Summary Replicative senescence limits the proliferation of somatic cells passaged in culture and may reflect cellular aging in vivo. The most widely used biomarker for senescent and aging cells is senescence‐associated β‐galactosidase (SA‐β‐gal), which is defined as β‐galactosidase activity detectable at pH 6.0 in senescent cells, but the origin of SA‐β‐gal and its cellular roles in senescence are not known. We demonstrate here that SA‐β‐gal activity is expressed from GLB1, the gene encoding lysosomal β‐D‐galactosidase, the activity of which is typically measured at acidic pH 4.5. Fibroblasts from patients with autosomal recessive GM1‐gangliosidosis, which have defective lysosomal β‐galactosidase, did not express SA‐β‐gal at late passages even though they underwent replicative senescence. In addition, late passage normal fibroblasts expressing small‐hairpin interfering RNA that depleted GLB1 mRNA underwent senescence but failed to express SA‐β‐gal. GLB1 mRNA depletion also prevented expression of SA‐β‐gal activity in HeLa cervical carcinoma cells induced to enter a senescent state by repression of their endogenous human papillomavirus E7 oncogene. SA‐β‐gal induction during senescence was due at least in part to increased expression of the lysosomal β‐galactosidase protein. These results also indicate that SA‐β‐gal is not required for senescence.

XPF-ERCC1 endonuclease is required for repair of helix-distorting DNA lesions and cytotoxic DNA interstrand crosslinks. Mild mutations in XPF cause the cancer-prone syndrome xeroderma pigmentosum. A patient presented with a severe XPF mutation leading to profound crosslink sensitivity and dramatic progeroid symptoms. It is not known how unrepaired DNA damage accelerates ageing or its relevance to natural ageing. Here we show a highly significant correlation between the liver transcriptome of old mice and a mouse model of this progeroid syndrome. Expression data from XPF-ERCC1-deficient mice indicate increased cell death and anti-oxidant defences, a shift towards anabolism and reduced growth hormone/insulin-like growth factor 1 (IGF1) signalling, a known regulator of lifespan. Similar changes are seen in wild-type mice in response to chronic genotoxic stress, caloric restriction, or with ageing. We conclude that unrepaired cytotoxic DNA damage induces a highly conserved metabolic response mediated by the IGF1/insulin pathway, which re-allocates resources from growth to somatic preservation and life extension. This highlights a causal contribution of DNA damage to ageing and demonstrates that ageing and end-of-life fitness are determined both by stochastic damage, which is the cause of functional decline, and genetics, which determines the rates of damage accumulation and decline.

We have calculated the relative frequency and the birth prevalence of lysosomal storage diseases (LSDs) in The Netherlands based on all 963 enzymatically confirmed cases diagnosed during the period 1970-1996. The combined birth prevalence for all LSDs is 14 per 100,000 live births. Glycogenosis type II is the most frequent LSD with a birth prevalence of 2.0 per 100,000 live births, representing 17% of all diagnosed cases. Within the group of lipidoses, metachromatic leukodystrophy (MLD) is the most frequent LSD. MLD was diagnosed in 24% of lipidoses and the calculated birth prevalence was 1.42 per 100,000 for all types combined. Krabbe disease, diagnosed in 17% of cases, also belongs to the more frequent lipid storage diseases in The Netherlands with a birth prevalence of 1.35 per 100,000. The birth prevalence of Gaucher disease, commonly regarded as the most frequent lipid storage disease is 1.16 per 100,000 for all types combined. The combined birth prevalence for all lipid storage diseases is 6.2 per 100,000 live births. Within the group of mucopolysaccharidoses (MPSs), MPS I has the highest calculated birth prevalence of 1.19 per 100,000 (25% of all cases of MPS diagnosed), which is slightly more frequent than MPS IIIA with an estimated birth prevalence of 1.16 per 100,000. As a group, MPS III comprises 47% of all MPS cases diagnosed and the combined birth prevalence is 1.89 per 100,000 live births. The birth prevalence of MPS II is 0.67 per 100,000 (1.30 per 100,000 male live births). All other MPSs are rare. The combined birth prevalence for all MPSs is 4.5 per 100,000 live births. Mucolipidoses and oligosaccharidoses are very rare with birth prevalences between 0.04 and 0.20 for individual diseases. Only 49 cases were diagnosed between 1970 and 1996. Their combined birth prevalence is 1.0 per 100,000 live births.

Premature arteriosclerosis and thromboembolic events are well-known complications of homozygous homocystinuria due to cystathionine synthase deficiency. It is unknown whether heterozygosity for homocystinuria predisposes to premature vascular disease. We explored the frequency of excessive homocysteine accumulation after standardized methionine loading in 75 patients presenting with clinical signs of ischemic disease before the age of 50:25 with occlusive peripheral arterial disease, 25 with occlusive cerebrovascular disease, and 25 with myocardial infarction. In seven patients in each of the first two groups but in none of the patients in the third group, heterozygosity for homocystinuria was established on the basis of pathological homocysteinemia after methionine loading and cystathionine synthase deficiency in skin fibroblast cultures. Because the frequency of heterozygosity for homocystinuria in the normal population is 1 in 70 at the most, we conclude that this condition predisposes to the development of premature occlusive arterial disease, causing intermittent claudication, renovascular hypertension, and ischemic cerebrovascular disease.

Juvenile hyaline fibromatosis (JHF) and infantile systemic hyalinosis (ISH) are autosomal recessive conditions characterized by multiple subcutaneous skin nodules, gingival hypertrophy, joint contractures, and hyaline deposition. We previously mapped the gene for JHF to chromosome 4q21. We now report the identification of 15 different mutations in the gene encoding capillary morphogenesis protein 2 (CMG2) in 17 families with JHF or ISH. CMG2 is a transmembrane protein that is induced during capillary morphogenesis and that binds laminin and collagen IV via a von Willebrand factor type A (vWA) domain. Of interest, CMG2 also functions as a cellular receptor for anthrax toxin. Preliminary genotype-phenotype analyses suggest that abrogation of binding by the vWA domain results in severe disease typical of ISH, whereas in-frame mutations affecting a novel, highly conserved cytoplasmic domain result in a milder phenotype. These data (1) demonstrate that JHF and ISH are allelic conditions and (2) implicate perturbation of basement-membrane matrix assembly as the cause of the characteristic perivascular hyaline deposition seen in these conditions.

Restrictive dermopathy (RD) is characterized by intrauterine growth retardation, tight and rigid skin with prominent superficial vessels, bone mineralization defects, dysplastic clavicles, arthrogryposis and early neonatal death. In two patients affected with RD, we recently reported two different heterozygous splicing mutations in the LMNA gene, leading to the production and accumulation of truncated Prelamin A. In other patients, a single nucleotide insertion was identified in ZMPSTE24. This variation is located in a homopolymeric repeat of thymines and introduces a premature termination codon. ZMPSTE24 encodes an endoprotease essential for the post-translational cleavage of the Lamin A precursor and the production of mature Lamin A. However, the autosomal recessive inheritance of RD suggested that a further molecular defect was present either in the second ZMPSTE24 allele or in another gene involved in Lamin A processing. Here, we report new findings in RD linked to ZMPSTE24 mutations. Ten RD patients were analyzed including seven from a previous series and three novel patients. All were found to be either homozygous or compound heterozygous for ZMPSTE24 mutations. We report three novel 'null' mutations as well as the recurrent thymine insertion. In all cases, we find a complete absence of both ZMPSTE24 and mature Lamin A associated with Prelamin A accumulation. Thus, RD is either a primary or a secondary laminopathy, caused by dominant de novo LMNA mutations or, more frequently, recessive null ZMPSTE24 mutations, most of which lie in a mutation hotspot within exon 9. The accumulation of truncated or normal length Prelamin A is, therefore, a shared pathophysiological feature in recessive and dominant RD. These findings have an important impact on our knowledge of the pathophysiology in Progeria and related disorders and will help direct the development of therapeutic approaches.

No abstract

Dihydropyrimidine dehydrogenase (DPD) deficiency is an autosomal recessive disease characterised by thymine-uraciluria in homozygous deficient patients and has been associated with a variable clinical phenotype. In order to understand the genetic and phenotypic basis for DPD deficiency, we have reviewed 17 families presenting 22 patients with complete deficiency of DPD. In this group of patients, 7 different mutations have been identified, including 2 deletions [295-298delTCAT, 1897delC], 1 splice-site mutation [IVS14+1G>A)] and 4 missense mutations (85T>C, 703C>T, 2658G>A, 2983G>T). Analysis of the prevalence of the various mutations among DPD patients has shown that the G-->A point mutation in the invariant splice donor site is by far the most common (52%), whereas the other six mutations are less frequently observed. A large phenotypic variability has been observed, with convulsive disorders, motor retardation and mental retardation being the most abundant manifestations. A clear correlation between the genotype and phenotype has not been established. An altered beta-alanine, uracil and thymine homeostasis might underlie the various clinical abnormalities encountered in patients with DPD deficiency.