Neonatal progeria: increased ratio of progerin to lamin A leads to progeria of the newborn

Hutchinson-Gilford progeria syndrome (HGPS) is an important model disease for premature ageing. Affected children appear healthy at birth, but develop the first symptoms during their first year of life. They die at an average age of 13 years, mostly because of myocardial infarction or stroke. Classical progeria is caused by the heterozygous point mutation c.1824C>T in the LMNA gene, which activates a cryptic splice site. The affected protein cannot be processed correctly to mature lamin A, but is modified into a farnesylated protein truncated by 50 amino acids (progerin). Three more variations in LMNA result in the same mutant protein, but different grades of disease severity. We describe a patient with the heterozygous LMNA mutation c.1821G>A, leading to neonatal progeria with death in the first year of life. Intracellular lamin A was downregulated in the patient's fibroblasts and the ratio of progerin to lamin A was increased when compared with HGPS. It is suggestive that the ratio of farnesylated protein to mature lamin A determines the disease severity in progeria.     

A homozygous ZMPSTE24 null mutation in combination with a heterozygous mutation in the LMNA gene causes Hutchinson-Gilford progeria syndrome (HGPS): insights into the pathophysiology of HGPS

Hutchinson-Gilford progeria syndrome (HGPS) is a rare premature aging disorder normally caused by a spontaneous heterozygous mutation in the LMNA gene that codes for the nuclear lamina protein lamin A. Several enzymes are involved in the processing of its precursor, prelamin A, to the mature lamin A. A functional knockout of one of the enzymes involved in prelamin A processing, the zinc metalloprotease ZMPSTE24, causes an even more severe disorder with early neonatal death described as restrictive dermatopathy (RD). This work describes a HGPS patient with a combined defect of a homozygous loss-of-function mutation in the ZMPSTE24 gene and a heterozygous mutation in the LMNA gene that results in a C-terminal elongation of the final lamin A. Whereas the loss of function mutation of ZMPSTE24 normally results in lethal RD, the truncation of LMNA seems to be a salvage alteration alleviating the clinical picture to the HGPS phenotype. The mutations of our patient indicate that farnesylated prelamin A is the deleterious agent leading to the HGPS phenotype, which gives further insights into the pathophysiology of the disorder.     

A conserved splicing mechanism of the LMNA gene controls premature aging

Hutchinson-Gilford progeria syndrome (HGPS) is a rare genetic disorder phenotypically characterized by many features of premature aging. Most cases of HGPS are due to a heterozygous silent mutation (c.1824C>T; p.Gly608Gly) that enhances the use of an internal 5' splice site (5'SS) in exon 11 of the LMNA pre-mRNA and leads to the production of a truncated protein (progerin) with a dominant negative effect. Here we show that HGPS mutation changes the accessibility of the 5'SS of LMNA exon 11 which is sequestered in a conserved RNA structure. Our results also reveal a regulatory role of a subset of serine-arginine (SR)-rich proteins, including serine-arginine rich splicing factor 1 (SRSF1) and SRSF6, on utilization of the 5'SS leading to lamin A or progerin production and a modulation of this regulation in the presence of the c.1824C>T mutation is shown directly on HGPS patient cells. Mutant mice carrying the equivalent mutation in the LMNA gene (c.1827C>T) also accumulate progerin and phenocopy the main cellular alterations and clinical defects of HGPS patients. RNAi-induced depletion of SRSF1 in the HGPS-like mouse embryonic fibroblasts (MEFs) allowed progerin reduction and dysmorphic nuclei phenotype correction, whereas SRSF6 depletion aggravated the HGPS-like MEF's phenotype. We demonstrate that changes in the splicing ratio between lamin A and progerin are key factors for lifespan since heterozygous mice harboring the mutation lived longer than homozygous littermates but less than the wild-type. Genetic and biochemical data together favor the view that physiological progerin production is under tight control of a conserved splicing mechanism to avoid precocious aging.     

Somatic and gonadal mosaicism in Hutchinson-Gilford progeria

We have studied a patient with Hutchinson-Gilford progeria (HGP). Sequence analysis of the LMNA gene demonstrated the presence of a c.1824 C > T (p.G608G) mutation, activating a cryptic splice donor site and leading to the formation of a truncated Lamin A protein. All molecularly characterized autosomal dominant HGP cases described so far result from de novo LMNA mutations, mostly originating on the paternal allele and are often linked with advanced paternal age. However, in our patient, the mutation was transmitted by the mother who showed somatic and germline mosaicism without HGP manifestations.     

LMNA mutation in progeroid syndrome in association with strokes

Hutchinson-Gilford progeria syndrome is a very rare but well-characterized genetic disorder that causes premature ageing. Clinical features affect growth, skeleton, body fat, skin, hair and the cardiovascular system. It is caused by mutations in LMNA gene, the most frequent being p.Gly608Gly (c.1824C > T) in exon 11.Here we present a four-year-old HGPS patient who presented several severe strokes and carried a heterozygous LMNA missense mutation in exon 2: p.Glu138Lys. This mutation is located far from the C-terminal region implicated in the posttranslational processing of prelamin A, but it lies within the rod domain of lamin A/C that represents a highly conserved domain specific to nuclear lamins. We hypothesize that this region could be involved in early and severe strokes in HGPS, such as those presented by our patient.     

一个常染色体显性遗传Emery-Dreifuss型肌营养不良家系的基因突变分析

目的 探讨一个常染色体显性遗传Emery-Dreifuss型肌营养不良(Emery-Dreifuss muscular dystrophy,EDMD)家系的临床、病理及遗传学特点.方法 收集家系中2例患者(先证者及女儿)的临床资料及骨骼肌标本,行组织化学染色病理分析;收集先证者及家系成员(3代7人)血液DNA标本,采用聚合酶链反应和DNA直接测序方法 对LMNA基因进行突变检测;明确基因变异位点后对家系行单倍型分析.结果 先证者具有典型的EDMD临床表现:关节挛缩、进行性加重的肌无力和肌萎缩、心脏传导异常;骨骼肌活检病理示肌源性合并轻度神经源性改变;2例患者LMNA基因第9外显子发现杂合错义突变1583(C→G)(T528R),表型正常的其他家系成员未发现该突变;单倍型分析显示先证者及女儿具有相同的致病单倍型.结论 报道了中国人常染色体显性遗传EDMD患者的表现型及基因型.     

Functional consequences of an LMNA mutation associated with a new cardiac and non-cardiac phenotype

Heritable dilated cardiomyopathy is a genetically highly heterogeneous disease. To date 17 different chromosomal loci have been described for autosomal dominant forms of dilated cardiomyopathy with or without additional clinical manifestations. Among the 10 mutated genes associated with dilated cardiomyopathy, the lamin A/C (LMNA) gene has been reported in forms associated with conduction-system disease with or without skeletal muscle myopathy. For the first time, we report here a French family affected with a new phenotype composed of an autosomal dominant severe dilated cardiomyopathy with conduction defects or atrial/ventricular arrhythmias, and a specific quadriceps muscle myopathy. In all previously reported cases with both cardiac and neuromuscular involvement, neuromuscular disorders preceded cardiac abnormalities. The screening of the coding sequence of the LMNA gene on all family members was performed and we identified a missense mutation (R377H) in the lamin A/C gene that cosegregated with the disease in the family. Cell transfection experiments showed that the R377H mutation leads to mislocalization of both lamin and emerin. These results were obtained in both muscular (C2C12) and non-muscular cells (COS-7). This new phenotype points out the wide spectrum of neuromuscular and cardiac manifestations associated with lamin A/C mutations, with the functional consequence of this mutation seemingly associated with a disorganization of the lamina.     

An association of Hutchinson-Gilford progeria and malignancy

Mutations in the LMNA gene encoding lamins A/C are responsible for a variety of disorders, commonly referred to as "laminopathies," including the segmental premature aging syndrome Hutchinson-Gilford progeria. We describe in this report the rare association of osteosarcoma and slowly progressing progeria in an 11-year-old girl carrying a truncating heterozygous c.1868C > G (p.T623S) prelamin A mutation. These findings are discussed in light of recent data on the pathophysiological mechanisms underlying progeria and "physiological" aging in human, as well as previous data on other well-known segmental aging syndromes.     

The laminopathies: a clinical review

The laminopathies are a diverse group of conditions caused by mutations in the LMNA gene (MIM*150330). LMNA encodes the nuclear envelope proteins lamin A and lamin C by utilization of an alternative splice site in exon 10. The human LMNA gene was identified in 1986 but it was another 13 years before it was found to be the causative gene for a disease, namely Emery Dreifuss muscular dystrophy. Since then, a further eight clearly defined phenotypes have been associated with LMNA mutations. The diversity of these phenotypes is striking with features such as premature ageing, axonal neuropathy, lipodystrophy and myopathy being seen. These phenotypes and the emerging genotype/phenotype correlations are the subject of this review.     

High prevalence of laminopathies among patients with metabolic syndrome

Constitutional laminopathies, such as the Dunnigan familial partial lipodystrophy, are severe diseases caused by mutations in A-type lamins and share several features with metabolic syndrome (MS). In this study, we hypothesized that MS may be, in some cases, a mild form of laminopathies and use the abnormal cell nucleus phenotype observed in these diseases as a primary screening test in patients suffering from common MS. Nuclear shape and lamin A nucleoplasmic distribution abnormalities were systematically searched in lymphoblastoid cells of 87 consecutive patients with MS. In parallel, five genes encoding either the A-type lamins or the enzymes of the lamin A maturation pathway were systematically sequenced (LMNA, ZMPSTE24, ICMT, FNTA and FNTB). We identified 10 MS patients presenting abnormal nuclear shape and disturbed lamin A/C nuclear distribution. These patients were not clinically different from those without nuclear abnormalities except that they were younger, and had higher triglyceridemia and SGPT levels. Three of them carry a heterozygous mutation in LMNA or in ZMPSTE24, a gene encoding one of the lamin A processing enzymes. All three mutations are novel missense mutations predicted to be damaging. Both lymphoblastoid cells and skin fibroblasts from the patient carrying the mutation in ZMPSTE24, showed accumulation of lamin A precursor, indicating an alteration of the lamin A processing, confirmed by functional study. Together, these results show for the first time, that a significant proportion of MS patients exhibits laminopathies and suggest that systematic investigation of lamin A and its partners should be performed at the diagnosis of this syndrome.     

LMNA messenger RNA expression in highly active antiretroviral therapy-treated HIV-positive patients

The LMNA gene encodes for lamins A and C as major products, which are involved in nuclear stability, chromatin structure, and gene expression. Several LMNA mutations cause an insulin-resistant lipodystrophy that shares features with HIV-related lipodystrophy. Some HIV-treatment agents alter lamin A/C maturation, organization, and stability in 3T3-L1. We aimed to test the hypothesis that human adipose tissue LMNA expression can be altered in highly active antiretroviral therapy (HAART)-treated HIV-positive patients with lipodystrophy. We have also analyzed both isoforms and explored if their expression is associated with insulin resistance or inflammation in these patients. A cross-sectional study that analyzed abdominal subcutaneous adipose tissue from 39 treated HIV-positive patients (25 of whom had lipodystrophy) and 21 uninfected control subjects was performed. We have observed lower levels of lamin A isoform but normal levels of lamin C isoform in all HIV-infected patients, irrespective of the presence or absence of lipodystrophy, which reinforces the idea that an altered lamin A/C ratio could reflect a pathogenic condition. We have also found a correlation between LMNA adipose expression and several cytokine and adipogenic gene markers in HIV-positive patients, regardless of the presence or absence of lipodystrophy. Hence, in the present study, the lower lamin A expression observed in HIV-positive patients is related to HIV itself or to treatments rather than to the presence of lipodystrophy.     

Epidermal expression of the truncated prelamin A causing Hutchinson-Gilford progeria syndrome: effects on keratinocytes, hair and skin

Hutchinson-Gilford progeria syndrome (HGPS) is an accelerated aging disorder caused by point mutation in LMNA encoding A-type nuclear lamins. The mutations in LMNA activate a cryptic splice donor site, resulting in expression of a truncated, prenylated prelamin A called progerin. Expression of progerin leads to alterations in nuclear morphology, which may underlie pathology in HGPS. We generated transgenic mice expressing progerin in epidermis under control of a keratin 14 promoter. The mice had severe abnormalities in morphology of skin keratinocyte nuclei, including nuclear envelope lobulation and decreased nuclear circularity not present in transgenic mice expressing wild-type human lamin A. Primary keratinocytes isolated from these mice had a higher frequency of nuclei with abnormal shape compared to those from transgenic mice expressing wild-type human lamin A. Treatment with a farnesyltransferase inhibitor significantly improved nuclear shape abnormalities and induced the formation of intranuclear foci in the primary keratinocytes expressing progerin. Similarly, spontaneous immortalization of progerin-expressing cultured keratinocytes selected for cells with normal nuclear morphology. Despite morphological alterations in keratinocyte nuclei, mice expressing progerin in epidermis had normal hair grown and wound healing. Hair and skin thickness were normal even after crossing to Lmna null mice to reduce or eliminate expression of normal A-type lamins. Although progerin induces significant alterations in keratinocyte nuclear morphology that are reversed by inhibition of farnesyltransferasae, epidermal expression does not lead to alopecia or other skin abnormalities typically seen in human subjects with HGPS.     

Mutations in the LMNA gene encoding lamin A/C

Very recently, mutations within the LMNA gene on chromosome 1q21.2 were shown to result in forms of muscular dystrophy, conduction-system disease, cardiomyopathy, and partial lipodystrophy. The LMNA gene encodes for the nucleophilic A-type lamins, lamin A and lamin C. These isoforms are generated by different splicing within exon 10 of LMNA. Thus lamin A/C is, besides emerin, the first known nucleophilic protein which plays a role in human disease. To date, 41 different mutations, predominantly missense, in the LMNA gene are known causing variable phenotypes. Twenty-three different mutations of LMNA have so far been shown to cause autosomal-dominant Emery-Dreifuss muscular dystrophy (EDMD2), three mutations were reported to cause limb-girdle muscular dystrophy (LGMD1B), eight mutations are known to result in dilated cardiomyopathy (CMD1A), and seven mutations were reported to cause familial partial lipodystrophy (FPL). The reports of lamin mutations including the corresponding phenotype are of great interest in order to gain insights into the function of lamin A/C. Here we summarize the mutations published to date in LMNA encoding lamin A/C.     

Incomplete processing of mutant lamin A in Hutchinson-Gilford progeria leads to nuclear abnormalities, which are reversed by farnesyltransferase inhibition

Hutchinson-Gilford progeria syndrome (HGPS) is typically caused by mutations in codon 608 (G608G) of the LMNA gene, which activates a cryptic splice site resulting in the in-frame loss of 150 nucleotides from the lamin A message. The deleted region includes a protein cleavage site that normally removes 15 amino acids, including a CAAX box farnesylation site, from the lamin A protein. We investigated the processing of the C-terminus of the mutant protein, 'progerin', and found that it does not undergo cleavage and, indeed, remains farnesylated. The retention of the farnesyl group may have numerous consequences, as farnesyl groups increase lipophilicity and are involved in membrane association and in protein interactions, and is likely to be an important factor in the HGPS phenotype. To further investigate this, we studied the effects of farnesylation inhibition on nuclear phenotypes in cells expressing normal and mutant lamin A. Expression of a GFP-progerin fusion protein in normal fibroblasts caused a high incidence of nuclear abnormalities, as was also seen in HGPS fibroblasts, and resulted in abnormal nuclear localization of GFP-progerin in comparison with the localization pattern of GFP-lamin A. Expression of a GFP-lamin A fusion containing a mutation preventing the final cleavage step, causing the protein to remain farnesylated, displayed identical localization patterns and nuclear abnormalities as in HGPS cells and in cells expressing GFP-progerin. Exposure to a farnesyltransferase inhibitor (FTI), PD169541, caused a significant improvement in the nuclear morphology of cells expressing GFP-progerin and in HGPS cells. These results implicate the abnormal farnesylation of progerin in the cellular phenotype in HGPS cells and suggest that FTIs may represent a therapeutic option for patients with HGPS.     

Rapamycin reverses cellular phenotypes and enhances mutant protein clearance in Hutchinson-Gilford progeria syndrome cells

Hutchinson-Gilford progeria syndrome (HGPS) is a lethal genetic disorder characterized by premature aging. HGPS is most commonly caused by a de novo single-nucleotide substitution in the lamin A/C gene (LMNA) that partially activates a cryptic splice donor site in exon 11, producing an abnormal lamin A protein termed progerin. Accumulation of progerin in dividing cells adversely affects the integrity of the nuclear scaffold and leads to nuclear blebbing in cultured cells. Progerin is also produced in normal cells, increasing in abundance as senescence approaches. Here, we report the effect of rapamycin, a macrolide antibiotic that has been implicated in slowing cellular and organismal aging, on the cellular phenotypes of HGPS fibroblasts. Treatment with rapamycin abolished nuclear blebbing, delayed the onset of cellular senescence, and enhanced the degradation of progerin in HGPS cells. Rapamycin also decreased the formation of insoluble progerin aggregates and induced clearance through autophagic mechanisms in normal fibroblasts. Our findings suggest an additional mechanism for the beneficial effects of rapamycin on longevity and encourage the hypothesis that rapamycin treatment could provide clinical benefit for children with HGPS.     

Coronary artery disease in a Werner syndrome-like form of progeria characterized by low levels of progerin, a splice variant of lamin A

Classical Hutchinson-Gilford progeria syndrome (HGPS) is caused by LMNA mutations that generate an alternatively spliced form of lamin A, termed progerin. HGPS patients present in early childhood with atherosclerosis and striking features of accelerated aging. We report on two pedigrees of adult-onset coronary artery disease with progeroid features, who were referred to our International Registry of Werner Syndrome (WS) because of clinical features consistent with the diagnosis. No mutations were identified in the WRN gene that is responsible for WS, among these patients. Instead, we found two novel heterozygous mutations at the junction of exon 10 and intron 11 of the LMNA gene. These mutations resulted in the production of progerin at a level substantially lower than that of HGPS. Our findings indicate that LMNA mutations may result in coronary artery disease presenting in the fourth to sixth decades along with short stature and a progeroid appearance resembling WS. The absence of early-onset cataracts in this setting should suggest the diagnosis of progeroid laminopathy. This study illustrates the evolving genotype-phenotype relationship between the amount of progerin produced and the age of onset among the spectrum of restrictive dermopathy, HGPS, and atypical forms of WS.     

Compound heterozygosity for mutations in LMNA causes a progeria syndrome without prelamin A accumulation

LMNA-associated progeroid syndromes have been reported with both recessive and dominant inheritance. We report a 2-year-old boy with an apparently typical Hutchinson-Gilford progeria syndrome (HGPS) due to compound heterozygous missense mutations (p.T528M and p.M540T) in LMNA. Both mutations affect a conserved region within the C-terminal globular domain of A-type lamins, defining a progeria hot spot. The nuclei of the patient showed no prelamin A accumulation. In general, the nuclear phenotype did not correspond to that previously described for HGPS. Instead, honeycomb figures predominated and nuclear blebs with reduced/absent expression of B-type lamins could be detected. The healthy heterozygous parents showed similar nuclear changes, although in a smaller percentage of nuclei. Treatment with a farnesylation inhibitor resulted in accumulation of prelamin A at the nuclear periphery, in annular nuclear membrane plaques and in intra/trans-nuclear membrane invaginations. In conclusion, these findings suggest a critical role for the C-terminal globular lamin A/C region in nuclear structure and support a major contribution of abnormal assembly to the progeroid phenotype. In contrast to earlier suggestions, we show that prelamin A accumulation is not the major determinant of the progeroid phenotype.