Jenni Jonasson

Mitochondrial haplogroup is associated with the phenotype of familial amyloidosis with polyneuropathy in Swedish and French patients.

Familial amyloidotic polyneuropathy (FAP) is a monogenic disease caused by mutations in the transthyretin (TTR) gene. The phenotype of the most common TTR mutation, V30M, varies within and between populations. Oxidative stress and protein misfolding are cellular processes involved in the development of FAP. Because the mitochondria are important for both these processes, we investigated if mitochondrial haplogroups are related to age at onset of the disease in Swedish and French FAP patients. Mitochondrial haplogroup analysis was performed on 25 early‐onset (below 40 years) and 29 late‐onset (above 51 years) Swedish FAP patients. DNA from 249 Swedish individuals served as controls. In addition, 6 early‐onset and 17 late‐onset French FAP patients were examined with 25 French controls. The haplogroup distribution among late‐onset Swedish and French cases was similar to that found in the general populations, whereas among early‐onset cases a different haplogroup distribution was seen. The relatively rare haplogroup K was significantly more common among early‐onset cases. Our findings substantiate the suggestion that a genetic component, still to be found, affecting mitochondrial function has an impact on the amyloid generating process in transthyretin amyloidosis.

Expression of ataxin-7 in CNS and non-CNS tissue of normal and SCA7 individuals

Abstract. Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disorder primarily affecting the cerebellum, brain stem and retina. The disease is caused by an expanded polyglutamine tract in the protein ataxin-7. In this study we analyzed the expression pattern of ataxin-7 in CNS and non-CNS tissue from three SCA7 patients and age-matched controls. SCA7 is a rare autosomal dominant disorder, limiting the number of patients available for analysis. We therefore compiled data on ataxin-7 expression from all SCA7 patients (n=5) and controls (n=7) published to date, and compared with the results obtained in this study. Expression of ataxin-7 was found in neurons throughout the CNS and was highly abundant in Purkinje cells of the cerebellum, in regions of the hippocampus and in cerebral cortex. Ataxin-7 expression was not restricted to regions of pathology, and there were no apparent regional differences in ataxin-7 expression patterns between patients and controls. The subcellular distribution of ataxin-7 was primarily nuclear in all brain regions studied. In cerebellar Purkinje cells, however, differences in subcellular distribution of ataxin-7 were observed between patients and controls of different ages. Here we provide an increased understanding of the distribution of ataxin-7, and the possible implication of subcellular localization of this protein on disease pathology is discussed.

Cloning and expression analysis of the murine homolog of the spinocerebellar ataxia type 7 (SCA7) gene.

Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disease caused by the expansion of a polyglutamine tract in the protein ataxin-7, a protein of unknown function. In order to analyze the expression pattern of wild type ataxin-7 in detail, the murine SCA7 gene homolog was cloned and the expression pattern in mice analyzed. The SCA7 mouse and human gene exhibit a high degree of identity at both DNA (88.2%) and protein (88.7%) level. The CAG repeat region, known to be polymorphic in man, is conserved in mouse but contained only five repeats in all mouse strains analyzed. The arrestin homology domain and the nuclear localization signal found in human ataxin-7 is also conserved in the murine homolog. Expression of ataxin-7 was detected during mouse embryonic development and in all adult mouse tissues examined by northern and western blots. In brain, immunohistological staining revealed an ataxin-7 expression pattern similar to that in human, with ataxin-7 expression in cerebellum, several brainstem nuclei, cerebral cortex and hippocampus. Our data show high conservation of ataxin-7 both structurally and at the level of expression, suggesting a conserved role for the protein in mice and humans.

Founder mutations characterise the mutation panorama in 200 Swedish index cases referred for Long QT syndrome genetic testing

BackgroundLong QT syndrome (LQTS) is an inherited arrhythmic disorder characterised by prolongation of the QT interval on ECG, presence of syncope and sudden death. The symptoms in LQTS patients are highly variable, and genotype influences the clinical course. This study aims to report the spectrum of LQTS mutations in a Swedish cohort.MethodsBetween March 2006 and October 2009, two hundred, unrelated index cases were referred to the Department of Clinical Genetics, Umeå University Hospital, Sweden, for LQTS genetic testing. We scanned five of the LQTS-susceptibility genes (KCNQ1, KCNH2, SCN5A, KCNE1, and KCNE2) for mutations by DHPLC and/or sequencing. We applied MLPA to detect large deletions or duplications in the KCNQ1, KCNH2, SCN5A, KCNE1, and KCNE2 genes. Furthermore, the gene RYR2 was screened in 36 selected LQTS genotype-negative patients to detect cases with the clinically overlapping disease catecholaminergic polymorphic ventricular tachycardia (CPVT).ResultsIn total, a disease-causing mutation was identified in 103 of the 200 (52%) index cases. Of these, altered exon copy numbers in the KCNH2 gene accounted for 2% of the mutations, whereas a RYR2 mutation accounted for 3% of the mutations. The genotype-positive cases stemmed from 64 distinct mutations, of which 28% were novel to this cohort. The majority of the distinct mutations were found in a single case (80%), whereas 20% of the mutations were observed more than once. Two founder mutations, KCNQ1 p.Y111C and KCNQ1 p.R518*, accounted for 25% of the genotype-positive index cases. Genetic cascade screening of 481 relatives to the 103 index cases with an identified mutation revealed 41% mutation carriers who were at risk of cardiac events such as syncope or sudden unexpected death.ConclusionIn this cohort of Swedish index cases with suspected LQTS, a disease-causing mutation was identified in 52% of the referred patients. Copy number variations explained 2% of the mutations and 3 of 36 selected cases (8%) harboured a mutation in the RYR2 gene. The mutation panorama is characterised by founder mutations (25%), even so, this cohort increases the amount of known LQTS-associated mutations, as approximately one-third (28%) of the detected mutations were unique.

Report of five rare or previously unknown amyloidogenic transthyretin mutations disclosed in Sweden

The number of amyloidogenic transthyretin (TTR) mutations described in the literature is more than 100. However, for several mutations, the phenotype has been described in a few individuals only; thus, the knowledge of the clinical course and the outcome after therapeutical interventions such as liver transplantation is limited. We describe the phenotype associated with five rare amyloidogenic TTR mutations that lately were discovered in Sweden: ATTR Val30Leu, Ala45Ser, Leu55Gln, Gly57Arg and Tyr69His of which ATTR Gly57Arg is previously unknown. The symptoms at onset differed, but cardiomyopathy and peripheral neuropathy were observed in all except the ATTR Tyr69His mutation. Likewise, carpal tunnel syndrome was found or had been present in all cases except the case with the ATTR Val30Leu mutation. The phenotype of the ATTR Tyr69His mutation was characterised by oculo-meningeal symptoms with seizures and a steadily progressing dementia, symptoms rarely found in ATTR amyloidosis, but similar to those previously described for this mutation, where all cases appear to originate from one Swedish family. Two patients with the ATTR Leu55Gln and Ala45Ser mutations have been subjected to liver transplantation, but echocardiographic examination has revealed an increasing cardiomyopathy after transplantation in both cases, the ATTR Leu55Gln patient succumbed 2 years after transplantation from progressive disease.

Frequency of the transthyretin Val30Met mutation in the northern Swedish population

Abstract By genotyping a large number of samples from the Northern Sweden Health and Disease Study cohort, a carrier frequency could be determined for the Skellefteå and Lycksele populations. A previous study of the amyloidogenic transthyretin mutation TTRV30M in Northern Sweden’s endemic area has shown a large variation in carrier frequency and penetrance of the trait within the area. However, the estimations have been based on a small sample size within the different regions in the area and therefore, the wide variation in TTRV30M carrier frequency observed between the Lycksele and Skellefteå populations are uncertain. Based on a total of 3460 samples, the estimated overall carrier frequency in the two regions was 1.82% with a carrier frequency in the Skellefteå and Lycksele population of 1.63% and 2.02%, respectively. Thus, the previously reported extremely high frequency in the Lycksele region compared to that of the Skellefteå region could not be substantiated. However, it does not change the previous finding of a surprisingly higher carrier frequency in the population from endemic area of Northern Sweden compared to that reported from endemic areas in Portugal.

Cardiomyopathy in Swedish patients with the Gly53Glu and His88Arg transthyretin variants

We report two new amyloidogenic transthyretin (TTR) variants detected in the Swedish population. One variant was previously unknown, while the other has been described in a French family. In Swedish patients, both variants have caused late-onset cardiac amyloidosis characterised by heart failure. In both cases, the diagnosis was determined by the detection of amyloid deposits in skin and/or rectal biopsies and identification of TTR mutations by genetic analysis. The index case of the previously unknown mutation (ATTR His88Arg) was a 66-year-old Swedish man, who sought medical attention for increasing dyspnea. Echocardiographic examination disclosed a restrictive cardiomyopathy, and subsequent examinations disclosed TTR amyloidosis. The patient is alive with moderate symptoms one year after the onset of disease. The index case for the new Swedish mutation (ATTR Gly53Glu) is a woman who sought medical attention at the age of 57 because of increasing dyspnea. Echocardiographic examination disclosed a hypertrophic cardiomyopathy with diastolic impairment. The diagnosis of systemic amyloidosis was made by fat aspiration biopsy and histopathology. The patient developed severe intractable heart failure, with pulmonary effusion and ascites. She died four years after the onset of her disease of intractable heart and kidney failure. Post mortem examination of biopsy specimens and blood revealed TTR amyloid deposits and the ATTR Gly53Glu mutation was detected.

A Swedish family with the rare Phe33Leu transthyretin mutation

Familial amyloidotic polyneuropathy (FAP) designates TTR mutations where the phenotype is dominated by a peripheral sensory-motor polyneuropathy. The most common mutation is ATTR Val30Met. FAP in association with ATTR Phe33Leu has been described previously in two American families, one of Polish–Lithuanian descent and the other of Polish–American. In this study, we report the phenotype of the ATTR Phe33Leu in a Swedish family. The proband is a 48 year-old patient from northern Sweden, whose father died with symptoms suggestive of FAP. Characteristic clinical features included polyneuropathy, carpal tunnel syndrome and asymptomatic, but echocardiographic examination diagnosed cardiomyopathy. The family history supports an early intervention with orthotopic liver transplantation in patients with FAP associated with the TTR Phe33Leu, and the patient was submitted for liver transplantation.

A novel transthyretin Lys70Glu (p.Lys90Glu) mutation presenting with vitreous amyloidosis and carpal tunnel syndrome

Abstract Objective: We describe a novel TTR mutation with vitreous opacities and carpal tunnel syndrome. Materials and methods: A 78 year-old woman with vitreous opacities, her daughter with dry eye syndrome, and brother with carpal tunnel syndrome were tested for a mutation in the TTR gene. The vitreous opacities were removed and stained with Congo red and immunohistochemistry against wild type TTR. Skin and gut biopsies and specimens of soft tissue were examined histopathologically. Leukocyte DNA from the proband was analysed by direct sequencing of exons 1 to 4 of the TTR gene and DNA from her daughter and brother using segregation analysis. Results: A point mutation c.268 A>C, in the TTR gene, leading to a missense mutation p.Lys90Glu was found in all subjects. The vitreous opacities were pearl string-like. Histopathology showed red to green birefringence in Congo red, typical to amyloid, and the specimens were immunoreactive with antibodies against TTR. Conclusion: We present a novel autosomally inherited Lys90Glu mutation in the TTR gene. This is the first reported FAP family with this mutation in Finland.