Maria Rosaria D'Apice

Atypical Progeroid Syndrome due to Heterozygous Missense LMNA Mutations

CONTEXT Hutchinson-Gilford progeria syndrome (HGPS) and mandibuloacral dysplasia are well-recognized allelic autosomal dominant and recessive progeroid disorders, respectively, due to mutations in lamin A/C (LMNA) gene. Heterozygous LMNA mutations have also been reported in a small number of patients with a less well-characterized atypical progeroid syndrome (APS). OBJECTIVE The objective of the study was to investigate the underlying genetic and molecular basis of the phenotype of patients presenting with APS. RESULTS We report 11 patients with APS from nine families, many with novel heterozygous missense LMNA mutations, such as, P4R, E111K, D136H, E159K, and C588R. These and previously reported patients now reveal a spectrum of clinical features including progeroid manifestations such as short stature, beaked nose, premature graying, partial alopecia, high-pitched voice, skin atrophy over the hands and feet, partial and generalized lipodystrophy with metabolic complications, and skeletal anomalies such as mandibular hypoplasia and mild acroosteolysis. Skin fibroblasts from these patients when assessed for lamin A/C expression using epifluorescence microscopy revealed variable nuclear morphological abnormalities similar to those observed in patients with HGPS. However, these nuclear abnormalities in APS patients could not be rescued with 48 h treatment with farnesyl transferase inhibitors, geranylgeranyl transferase inhibitors or trichostatin-A, a histone deacetylase inhibitor. Immunoblots of cell lysates from fibroblasts did not reveal prelamin A accumulation in any of these patients. CONCLUSIONS APS patients have a few overlapping but some distinct clinical features as compared with HGPS and mandibuloacral dysplasia. The pathogenesis of clinical manifestations in APS patients seems not to be related to accumulation of mutant farnesylated prelamin A.

Autophagic degradation of farnesylated prelamin A as a therapeutic approach to lamin-linked progeria

Farnesylated prelamin A is a processing intermediate produced in the lamin A maturation pathway. Accumulation of a truncated farnesylated prelamin A form, called progerin, is a hallmark of the severe premature ageing syndrome, Hutchinson-Gilford progeria. Progerin elicits toxic effects in cells, leading to chromatin damage and cellular senescence and ultimately causes skin and endothelial defects, bone resorption, lipodystrophy and accelerated ageing. Knowledge of the mechanism underlying prelamin A turnover is critical for the development of clinically effective protein inhibitors that can avoid accumulation to toxic levels without impairing lamin A/C expression, which is essential for normal biological functions. Little is known about specific molecules that may target farnesylated prelamin A to elicit protein degradation. Here, we report the discovery of rapamycin as a novel inhibitor of progerin, which dramatically and selectively decreases protein levels through a mechanism involving autophagic degradation. Rapamycin treatment of progeria cells lowers progerin, as well as wild-type prelamin A levels, and rescues the chromatin phenotype of cultured fibroblasts, including histone methylation status and BAF and LAP2α distribution patterns. Importantly, rapamycin treatment does not affect lamin C protein levels, but increases the relative expression of the prelamin A endoprotease ZMPSTE24. Thus, rapamycin, an antibiotic belonging to the class of macrolides, previously found to increase longevity in mouse models, can serve as a therapeutic tool, to eliminate progerin, avoid farnesylated prelamin A accumulation, and restore chromatin dynamics in progeroid laminopathies.

The etiology of acute recurrent pancreatitis in children: A challenge for pediatricians

Objectives: To assess specific etiologies of acute recurrent pancreatitis at a single Italian pediatric cystic fibrosis (CF) center. Methods: We studied, retrospectively, 78 young patients (39 female subjects; mean age at diagnosis, 8.8 ± 5.1 years) affected by acute recurrent episodes of pancreatitis, remained etiologically undiagnosed at first-level assessment. All patients were submitted to endoscopic retrograde cholangiopancreatography to exclude biliopancreatic malformations and tested for CF by a sweat chloride test. Most patients also were studied for the research of CFTR, PRSS1, and SPINK1 gene mutations. Results: A high percentage of family history for chronic pancreatitis was observed (20.5%). The sweat test identified 8 subjects (10.3%) with classic CF (2 patients) or at risk for CF (6 patients). Genetic analysis showed mutations in CFTR, SPINK1, and PRSS1 genes in 39.6%, 7.1%, and 4.5% of patients, respectively. A biliopancreatic malformation was diagnosed in 15 patients (19.2%). We also observed biliary lithiasis (5 patients [6.5%]), congenital pancreatic polycystosis (2 patients), a case of dyslipidemia, and 1 patient with a posttransplantation, drug-induced pancreatitis. Conclusions: Recurrent pancreatitis in children has several etiologies. Genetic testing confirms the high frequency of CFTR mutations. This suggests that it is of some value to identify patients with late-onset CF and CFTR-related disorders.

CARD15 mutation analysis in an Italian population: Leu1007fsinsC but neither Arg702Trp nor Gly908Arg mutations are associated with Crohn's disease

BackgroundCARD15 gene mutations have been demonstrated to confer a high risk of Crohn’s disease (CD). Despite this, recent studies reported variable associations between CD and CARD15 mutations in distinct ethnic groups, thus raising the hypothesis that genetic and/or allelic heterogeneity may influence the relationship between CARD15 and CD. The purpose of this study was to evaluate the frequency of the main mutations of the CARD15 gene (Leu1007fsinsC, Arg702Trp, and Gly908Arg) in Italian CD patients and to establish possible genotype-phenotype correlations. MethodsOne hundred sixty-five CD patients and 125 healthy subjects were consecutively enrolled from January to November 2001. The Leu1007fsinsC mutation was assessed by denaturing high-performance liquid chromatography and Arg702Trp and Gly908Arg mutations by Pyrosequencing technology. ResultsAmong the CARD15 gene mutations tested, only the Leu1007fsinsC was associated with CD (30/165 CD patients, 18%, versus 3/125 healthy subjects, 2.4%; p < 0.001). In particular, 23 CD patients were heterozygotes and 7 were homozygotes. No healthy subject exhibited the mutant homozygous genotype. Odds ratios for CD were 6.9 for heterozygotes and 41.0 for homozygotes. The genotype-phenotype analysis revealed that a fibrostenosing CD of the distal ileum was more frequent in patients carrying the Leu1007fsinsC mutation. ConclusionsThis study confirms the association between CARD15 gene mutations and CD and shows that only the Leu1007fsinsC mutation is a risk factor of CD in an Italian population.

Epidemiology and a novel procedure for large scale analysis of CFTR rearrangements in classic and atypical CF patients: A multicentric Italian study

BACKGROUND Mutation epidemiology in each ethnic group is a crucial step of strategies for cystic fibrosis (CF) diagnosis and counselling. To date, the scanning of the whole coding region of the cystic fibrosis transmembrane conductance regulator (CFTR) gene permits to identify about 90% of alleles from patients bearing CF and a lower percentage in patients bearing atypical CF. CFTR rearrangements in heterozygosis elude current techniques for molecular analysis, and some of them have been reported with a frequency up to 6% in various ethnic groups. METHODS Using quantitative PCR analysis of all coding regions, we assessed the occurrence of CFTR rearrangements in 130 alleles from classic CF patients and in 198 alleles from atypical CF patients (all unrelated and from Italian descent) bearing unidentified mutations after the scanning of CFTR. RESULTS Seven rearrangements (i.e., dele1, dele2, dele2_3, dele 14b_17b, dele17a_18, dele22_23, and dele22_24) were identified in 34/131 (26.0%) CF alleles bearing undetected mutations (which means about 2.5% of all CF alleles) and in none of the 198 alleles from atypical CF. The CFTR haplotype and the sequence analysis of the breakpoints confirmed the common origin of all the rearrangements. Thus, we set up a novel duplex PCR assay for the large-scale analysis of the seven rearrangements. The procedure was rapid (all PCR amplifications were obtained under the same conditions), costless and repeatable. CONCLUSIONS It is useful to select the CFTR rearrangements more frequent in specific ethnic groups and to set up procedures for large-scale analysis. Their study can be performed in cases in which a high detection rate is required (i.e., partners of CF carriers/patients). On the contrary, the analysis of rearrangement is useless in atypical CF patients.

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.

Molecular analysis using DHPLC of cystic fibrosis: increase of the mutation detection rate among the affected population in Central Italy.

BackgroundCystic fibrosis (CF) is a multisystem disorder characterised by mutations of the CFTR gene, which encodes for an important component in the coordination of electrolyte movement across of epithelial cell membranes. Symptoms are pulmonary disease, pancreatic exocrine insufficiency, male infertility and elevated sweat concentrations. The CFTR gene has numerous mutations (>1000) and functionally important polymorphisms (>200). Early identification is important to provide appropriate therapeutic interventions, prognostic and genetic counselling and to ensure access to specialised medical services. However, molecular diagnosis by direct mutation screening has proved difficult in certain ethnic groups due to allelic heterogeneity and variable frequency of causative mutations.MethodsWe applied a gene scanning approach using DHPLC system for analysing specifically all CFTR exons and characterise sequence variations in a subgroup of CF Italian patients from the Lazio region (Central Italy) characterised by an extensive allelic heterogeneity.ResultsWe have identified a total of 36 different mutations representing 88% of the CF chromosomes. Among these are two novel CFTR mutations, including one missense (H199R) and one microdeletion (4167delCTAAGCC).ConclusionUsing this approach, we were able to increase our standard power rate of mutation detection of about 11% (77% vs. 88%).

The R527H mutation in LMNA gene causes an increased sensitivity to ionizing radiation.

Mandibuloacral dysplasia type A (MADA; OMIM # 248370) is a premature ageing disease caused by the homozygous R527H mutation in the LMNA gene. At the cellular level, MADA is characterized by unprocessed prelamin A accumulation, nuclear architecture alterations, chromatin defects and increased incidence of apoptosis. In some progeroid laminopathies (e.g. HGPS) it has been demonstrated that such biochemical and morphological alterations are strongly linked with genomic instability. To test this also in MADA fibroblasts, their response to the ionising radiation- induced damage was analysed. We observed that their ability to repair the damage was significantly impaired, as demonstrated by the increased chromosome damage and the higher percentage of residual γ-H2AX foci, corresponding to unrepaired DNA-damage sites. Moreover, MADA fibroblasts showed a markedly reduced phosphorylation of p53 at Ser15(S15) and a lower induction of p53 and CDKN1A proteins after irradiation, compared to the control cell line. Upon irradiation, we also detected differences in the expression of some p53 downstream target genes. In addition, MADA cells showed partial defects in the checkpoint response, particularly in G1/S transition. Our results indicate that accumulation of the lamin A precursor protein determines a defect in DNA damage response after X-ray exposure, supporting a crucial role of lamin A in regulating DNA repair process and cell cycle control.

Rapid scanning of myotubularin (MTM1) gene by denaturing high-performance liquid chromatography (DHPLC)

X-linked myotubular myopathy (XLMTM; OMIM# 310400) is a severe congenital muscle disease caused by mutations in the myotubularin (MTM1) gene. This gene encodes for a lipid phosphatase belonging to a large gene family involved in the regulation of phosphatidylinositide-3-kinase (PI 3-kinase) pathway and membrane trafficking. To date, more than 130 different mutations, distributed in all exons, have been identified in a large number of families. The majority of MTM1 mutations are private and rare, generating high allelic diversity, with a restricted number of recurrent mutations. We set up and formatted a denaturing high performance liquid chromatography (DHPLC) method to allow high throughput, greater accuracy and high resolution in detecting myotubularin mutations. The entire coding sequence of the gene was screened in 10 XLMTM patients using this technique. We identified seven mutated alleles [R37X, (137-11) A, (592-593) insA, T197I, R253X, G378R, G402R] previously characterised by SSCP and DNA sequencing, plus two novel mutations which are reported here [P199S, (1644+2) insG]. In addition we detected a common polymorphism within intron 11 (1314+3A/G). Our results suggest that denaturing high-performance liquid chromatography provides an accurate method for the rapid identification of MTM1 mutations.

Skeletal phenotype of mandibuloacral dysplasia associated with mutations in ZMPSTE24

Mandibuloacral dysplasia (MAD) is a rare recessively inherited premature aging disease characterized by skeletal and metabolic anomalies. It is part of the spectrum of diseases called laminopathies and results from mutations in genes regulating the synthesis of the nuclear laminar protein, lamin A. Homozygous or compound heterozygous mutations in the LMNA gene, which encodes both the precursor protein prelamin A and lamin C, are the commonest cause of MAD type A. In a few cases of MAD type B, mutations have been identified in the ZMPSTE24 gene encoding a zinc metalloproteinase important in the post-translational modification of lamin A. Here we describe a new case of MAD resulting from compound heterozygote mutations in ZMPSTE24 (p.N256S/p.Y70fs). The patient had typical skeletal changes of MAD, but in addition a number of unusual skeletal features including neonatal tooth eruption, amorphous calcific deposits, submetaphyseal erosions, vertebral beaking, severe cortical osteoporosis and delayed fracture healing. Treatment with conventional doses of pamidronate improved estimated volumetric bone density in the spine but did not arrest cortical bone loss. We reviewed the literature on cases of MAD associated with proven LMNA and ZMPSTE24 mutations and found that the unusual features described above were all substantially more prevalent in patients with mutations in ZMPSTE24 than in those with LMNA mutations. We conclude that MAD associated with ZMPSTE24 mutations has a more severe phenotype than that associated with LMNA mutations--probably reflecting the greater retention of unprocessed farnesylated prelamin A in the nucleus, which is toxic to cells.