Search

Laminopathies are a heterogeneous group of LMNA gene alteration-related disorders including muscular dystrophies, peripheral neuropathies, progeria, lipodystrophies, mandibuloacral dysplasia and restrictive dermopathy. We recently identified a family displaying mild skeletal muscle compromise and contractures and complaining of cardiac symptoms associated to a novel mutation consisting in c.388 G/T exon 2 LMNA gene substitution. The aim of the study was to assess the pathogenic effect of this mutation by means of computational experiments. The c.388 G/T mutation is a missense mutation causing the substitution of the amino acid Alanine with Serine in position 130 of the protein sequence of the coiled-coil region of Lamin A rod domain. Computational predictions and molecular dynamic simulation of lamin filaments revealed a 50% reduction in the probability of the sequence adopting a coiled-coil conformation. The present study provides a feasible explanation for the potential pathogenic effect of the novel c.388 G/T exon 2 LMNA gene mutation. The simulation revealed how the mutation alters the flexibility of lamin filaments and likely determines an impairment in the constitution of the coiled-coil structure.

Mutations on the LMNA gene are responsible for an heterogeneous group of diseases. Overlapping syndromes related to LMNA gene alterations have been extensively reported. Study scope is to perform a systematic analysis of the overlapping syndromes so far described and to try to correlate the clinical features to the associated genetic alterations. We evaluated all the dominant overlapping syndromes reported by means of a PubMed search and by the analysis of the main databases containing the pathogenic LMNA gene variations and the associated diseases. Metabolic alterations in association to skeletal and/or cardiac alterations proved to be the most frequent overlap syndrome. Overlapping syndromes are mostly associated to inframe mutations in exons 1, 2, 8 and 9. These data further improve the understanding of the pathogenesis of laminopathies.

Introduction: LMNA gene mutations are associated with cardiac and skeletal muscle alterations. Methods: A cohort of 21 mutated individuals was assessed with clinical and instrumental investigations over the years. Results: The median observation period was 6 years. Cardiac compromise was detected in 16 patients. Bradyarrhythmias were the most frequent manifestations, followed by supraventricular arrhythmias. Two individuals suffered from nonsustained and 1 from sustained ventricular tachyarrhythmias. Dilated cardiomyopathy was detected in 3 patients. Evaluation of the frequencies of the clinical expressions showed a high probability of suffering from analogue heart compromise in study subjects bearing the same LMNA gene mutation. Conclusions: Cardiac involvement represents a very common phenotypic expression of LMNA gene mutation. Subjects sharing common genetic background seem to suffer from analogue pattern of cardiac manifestation. Muscle Nerve 46: 187–192, 2012

Patients with a partial reduction of merosin due to mutations in the laminin-α2 chain gene usually present with a mild form of congenital muscular dystrophy or a limb-girdle-like muscular dystrophy. To our knowledge, cardiac impairment has never been reported in such patients. A longitudinal study of a patient with partial laminin-α2 deficiency secondary to mutations in the LAMA2 gene revealed dilated cardiomyopathy with ventricular arrhythmias. Is this a chance association or a novel phenotype?

Introduction: Familial dilated cardiomyopathy with conduction system defects variably associated with skeletal muscle abnormalities is frequently caused by LMNA gene mutations. Methods: A family affected by cardiac abnormalities, either isolated or variably associated with skeletal muscle compromise, was identified. LMNA gene analysis was applied to all family members. Results: A novel intron 5 (c.937-11 C>G) mutation was identified. mRNA transcription analysis was subsequently performed, and cDNA was obtained from mutated patients. It displayed an aberrant splice product featuring the insertion of 40 nucleotides from intron 5, leading to a frameshift. Computational predictions identified a cryptic splice site 40 bp upstream from the canonical site; this alternative splicing event was elicited by intronic mutation, which seems to interfere with the polypyrimidine tract of the canonical site. Conclusions: We have described the first mutation on the LMNA gene interfering with the polypyrimidine tract. Our findings underline the importance of including introns in the search for mutations. Muscle Nerve, 2011

Laminopathies are a heterogeneous group of LMNA-gene-mutation-related clinical disorders associated with alterations of cardiac and skeletal muscle and peripheral nerves, metabolic defects, and premature aging. Leg muscle imaging investigations were performed in a cohort of patients with LMNA gene alterations who were suffering from Emery-Dreifuss muscular dystrophy, limb-girdle muscular dystrophy type 1B, isolated cardiac disorders or a phenotype of cardiac disorders, and lipodystrophy, including one individual with peripheral neuropathy. Leg muscle imaging revealed varying degrees of alteration in the soleus and medial head of gastrocnemius in each subject. This study demonstrates that LMNA-gene-mutated patients devoid of any clinically detectable skeletal muscle involvement have the same pattern of leg muscle involvement as patients with overt skeletal muscle compromise. This finding suggests the presence of a continuum of skeletal muscle involvement among phenotypes of LMNA-gene-mutation-related skeletalmyopathy and cardiomyopathy.

The aim of this study is to report the evolution of a phenotype in members of a single family carrying the heterozygous exon 1 c.178 C/G, p.Arg 60 Gly LMNA gene mutation. All mutated family members underwent neurological and cardiological assessments for a period ranging from 10 to 20 years. At onset, 4 affected adult members presented a phenotype that required pacemaker implantation. Three subjects underwent cardiac transplantation leading to long-term survival in 2 of them. One of the 3 longest surviving relatives manifested late lipodystrophy, and the other 2 had lipodystrophy, insulin-resistant diabetes, and distal peripheral neuropathy. The findings demonstrate that the exon 1 c.178 C/G, p.Arg 60 Gly LMNA gene mutation is associated with a novel phenotype featuring cardiac involvement followed by late lipodystrophy, diabetes, and peripheral axonal neuropathy.

Background The Mediterranean island of Sardinia has a strikingly high incidence of the autoimmune disorders Type 1 Diabetes (T1D) and Multiple Sclerosis (MS). Furthermore, the two diseases tend to be co-inherited in the same individuals and in the same families. These observations suggest that some unknown autoimmunity variant with relevant effect size could be fairly common in this founder population and could be detected using linkage analysis. Methods To search for T1D and MS loci as well as any that predispose to both diseases, we performed a whole genome linkage scan, sequentially genotyping 593 microsatellite marker loci in 954 individuals distributed in 175 Sardinian families. In total, 413 patients were studied; 285 with T1D, 116 with MS and 12 with both disorders. Model-free linkage analysis was performed on the genotyped samples using the Kong and Cox logarithm of odds (LOD) score statistic. Results In T1D, aside from the HLA locus, we found four regions showing a lod-score ≥1; 1p31.1, 6q26, 10q21.2 and 22q11.22. In MS we found three regions showing a lod-score ≥1; 1q42.2, 18p11.21 and 20p12.3. In the combined T1D-MS scan for shared autoimmunity loci, four regions showed a LOD >1, including 6q26, 10q21.2, 20p12.3 and 22q11.22. When we typed more markers in these intervals we obtained suggestive evidence of linkage in the T1D scan at 10q21.2 (LOD = 2.1), in the MS scan at 1q42.2 (LOD = 2.5) and at 18p11.22 (LOD = 2.6). When all T1D and MS families were analysed jointly we obtained suggestive evidence in two regions: at 10q21.1 (LOD score = 2.3) and at 20p12.3 (LOD score = 2.5). Conclusion This suggestive evidence of linkage with T1D, MS and both diseases indicates critical chromosome intervals to be followed up in downstream association studies.

The case of a family in which several members displayed conduction defects inherited as a dominant trait is reported. The proband was a young woman with a 1st degree atrio-ventricular block and high serum creatine kinase. Several members of the family featured cardiologic symptoms. All adult family members were clinically evaluated and blood tests including serum creatine-kinase levels, standard and Holter ECG, echocardiogram and muscle MRI were performed. LMNA gene analysis was carried out and a novel missense mutation consisting in substitution of exon 4 c.799 T/C, p.Tyr267His was revealed. The mutation was present in seven family members, five of whom displayed cardiac defects alone with no involvement of the skeletal muscle. In all mutated individuals muscle MRI featured a pattern of skeletal muscle involvement similar to that observed in autosomal dominant Emery Dreifuss muscular dystrophy, suggesting that even patients bearing a LMNA gene mutation associated to an apparently selective cardiac phenotype may present subclinical skeletal muscle involvement.

Lamins are the principal components of the nuclear lamina, a network constituting the major structural framework of the nuclear envelope. Alterations in lamin A/C have been associated with a heterogeneous series of human disorders known as laminopathies. We report the finding of a novel deletion in the central rod domain of lamin A/C exon 3 gene in four members of the same family. This genetic alteration was likely responsible for the relatively homogeneous clinical phenotype observed in our three patients, represented by a prominent cardiac conduction-system disease necessitating permanent pacemaker implantation, and limited skeletal involvement manifested by spinal rigidity and contractures. The findings from these cases further expand the clinical spectrum associated with mutations in the LMNA gene.

A linkage and association of the CD45 (protein-tyrosine phosphatase, receptor-type C) C77G polymorphism and multiple sclerosis (MS) has been found in some studies but not in others. We analysed the C77G polymorphism in MS patients from the genetically homogeneous population of Sardinia. Using the transmission disequilibrium test, the mutation has been sought in 241 patients and 217 healthy sibs (HS) from singleton MS families and it was found in 5 (2.07 %) affected and 3 (1.38%) HS from 7 heterozygous parents (1.45 %). Transmission of the G77 allele was 71.4 % (TDT = 1.3, P = 0.26) in patients and 50% (TDT = 0, P = 1) in HS. Stratifying families according to carriage of MS-predisposing (DR+) or not-predisposing (DR–) HLA-DR-DQ genotype in patients, percentage of G77 transmission to DR+ patients was 33 (TDT = 0.33, P = 0.56, Pc = 1.12), while it was 100 (TDT = 4, P = 0.045, Pc = 0.09) in the DR-patients. We concluded that, despite the presence of CD45 G77 polymorphism in a few patients who did not carry the HLADR- DQ MS-predisposing molecules, CD45 did not contribute to development of the disease in Sardinian MS.

The prevalence of multiple sclerosis in Sardinia is significantly higher than in neighbouring Mediterranean countries, suggesting that the isolated growth of the population has concentrated genetic factors which increase susceptibility to the disease. The distinct HLA association of multiple sclerosis in Sardinia supports this interpretation. We have performed a whole genome screen for linkage in 49 Sardinian multiplex families using 327 markers. Non parametric linkage analysis of these data reveal suggestive linkage in the region of Chr 1q31, Chr 10q23 and Chr 11p15.

Several studies have indicated that multiple sclerosis (MS) is associated and linked to the major histocompatibility complex (MHC)/human leukocyte antigen (HLA) region of chromosome 6p21.3, but the exact location and nature of the primarily associated locus within the HLA complex is still controversial and largely presumptive. By linkage disequilibrium mapping, we have systematically investigated this chromosome region in the founder population of Sardinia to determine the relative associations of the various loci with MS. An overall 11.4 Mb region, which encompasses the whole HLA complex, was scanned with 19 microsatellite markers and with single nucleotide polymorphisms within 12 functional candidate genes and assessed for MS association using the extended transmission disequilibrium test (ETDT). A peak of association represented by the three adjacent DRB1, -DQA1 and -DQB1 loci was detected in the class II region. Two additional less significant areas of association were detected, respectively, in the centromeric side of the class II region at the DPB1 locus and, telomeric of the classically defined class I loci, at the D6S1683 microsatellite. Conditional ETDT analysis indicated that these regions of association could be independent of each other. Within the main peak of association, DRB1 and DQB1 contribute to the disease association independently of each other whereas DQA1 had no detectable primary genetic effects. We evaluated the haplotype distribution at the region showing the strongest association and found five DQB1-DRB1 haplotypes positively associated with MS in Sardinia. These consistently included all the haplotypes previously found associated with MS in the various human populations, thus supporting a primary effect of the products of these loci in MS. Overall these results are consistent with a multilocus model of the MHC encoded susceptibility to MS.