in PR1-CTL. The mechanism of neutrophil cycling in CN patients is not known; however, an autoimmune response against peptides derived from aberrantly expressed granule proteins in myeloid precursors could lead to a CTL-mediated feedback loop that would also be consistent with the chalone hypothesis of feedback regulation already proposed for this disease.

Novel Mutations in Exon 6 of the GFAP Gene Affect a Highly Conserved IF Motif in the Rod Domain 2B and are Associated with Early Onset Infantile Alexander Disease

Alexander disease is a rare disorder of cerebral white matter due to a dysfunction of astrocytes. The most common infantile form presents as a megalencephalic leukodystrophy. Mutations of the GFAP gene, encoding Glial Fibrillary Acidic Protein, have been recognized as the cause of Alexander disease. Glial Fibrillary Acidic Protein is the major intermediate filament protein in astrocytes, its functional rod domain is conserved in sequence and structure among other intermediate filament proteins. We report here two cases of infantile Alexander disease with early onset and severe course, caused by DE NOVO mutations A364 V and Y366C. Both affected GFAP residues are part of a highly conserved coiled-coil trigger motif in the C-terminal end of segment 2B, probably required for the stability of intermediate filament molecules. Comparable effects are seen with mutations of the corresponding residues of the gene coding for keratin 14, another intermediate filament, this further supports the hypothesis that these positions of the trigger motif are generally critical for a normal function of intermediate filaments.

Clinical and Analytical Sensitivities in Hereditary Hemorrhagic Telangiectasia Testing and a Report of de Novo Mutations

Hereditary hemorrhagic telangiectasia is a vascular dysplasia with variable onset and expression. Through identification of a mutation in a proband, mutation testing can be offered to family members. Mutation carriers can receive medical surveillance and treatment before potentially fatal complications arise. In this study, we assessed the significance of clinical evaluations as part of hereditary hemorrhagic telangiectasia diagnostic testing to determine the clinical sensitivity of molecular testing and to report novel mutations. Based on reported clinical symptoms, we classified 142 consecutive cases as affected, suspected, or unlikely affected. We performed temperature gradient capillary electrophoresis and full gene sequencing of both ACVRL1 and ENG genes. We then compared the mutation detection rates between these groups, categorizing sequence variants as mutations, variants of uncertain significance (VUS), or known polymorphisms. Our mutation and VUS detection rate in affected individuals was 74% and 16% in the suspected/unlikely affected group. Sixty-one percent of the mutations and all VUS were novel. The mutation detection rate for temperature gradient capillary electrophoresis was 97%. Our results suggest that a careful clinical evaluation increases the mutation detection rate. We have confirmed the occurrence of de novo mutations in three patients. Our results also show that temperature gradient capillary electrophoresis is an efficient mutation screening method.

Vaccines, Encephalopathies, and Mutations

De-Novo Mutations of the Sodium Channel Gene SCN1A in Alleged Vaccine Encephalopathy: A Retrospective Study. Berkovic SF, Harkin L, McMahon JM, Pelekanos JT, Zuberi SM, Wirrell EC, Gill DS, Iona X, Mulley JC, Scheffer IE. Lancet Neurol 2006;5:488–492. Background Vaccination, particularly for pertussis, has been implicated as a direct cause of an encephalopathy with refractory seizures and intellectual impairment. We postulated that cases of so-called vaccine encephalopathy could have mutations in the neuronal sodium channel α1 subunit gene ( SCN1A) because of a clinical resemblance to severe myoclonic epilepsy of infancy (SMEI) for which such mutations have been identified. Methods We retrospectively studied 14 patients with alleged vaccine encephalopathy in whom the first seizure occurred within 72 h of vaccination. We reviewed the relation to vaccination from source records and assessed the specific epilepsy phenotype. Mutations in SCN1A were identified by PCR amplification and denaturing high performance liquid chromatography analysis, with subsequent sequencing. Parental DNA was examined to ascertain the origin of the mutation. Results SCN1A mutations were identified in 11 of 14 patients with alleged vaccine encephalopathy; a diagnosis of a specific epilepsy syndrome was made in all 14 cases. Five mutations predicted truncation of the protein and six were missense in conserved regions of the molecule. In all nine cases where parental DNA was available the mutations arose de novo. Clinical-molecular correlation showed mutations in eight of eight cases with phenotypes of SMEI, in three of four cases with borderline SMEI, but not in two cases with Lennox–Gastaut syndrome. Conclusion Cases of alleged vaccine encephalopathy could in fact be a genetically determined epileptic encephalopathy that arose de novo. These findings have important clinical implications for diagnosis and management of encephalopathy and, if confirmed in other cohorts, major societal implications for the general acceptance of vaccination.

G.P.4.01 Rare congenital presentation of Emery-Dreifuss muscular dystrophy due to a novel de-novo LMNA mutation R249W

G.P.4.01 Rare congenital presentation of Emery-Dreifuss muscular dystrophy due to a novel de-novo LMNA mutation R249W

22q11.2 deletion syndrome as a natural model for COMT haploinsufficiency-related dopaminergic dysfunction in ADHD

In the current issue of IJNP Gothelf and co-workers report an important study which sheds light on the association between chromosome 22q11.2 deletion syndrome (22q11.2 DS; velocardiofacial syndrome, VCFS), dopaminergic transmission, and psychiatric disorders. 22q11.2 DS occurs in at least 1/5000 live births and thus is the most common chromosomal deletion syndrome in humans (Botto et al., 2003). The deletion in the long arm of chromosome 22, usually comprises up to 3 Mb, and is transmitted dominantly, although most patients suffer from de-novo mutations. The clinical phenotype ranges from immune deficiency with thymal aplasia, congenital heart abnormalities, velopharyngeal insufficiency with hypernasal speech, slight dysmorphy with characteristic facies, to severe syndromal developmental abnormalities with mental retardation (Shprintzen, 2000). Most interestingly for the field of neuropsychiatry, 22q11.2 DS is associated with an increased rate of variety of psychiatric disorders. In childhood and adolescence, 22q11.2 DS is associated with attention deficit hyperactivity disorder (ADHD; Antshel et al., 2005; Niklasson et al., 2002), affecting up to 55% of the patients (Gothelf et al., 2004). Another, less frequent comorbidity in adolescence seems to be obsessive–compulsive disorder (OCD; Gothelf et al., 2006). Finally, there is an increased prevalence for comorbidity with schizophrenic and bipolar affective psychoses in adulthood (Murphy, 2005).

Single-sperm analysis for haplotype construction of de-novo paternal mutations: application to PGD for neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder caused by mutations in the neurofibromin gene. Approximately, 50% of cases are caused by de-novo mutations. Even when the NF1 mutation is known, accuracy of PGD is highly enhanced by simultaneous analysis of linked markers. In a childless couple referred to PGD, the male carried a de-novo mutation, precluding the possibility of typing relatives to establish the mutation-associated haplotype. We developed a single-sperm haplotype analysis strategy to establish the haplotype linked to the NF1 mutation. Spermatozoa from freshly ejaculated semen were used as a substrate for multiplex PCR on single sperm. In addition to the NF1 mutation, six informative polymorphic markers flanking the NF1 gene (D17S1294, D17S1849, D17S841, D17S975, NF1TG2 and NF1AC5) were linked to individual alleles in single sperm from the affected male. Single-sperm analysis established the haplotypes of both mutant and wild-type NF1 alleles and enabled the implementation of a PGD protocol using polymorphic marker analysis. This method is generally applicable to PGD for any disease in which the haplotype of paternal mutations cannot be determined by typing relatives.

De-novo mutations of the sodium channel gene SCN1A in alleged vaccine encephalopathy: a retrospective study

Vaccination, particularly for pertussis, has been implicated as a direct cause of an encephalopathy with refractory seizures and intellectual impairment. We postulated that cases of so-called vaccine encephalopathy could have mutations in the neuronal sodium channel alpha1 subunit gene (SCN1A) because of a clinical resemblance to severe myoclonic epilepsy of infancy (SMEI) for which such mutations have been identified. We retrospectively studied 14 patients with alleged vaccine encephalopathy in whom the first seizure occurred within 72 h of vaccination. We reviewed the relation to vaccination from source records and assessed the specific epilepsy phenotype. Mutations in SCN1A were identified by PCR amplification and denaturing high performance liquid chromatography analysis, with subsequent sequencing. Parental DNA was examined to ascertain the origin of the mutation. SCN1A mutations were identified in 11 of 14 patients with alleged vaccine encephalopathy; a diagnosis of a specific epilepsy syndrome was made in all 14 cases. Five mutations predicted truncation of the protein and six were missense in conserved regions of the molecule. In all nine cases where parental DNA was available the mutations arose de novo. Clinical-molecular correlation showed mutations in eight of eight cases with phenotypes of SMEI, in three of four cases with borderline SMEI, but not in two cases with Lennox-Gastaut syndrome. Cases of alleged vaccine encephalopathy could in fact be a genetically determined epileptic encephalopathy that arose de novo. These findings have important clinical implications for diagnosis and management of encephalopathy and, if confirmed in other cohorts, major societal implications for the general acceptance of vaccination.

Disease severity in dominant Emery Dreifuss is increased by mutations in both emerin and desmin proteins

Individuals with the same genetic disorder often show remarkable differences in clinical severity, a finding generally attributed to the genetic background. We identified two patients with genetically proven Emery-Dreifuss muscular dystrophy (EDMD) who followed an unusual course and had uncommon clinicopathological findings. We hypothesized digenic inheritance and looked for additional molecular explanations. Mutations in additional separate genes were identified in both patients. The first patient was a member of a family with molecularly proven X-linked EDMD. However, the clinical features were unusually severe for this condition in the propositus: he presented at 2.5 years with severe proximal weakness and markedly elevated serum creatine kinase. Muscle weakness rapidly progressed, leading to loss of independent ambulation by the age of 12. In addition, the patient developed cardiac conduction system disease requiring pacing at the age of 11 and severe dilated cardiomyopathy in the early teens. Despite pacing, he had several syncopal episodes attributed to ventricular dysrhythmias. As these resemble the cardiac features of patients with the autosomal dominant variant of EDMD, we examined the lamin A/C gene, identifying a de-novo mutation in the propositus. The second patient had a cardioskeletal myopathy, similar to his mother who had died more than 20 years previously. Because of the dominant family history, a laminopathy was suspected and a mutation in exon 11 of the LMNA gene was identified. This mutation, however, was not present in his mother, but instead, surprisingly, was identified in his virtually asymptomatic father. Unusual accumulations of desmin found in the cardiac muscle of the propositus prompted us to examine the desmin gene in this patient, and in so doing, we identified a desmin mutation, in addition to the LMNA mutation in the propositus. These cases suggest that separate mutations in related proteins that are believed to interact, or that represent different parts of a presumed functional pathway, may synergistically contribute to disease severity in autosomal dominant EDMD. Furthermore, digenic inheritance may well contribute to the clinical severity of many other neuromuscular disorders.

Congenital cataract and macular hypoplasia in humans associated with a de novo mutation in CRYAA and compound heterozygous mutations in P

An isolated form of congenital cataract associated with macular hypoplasia and a generally hypopigmented fundus in infancy was observed in a German family. To test the hypothesis that a de-novo mutation had occurred in one of the parental germ lines, a functional candidate gene approach was applied. The family was carefully examined by a senior paediatric ophthalmologist according to routine procedures (slit lamp, funduscopy, ERG). Blood was taken from the proband and his parents, genomic DNA was isolated and some candidate genes for cataract (CRYAA, CRYBB2, GJA8) or macular hypoplasia (OA1, P) or both (PAX6) were analyzed. The proband showed bilateral cataracts at the age of 4 months; the fundus appeared pale, the optic disc grayish, and macular reflexes were absent. After cataract surgery, the nystagmus persisted, and a control ERG at age 9 years showed essentially normal scotopic and photopic wave forms. An infectious aetiology as well as galactosemia were excluded. However, a heterozygous mutation was found in the proband in exon 1 of CRYAA (62 C-->T), which leads to an exchange from Arg to Leu at amino acid position 21 (R21L). This sequence alteration was not found in the parents and in 96 randomly selected DNA samples from ophthalmologically normal individuals of the KORA S4 study population. In addition, two heterozygous mutations in P were identified (R419Q and A481T); one of both was present in each of the unaffected parents. Based upon the unique finding of the mutation and the expression of CRYAA in the lens, this R21L mutation in the CRYAA is considered to be causative for the dominant cataract phenotype. Moreover, the macular hypoplasia has to be considered a concerted interaction with compound heterozygous mutations in the P gene manifesting a mild form of oculocutaneous albinism. Nevertheless, this combination is rare and future studies will focus on identifying similar phenotypes.

Recurrent De Novo Mutations of SCN1A in Severe Myoclonic Epilepsy of Infancy

Mutations in the voltage-gated sodium channel gene SCN1A are a major cause of severe myoclonic epilepsy of infancy (Dravet syndrome) and generalized epilepsy with febrile seizures plus. This study reports the identification of six de novo SCN1A mutations in patients with severe myoclonic epilepsy of infancy, including a tetranucleotide deletion in exon 26. The same deletion was previously observed in two unrelated patients and appears to result from slipped-strand mispairing of a direct repeat during deoxyribonucleic acid replication. Review of the literature indicates that recurrent mutations account for 25% of SCN1A mutations in severe myoclonic epilepsy of infancy, including six sites of deamination at CpG dinucleotides.

Novel EGR2 mutation R359Q is associated with CMT type 1 and progressive scoliosis

Mutations in the early growth response 2 gene (EGR2) cause demyelinating neuropathies differing in severity and age of onset. We tested 46 unrelated Czech patients with dominant or sporadic demyelinating CMT neuropathy for mutations in the EGR2 gene. One novel de-novo mutation (Arg359Gln, R359Q) was identified in heterozygous state in a patient with a typical CMT1 phenotype, progressive moderate thoracolumbar scoliosis and without clinical signs of cranial nerve dysfunction. This patient is presently less affected compared to previously described Dejerine–Sottas neuropathy (DSN) patients carrying another substitution at codon 359 (Arg359Trp, R359W). This report shows that EGR2 mutations are rare in Czech patients with demyelinating type of CMT and suggests that different substitutions at codon 359 of EGR2 can cause significantly different phenotypes.

Epidermolysis Bullosa Simplex: Recurrent and De Novo Mutations in the KRT5 and KRT14 Genes, Phenotype/Genotype Correlations, and Implications for Genetic Counseling and Prenatal Diagnosis

Epidermolysis bullosa simplex (EBS) is a mechano-bullous disorder characterized by intraepidermal blistering within the basal keratinocytes as a result of trauma to the skin. As part of the DNA diagnostics program, our laboratory has analyzed a cohort of 57 patients with the initial referral diagnosis of EBS. Among these patients, 18 were found to harbor heterozygous mutations in the keratin 5 or keratin 14 genes, KRT5 and KRT14, respectively, whereas in 14 cases, the disease was associated with mutations in both alleles of the plectin gene. Among the keratin mutations, 12 were distinct and six were novel, and in most cases there was no family history of a blistering disease. Prenatal diagnosis of eight pregnancies with keratin gene mutations, at risk for EBS either because one of the parents was affected (three cases) or history of a previously affected child as a result of a de novo mutation (five cases), predicted two fetuses being affected and six being normal. No recurrence of the de novo mutations in these pregnancies was disclosed. Collectively, the data suggest that a significant number of cases diagnosed as EBS are due to plectin mutations, and many cases result from de novo mutations in KRT5 and KRT14 genes. These findings have implications for genetic counseling and prenatal diagnosis for EBS.