Novel frameshifting mutations of the ZMPSTE24 gene in two siblings affected with restrictive dermopathy and review of the mutations described in the literature

An exceptional biallelic N-terminal frame shift mutation in ZMPSTE24 leads to non-lethal progeria due to possible utilization of a downstream alternative start codon

Biallelic mutations in ZMPSTE24 are known to be associated with autosomal recessive mandibuloacral dysplasia with type B lipodystrophy (MADB) and lethal restrictive dermopathy (RD), respectively. Disease manifestation is depending on the remaining enzyme activity of the mutated ZMPSTE24 protein. To date, complete loss of function has exclusively been reported in RD cases. In this study, we identified a novel N-terminal homozygous frameshift mutation (c.28_29insA) in a consanguineous family segregating with MADB. An in-depth analysis of the mutated sequence revealed, that the one base pair insertion creates a novel downstream in-frame start codon, which supposedly serves as an alternative translation initiation site (TIS). This possible rescue mechanism would explain the relatively mild clinical outcome in the studied individuals. Our findings demonstrate the necessity for careful interpretation of N-terminal variants potentially effecting translation initiation.

Restrictive dermopathy: Three new patients with ZMPSTE24 mutations and a review of the literature

Restrictive dermopathy (RD) is a rare and lethal laminopathy caused by mutations in LMNA or ZMPSTE24. This series reports 3 patients with RD and reviews the literature of the 113 previously reported cases, including highlights of the unique constellation of clinical findings in RD, as well as histologic, radiographic, and genetic features. Early recognition of these characteristic features is vital to establish a prompt diagnosis and provide adequate family counseling for this terminal condition.

Lamin A as a Determinant of Mechanical Properties of the Cell Nucleus in Health and Disease

One of the main factors associated with worse prognosis in oncology is metastasis, which is based on the ability of tumor cells to migrate from the primary source and to form secondary tumors. The search for new strategies to control migration of metastatic cells is one of the urgent issues in biomedicine. One of the strategies to stop spread of cancer cells could be regulation of the nuclear elasticity. Nucleus, as the biggest and stiffest cellular compartment, determines mechanical properties of the cell as a whole, and, hence, could prevent cell migration through the three-dimensional extracellular matrix. Nuclear rigidity is maintained by the nuclear lamina, two-dimensional network of intermediate filaments in the inner nuclear membrane (INM). Here we present the most significant factors defining nucleus rigidity, discuss the role of nuclear envelope composition in the cell migration, as well consider possible approaches to control lamina composition in order to change plasticity of the cell nucleus and ability of the tumor cells to metastasize.

Defining substrate requirements for cleavage of farnesylated prelamin A by the integral membrane zinc metalloprotease ZMPSTE24

The integral membrane zinc metalloprotease ZMPSTE24 plays a key role in the proteolytic processing of farnesylated prelamin A, the precursor of the nuclear scaffold protein lamin A. Failure of this processing step results in the accumulation of permanently farnesylated forms of prelamin A which cause the premature aging disease Hutchinson-Gilford Progeria Syndrome (HGPS), as well as related progeroid disorders, and may also play a role in physiological aging. ZMPSTE24 is an intriguing and unusual protease because its active site is located inside of a closed intramembrane chamber formed by seven transmembrane spans with side portals in the chamber permitting substrate entry. The specific features of prelamin A that make it the sole known substrate for ZMPSTE24 in mammalian cells are not well-defined. At the outset of this work it was known that farnesylation is essential for prelamin A cleavage in vivo and that the C-terminal region of prelamin A (41 amino acids) is sufficient for recognition and processing. Here we investigated additional features of prelamin A that are required for cleavage by ZMPSTE24 using a well-established humanized yeast system. We analyzed the 14-residue C-terminal region of prelamin A that lies between the ZMPSTE24 cleavage site and the farnesylated cysteine, as well 23-residue region N-terminal to the cleavage site, by generating a series of alanine substitutions, alanine additions, and deletions in prelamin A. Surprisingly, we found that there is considerable flexibility in specific requirements for the length and composition of these regions. We discuss how this flexibility can be reconciled with ZMPSTE24’s selectivity for prelamin A.

Site specificity determinants for prelamin A cleavage by the zinc metalloprotease ZMPSTE24

The integral membrane zinc metalloprotease ZMPSTE24 is important for human health and longevity. ZMPSTE24 performs a key proteolytic step in maturation of prelamin A, the farnesylated precursor of the nuclear scaffold protein lamin A. Mutations in the genes encoding either prelamin A or ZMPSTE24 that prevent cleavage cause the premature aging disease Hutchinson–Gilford progeria syndrome (HGPS) and related progeroid disorders. ZMPSTE24 has a novel structure, with seven transmembrane spans that form a large water-filled membrane chamber whose catalytic site faces the chamber interior. Prelamin A is the only known mammalian substrate for ZMPSTE24; however, the basis of this specificity remains unclear. To define the sequence requirements for ZMPSTE24 cleavage, we mutagenized the eight residues flanking the prelamin A scissile bond (TRSY↓LLGN) to all other 19 amino acids, creating a library of 152 variants. We also replaced these eight residues with sequences derived from putative ZMPSTE24 cleavage sites from amphibian, bird, and fish prelamin A. Cleavage of prelamin A variants was assessed using an in vivo yeast assay that provides a sensitive measure of ZMPSTE24 processing efficiency. We found that residues on the C-terminal side of the cleavage site are most sensitive to changes. Consistent with other zinc metalloproteases, including thermolysin, ZMPSTE24 preferred hydrophobic residues at the P1’ position (Leu647), but in addition, showed a similar, albeit muted, pattern at P2’. Our findings begin to define a consensus sequence for ZMPSTE24 that helps to clarify how this physiologically important protease functions and may ultimately lead to identifying additional substrates.

Premature aging disorders: A clinical and genetic compendium

Progeroid disorders make up a heterogeneous group of very rare hereditary diseases characterized by clinical signs that often mimic physiological aging in a premature manner. Apart from Hutchinson-Gilford progeria syndrome, one of the best-investigated progeroid disorders, a wide spectrum of other premature aging phenotypes exist, which differ significantly in their clinical presentation and molecular pathogenesis. Next-generation sequencing (NGS)-based approaches have made it feasible to determine the molecular diagnosis in the early stages of a disease. Nevertheless, a broad clinical knowledge on these disorders and their associated symptoms is still fundamental for a comprehensive patient management and for the interpretation of variants of unknown significance from NGS data sets. This review provides a detailed overview on characteristic clinical features and underlying molecular genetics of well-known as well as only recently identified premature aging disorders and also highlights novel findings towards future therapeutic options.

Neonatal presentation of COG6-CDG with prominent skin phenotype

Many of the genetic childhood disorders leading to death in the perinatal period follow autosomal recessive inheritance and bear specific challenges for genetic counseling and prenatal diagnostics. Often, affected children die before a genetic diagnosis can be established, thereby precluding targeted carrier testing in parents and prenatal or preimplantation genetic diagnosis in further pregnancies. The clinical phenotype of congenital disorders of glycosylation (CDG) is very heterogeneous and ranges from relatively mild symptoms to severe multisystem dysfunction and even a fatal course. A very rare subtype, COG6-CDG, is caused by deficiency of subunit 6 of the conserved oligomeric Golgi complex and is usually characterized by growth retardation, developmental delay, microcephaly, liver and gastrointestinal disease, joint contractures and episodic fever. It has been proposed that a distinctive feature of COG6-CDG can be ectodermal signs such as hypohidrosis/hyperthermia, hyperkeratosis and tooth anomalies. In a Greek family, who had lost two children in the neonatal period, with prominent skin features initially resembling restrictive dermopathy, severe arthrogryposis, respiratory insufficiency and a rapid fatal course trio whole-exome sequencing revealed the homozygous nonsense mutation c.511C>T, p.(Arg171*) in the COG6 gene. Skin manifestations such as dry skin and hyperkeratosis have been reported in only five out of the 21 reported COG6-CDG cases so far, including two patients with the c.511C>T variant in COG6 but with milder ectodermal symptoms. Our case adds to the phenotypic spectrum of COG6-CDG with prominent ectodermal manifestations at birth and underlines the importance of considering CDG among the possible causes for congenital syndromic genodermatoses.

Restrictive Dermopathy - A Rare Congenital Skin Disorder

Restrictive dermopathy is a rare, autosomal recessive, lethal congenital skin disorder. This congenital genodermatosis could be mistaken for various other similar skin disorders. Diagnosis is a must in the context of genetic counseling for the subsequent pregnancy. We herein report a preterm male neonate with restrictive dermopathy, with additional feature of multiple bone fractures.

Pena-Shokeir syndrome: current management strategies and palliative care

Pena-Shokeir syndrome (PSS) type 1, also known as fetal akinesia deformation sequence, is a rare genetic syndrome that almost always results in intrauterine or early neonatal death. It is characterized by markedly decreased fetal movements, intrauterine growth restriction, joint contractures, short umbilical cord, and features of pulmonary hypoplasia. Antenatal diagnosis can be difficult. Ultrasound features are varied and may overlap with those of Trisomy 18. The poor prognosis of PSS is due to pulmonary hypoplasia, which is an important feature that distinguishes PSS from arthrogryposis multiplex congenital without pulmonary hypoplasia, which has a better prognosis. If diagnosed in the antenatal period, a late termination of pregnancy can be considered following ethical discussion (if the law allows). In most cases, a diagnosis is only made in the neonatal period. Parents of a baby affected with PSS require detailed counseling that includes information on the imprecise recurrence risks and a plan for subsequent pregnancies.

Laminopathies; Mutations on single gene and various human genetic diseases

Lamin A and its alternative splicing product Lamin C are the key intermediate filaments (IFs) of the inner nuclear membrane intermediate filament. Lamin A/C forms the inner nuclear mesh with Lamin B and works as a frame with a nuclear shape. In addition to supporting the function of nucleus, nuclear lamins perform important roles such as holding the nuclear pore complex and chromatin. However, mutations on the Lamin A or Lamin B related proteins induce various types of human genetic disorders and diseases including premature aging syndromes, muscular dystrophy, lipodystrophy and neuropathy. In this review, we briefly overview the relevance of genetic mutations of Lamin A, human disorders and laminopathies. We also discuss a mouse model for genetic diseases. Finally, we describe the current treatment for laminopathies. [BMB Reports 2018; 51(7): 327-337].

Myotonic Dystrophy-A Progeroid Disease?

Myotonic dystrophies (DM) are slowly progressing multisystemic disorders caused by repeat expansions in the DMPK or CNBP genes. The multisystemic involvement in DM patients often reflects the appearance of accelerated aging. This is partly due to visible features such as cataracts, muscle weakness, and frontal baldness, but there are also less obvious features like cardiac arrhythmia, diabetes or hypogammaglobulinemia. These aging features suggest the hypothesis that DM could be a segmental progeroid disease. To identify the molecular cause of this characteristic appearance of accelerated aging we compare clinical features of DM to “typical” segmental progeroid disorders caused by mutations in DNA repair or nuclear envelope proteins. Furthermore, we characterize if this premature aging effect is also reflected on the cellular level in DM and investigate overlaps with “classical” progeroid disorders. To investigate the molecular similarities at the cellular level we use primary DM and control cell lines. This analysis reveals many similarities to progeroid syndromes linked to the nuclear envelope. Our comparison on both clinical and molecular levels argues for qualification of DM as a segmental progeroid disorder.

ZMPSTE24 missense mutations that cause progeroid diseases decrease prelamin A cleavage activity and/or protein stability

The human zinc metalloprotease ZMPSTE24 is an integral membrane protein crucial for the final step in the biogenesis of the nuclear scaffold protein lamin A, encoded by LMNA. After farnesylation and carboxyl methylation of its C-terminal CAAX motif, the lamin A precursor (prelamin A) undergoes proteolytic removal of its modified C-terminal 15 amino acids by ZMPSTE24. Mutations in LMNA or ZMPSTE24 that impede this prelamin A cleavage step cause the premature aging disease Hutchinson-Gilford progeria syndrome (HGPS), and the related progeroid disorders mandibuloacral dysplasia type B (MAD-B) and restrictive dermopathy (RD). Here, we report the development of a ‘humanized yeast system’ to assay ZMPSTE24-dependent cleavage of prelamin A and examine the eight known disease-associated ZMPSTE24 missense mutations. All mutations show diminished prelamin A processing and fall into three classes, with defects in activity, protein stability or both. Notably, some ZMPSTE24 mutants can be rescued by deleting the E3 ubiquitin ligase Doa10, involved in endoplasmic reticulum (ER)-associated degradation of misfolded membrane proteins, or by treatment with the proteasome inhibitor bortezomib. This finding may have important therapeutic implications for some patients. We also show that ZMPSTE24-mediated prelamin A cleavage can be uncoupled from the recently discovered role of ZMPSTE24 in clearance of ER membrane translocon-clogged substrates. Together with the crystal structure of ZMPSTE24, this humanized yeast system can guide structure-function studies to uncover mechanisms of prelamin A cleavage, translocon unclogging, and membrane protein folding and stability.

Summary: The zinc metalloprotease ZMPSTE24 performs the final step of prelamin A processing. Here, a yeast-based system shows differences in protein stability and activity for alleles of ZMPSTE24 that cause progeria disease.

Massive parallel sequencing identifies RAPSN and PDHA1 mutations causing fetal akinesia deformation sequence

INTRODUCTION

Fetal akinesia deformation sequence (FADS) or arthrogryposis multiplex congenita (AMC) is characterized by clinical ambiguity and genetic heterogeneity, hampering genetic diagnosis via traditional sequencing methods. Next generation sequencing (NGS) of all known disease-causing genes offers an elegant solution to identify the genetic etiology of AMC/FADS in a diagnostic setting.

METHODS

An in-house developed disease-associated gene panel was conducted in two unrelated fetuses with FADS. First, a de novo analysis was performed on the entire disease-associated gene panel. If no pathogenic mutation was identified, analysis of variants retained in a specific subpanel with arthrogryposis/fetal akinesia-causing genes was performed.

RESULTS

In the first family, FADS relates to a homozygous c.484G > A (p.Glu162Lys) mutation in the gene RAPSN. The second case concerns a sporadic patient with brain anomalies and arthrogryposis due to a de novo hemizygous c.498C > T splice-site mutation in the pyruvate dehydrogenase-alpha 1 (PDHA1) gene.

DISCUSSION

NGS facilitated genetic diagnosis, and hence genetic counseling, for both families with AMC/FADS. Biallelic RAPSN mutations typically result in congenital myasthenia syndrome, or occasionally in FADS. This is the first report attributing the RAPSN mutation c.484G > A, identified in a homozygous state in patient 1, to FADS. The second patient represents the first case of AMC due to a PDHA1 mutation, advocating that pyruvate dehydrogenase deficiency should be considered in the differential diagnosis of fetal akinesia. This study illustrates the relevance of a disease-associated-gene panel as a diagnostic tool in pregnancies complicated by this genetically heterogeneous condition.

Frame shift mutations of the ZMPSTE24 gene in two siblings with restrictive dermopathy

Restrictive dermopathy (RD) is a rare lethal autosomal recessive genodermatosis, characterized by abnormally rigid skin with prominent superficial vasculature, erosions and epidermal hyperkeratosis, dysplastic clavicles, joint contractures, mouth fixed in the 'O' position, small pinched nose, and neonatal death. Mutations of ZMPSTE24 and LMNA genes are reported as the causes of RD, with those of ZMPSTE24 being more prevalent. Here, we report on a familial c.50delA (p.Lys17Serfs*21) mutation of the ZMPSTE24 gene, causing RD in two siblings.

Diseases of the Nucleoskeleton

The nucleus is separated from the cytosol by the nuclear envelope, which is a double lipid bilayer composed of the outer nuclear membrane and the inner nuclear membrane. The intermediate filament proteins lamin A, lamin B, and lamin C form a network underlying the inner nuclear membrane. This proteinaceous network provides the nucleus with its strength, rigidity, and elasticity. Positioned within the inner nuclear membrane are more than 150 inner nuclear membrane proteins, many of which interact directly with lamins and require lamins for their inner nuclear membrane localization. Inner nuclear membrane proteins and the nuclear lamins define the nuclear lamina. These inner nuclear membrane proteins have tissue-specific expression and diverse functions including regulating cytoskeletal organization, nuclear architecture, cell cycle dynamics, and genomic organization. Loss or mutations in lamins and inner nuclear membrane proteins cause a wide spectrum of diseases. Here, I will review the functions of the well-studied nuclear lamina proteins and the diseases associated with loss or mutations in these proteins. © 2016 American Physiological Society. Compr Physiol 6:1655-1674, 2016.

Skin Disease in Laminopathy-Associated Premature Aging

The nuclear lamina, a protein network located under the nuclear membrane, has during the past decade found increasing interest due to its significant involvement in a range of genetic diseases, including the segmental premature aging syndromes Hutchinson-Gilford progeria syndrome, restrictive dermopathy, and atypical Werner syndrome. In this review we examine these diseases, some caused by mutations in the LMNA gene, and their skin disease features. Advances within this area might also provide novel insights into the biology of skin aging, as recent data suggest that low levels of progerin are expressed in unaffected individuals and these levels increase with aging.

New ZMPSTE24 (FACE1) mutations in patients affected with restrictive dermopathy or related progeroid syndromes and mutation update

Restrictive dermopathy (RD) is a rare and extremely severe congenital genodermatosis, characterized by a tight rigid skin with erosions at flexure sites, multiple joint contractures, low bone density and pulmonary insufficiency generally leading to death in the perinatal period. RD is caused in most patients by compound heterozygous or homozygous ZMPSTE24 null mutations. This gene encodes a metalloprotease specifically involved in lamin A post-translational processing. Here, we report a total of 16 families for whom diagnosis and molecular defects were clearly established. Among them, we report seven new ZMPSTE24 mutations, identified in classical RD or Mandibulo-acral dysplasia (MAD) affected patients. We also report nine families with one or two affected children carrying the common, homozygous thymine insertion in exon 9 and demonstrate the lack of a founder effect. In addition, we describe several new ZMPSTE24 variants identified in unaffected controls or in patients affected with non-classical progeroid syndromes. In addition, this mutation update includes a comprehensive search of the literature on previously described ZMPSTE24 mutations and associated phenotypes. Our comprehensive analysis of the molecular pathology supported the general rule: complete loss-of-function of ZMPSTE24 leads to RD, whereas other less severe phenotypes are associated with at least one haploinsufficient allele.

Embryonic expression of the common progeroid lamin A splice mutation arrests postnatal skin development

Hutchinson-Gilford progeria syndrome (HGPS) and restrictive dermopathy (RD) are two laminopathies caused by mutations leading to cellular accumulation of prelamin A or one of its truncated forms, progerin. One proposed mechanism for the more severe symptoms in patients with RD compared with HGPS is that higher levels of farnesylated lamin A are produced in RD. Here, we show evidence in support of that hypothesis. Overexpression of the most common progeroid lamin A mutation (LMNA c.1824C>T, p.G608G) during skin development results in a severe phenotype, characterized by dry scaly skin. At postnatal day 5 (PD5), progeroid animals showed a hyperplastic epidermis, disorganized sebaceous glands and an acute inflammatory dermal response, also involving the hypodermal fat layer. PD5 animals also showed an upregulation of multiple inflammatory response genes and an activated NF-kB target pathway. Careful analysis of the interfollicular epidermis showed aberrant expression of the lamin B receptor (LBR) in the suprabasal layer. Prolonged expression of LBR, in 14.06% of the cells, likely contributes to the observed arrest of skin development, clearly evident at PD4 when the skin had developed into single-layer epithelium in the wild-type animals while progeroid animals still had the multilayered appearance typical for skin at PD3. Suprabasal cells expressing LBR showed altered DNA distribution, suggesting the induction of gene expression changes. Despite the formation of a functional epidermal barrier and proven functionality of the gap junctions, progeroid animals displayed a greater rate of water loss as compared with wild-type littermates and died within the first two postnatal weeks.

Arthrogryposis and fetal hypomobility syndrome

Arthrogryposis is a heterogeneous condition, evident from birth, which can be defined as multiple contractures of the joints. The etiology is multifold: genetic disorders of the central or peripheral nervous system, or of the connective tissue leading to decreased fetal movements, and vascular and environmental causes. The problem begins in utero. There may be overlapping conditions between sporadic, syndromic, neurogenic, myopathic and metabolic types. The workup should include a family tree. Systemic involvement, for example of the renal and pulmonary systems, may be encountered in associated syndromes. Motor neuron disorders leading to the condition are the most commonly seen type. Fetal or neonatal akinesia/hypokinesia is at the severe end of the spectrum, in which there is literally intrauterine limitation of movement. Children with amyplasia are born with little or diminished muscle bulk of the extremities. Distal arthrogryposis is almost always a dominantly inherited condition. A multidisciplinary care approach is required in order to provide optimum healthcare. The management team should include a nutritionist and a physiotherapist. Genetic counseling is possible in most instances. A truly genetic cause can be identified in more than 50% of cases. Survivors, though handicapped, can lead near normal lives.

Intrauterine growth restriction and genetic determinants - existing findings, problems, and further direction

Fetal growth is determined largely by the nutrient supply, placental transport function, and growth hormones. Recently, gene mutation and expression, especially of those genes associated with the proteins that are related to the fetal growth, have been reported to play an important role in the development of intrauterine growth restriction (IUGR). Fetal growth epigenetics, a new concept in fetal growth, has resulted from studies on fetal programing. This paper outlines the findings of our serial studies on IUGR, and summarizes data on IUGR animal models, placental function in transferring nutrients, cell proliferation dynamics in IUGR, and experimental treatment of IUGR. We review genetic approaches to IUGR, especially those relating to growth factor genes, angiotensinogen genes and other gene mutations. We also discuss the epigenetics of fetal growth and future study directions on fetal growth restriction. These should be valuable in elucidating the mechanisms employed by the fetus and in helping to develop interventional strategies that might prevent the development of IUGR.

Human ZMPSTE24 disease mutations: residual proteolytic activity correlates with disease severity

The zinc metalloprotease ZMPSTE24 plays a critical role in nuclear lamin biology by cleaving the prenylated and carboxylmethylated 15-amino acid tail from the C-terminus of prelamin A to yield mature lamin A. A defect in this proteolytic event, caused by a mutation in the lamin A gene (LMNA) that eliminates the ZMPSTE24 cleavage site, underlies the premature aging disease Hutchinson-Gilford Progeria Syndrome (HGPS). Likewise, mutations in the ZMPSTE24 gene that result in decreased enzyme function cause a spectrum of diseases that share certain features of premature aging. Twenty human ZMPSTE24 alleles have been identified that are associated with three disease categories of increasing severity: mandibuloacral dysplasia type B (MAD-B), severe progeria (atypical 'HGPS') and restrictive dermopathy (RD). To determine whether a correlation exists between decreasing ZMPSTE24 protease activity and increasing disease severity, we expressed mutant alleles of ZMPSTE24 in yeast and optimized in vivo yeast mating assays to directly compare the activity of alleles associated with each disease category. We also measured the activity of yeast crude membranes containing the ZMPSTE24 mutant proteins in vitro. We determined that, in general, the residual activity of ZMPSTE24 patient alleles correlates with disease severity. Complete loss-of-function alleles are associated with RD, whereas retention of partial, measureable activity results in MAD-B or severe progeria. Importantly, our assays can discriminate small differences in activity among the mutants, confirming that the methods presented here will be useful for characterizing any new ZMPSTE24 mutations that are discovered.

Requirements for efficient proteolytic cleavage of prelamin A by ZMPSTE24

BACKGROUND

The proteolytic maturation of the nuclear protein lamin A by the zinc metalloprotease ZMPSTE24 is critical for human health. The lamin A precursor, prelamin A, undergoes a multi-step maturation process that includes CAAX processing (farnesylation, proteolysis and carboxylmethylation of the C-terminal CAAX motif), followed by ZMPSTE24-mediated cleavage of the last 15 amino acids, including the modified C-terminus. Failure to cleave the prelamin A "tail", due to mutations in either prelamin A or ZMPSTE24, results in a permanently prenylated form of prelamin A that underlies the premature aging disease Hutchinson-Gilford Progeria Syndrome (HGPS) and related progeroid disorders.

METHODOLOGY/PRINCIPAL FINDINGS

Here we have investigated the features of the prelamin A substrate that are required for efficient cleavage by ZMPSTE24. We find that the C-terminal 41 amino acids of prelamin A contain sufficient context to allow cleavage of the tail by ZMPSTE24. We have identified several mutations in amino acids immediately surrounding the cleavage site (between Y646 and L647) that interfere with efficient cleavage of the prelamin A tail; these mutations include R644C, L648A and N650A, in addition to the previously reported L647R. Our data suggests that 9 of the 15 residues within the cleaved tail that lie immediately upstream of the CAAX motif are not critical for ZMPSTE24-mediated cleavage, as they can be replaced by the 9 amino acid HA epitope. However, duplication of the same 9 amino acids (to increase the distance between the prenyl group and the cleavage site) impairs the ability of ZMPSTE24 to cleave prelamin A.

CONCLUSIONS/SIGNIFICANCE

Our data reveals amino acid preferences flanking the ZMPSTE24 cleavage site of prelamin A and suggests that spacing from the farnesyl-cysteine to the cleavage site is important for optimal ZMPSTE24 cleavage. These studies begin to elucidate the substrate requirements of an enzyme activity critical to human health and longevity.

Early onset mandibuloacral dysplasia due to compound heterozygous mutations in ZMPSTE24

Mandibuloacral dysplasia (MAD) is an autosomal recessive disorder characterized by hypoplasia of the mandible and clavicles, acro-osteolysis, and lipodystrophy due to mutations in LMNA or ZMPSTE24. Only six MAD patients are reported so far with ZMPSTE24 mutations and limited phenotypic data are available for them. Here, we report on two brothers (4 years and 9-month old) with early onset MAD due to ZMPSTE24 mutations in whom thin skin was noted as early as 5 months of age. Both had micrognathia, mottled hyperpigmentation, and enlarged fontanelles but little evidence of lipodystrophy. There was no delay of mental development. The older brother had small pinched nose, short clavicles, acro-osteolysis, stunted growth, joint stiffness, and repeated fractures. There was no evidence of renal disease. Both patients were compound heterozygotes harboring a previously reported missense ZMPSTE24 mutation, p.Pro248Leu, and a novel null mutation, p.Trp450stop. These patients and the review of literature reveal that compared to MAD patients with LMNA mutations, those with ZMPSTE24 mutations develop manifestations earlier in life. Other distinguishing features in MAD due to ZMPSTE24 mutations may include premature birth, renal disease, calcified skin nodules, and lack of acanthosis nigricans. We conclude that in patients with MAD due to ZMPSTE24 mutations, the onset of disease manifestations such as thin skin and micrognathia occurs as early as 5 months of age. In these patients, skeletal phenotype presents earlier whereas lipodystrophy and renal disease may occur later in life.

Type B mandibuloacral dysplasia with congenital myopathy due to homozygous ZMPSTE24 missense mutation

Mutation in ZMPSTE24 gene, encoding a major metalloprotease, leads to defective prelamin A processing and causes type B mandibuloacral dysplasia, as well as the lethal neonatal restrictive dermopathy syndrome. Phenotype severity is correlated with the residual enzyme activity of ZMPSTE24 and accumulation of prelamin A. We had previously demonstrated that a complete loss of function in ZMPSTE24 was lethal in the neonatal period, whereas compound heterozygous mutations including one PTC and one missense mutation were associated with type B mandibuloacral dysplasia. In this study, we report a 30-year longitudinal clinical survey of a patient harboring a novel severe and complex phenotype, combining an early-onset progeroid syndrome and a congenital myopathy with fiber-type disproportion. A unique homozygous missense ZMPSTE24 mutation (c.281T>C, p.Leu94Pro) was identified and predicted to produce two possible ZMPSTE24 conformations, leading to a partial loss of function. Western blot analysis revealed a major reduction of ZMPSTE24, together with the presence of unprocessed prelamin A and decreased levels of lamin A, in the patient's primary skin fibroblasts. These cells exhibited significant reductions in lifespan associated with major abnormalities of the nuclear shape and structure. This is the first report of MAD presenting with confirmed myopathic abnormalities associated with ZMPSTE24 defects, extending the clinical spectrum of ZMPSTE24 gene mutations. Moreover, our results suggest that defective prelamin A processing affects muscle regeneration and development, thus providing new insights into the disease mechanism of prelamin A-defective associated syndromes in general.

Homozygous null mutations in ZMPSTE24 in restrictive dermopathy: evidence of genetic heterogeneity

Restrictive dermopathy (RD) results in stillbirth or early neonatal death. RD is characterized by prematurity, intrauterine growth retardation, fixed facial expression, micrognathia, mouth in the 'o' position, rigid and tense skin with erosions and denudations and multiple joint contractures. Nearly all 25 previously reported neonates with RD had homozygous or compound heterozygous null mutations in the ZMPSTE24 gene. Here, we report three new cases of RD; all died within 3 weeks of birth. One of them had a previously reported homozygous c.1085dupT (p.Leu362PhefsX19) mutation, the second case had a novel homozygous c.1020G>A (p.Trp340X) null mutation in ZMPSTE24, but the third case, a stillborn with features of RD except for the presence of tapering rather than rounded, bulbous digits, harbored no disease-causing mutations in LMNA or ZMPSTE24. In the newborn with a novel ZMPSTE24 mutation, unique features included butterfly-shaped thoracic 5 vertebra and the bulbous appearance of the distal clavicles. Skin biopsies from both the stillborn fetus and the newborn with c.1020G>A ZMPSTE24 mutation showed absence of elastic fibers throughout the dermis. This report provides evidence of genetic heterogeneity among RD and concludes that there may be an additional locus for RD which remains to be identified.