Marfan syndrome as a paradigm for transcript-targeted preimplantation diagnosis of heterozygous mutations

Fibrillin microfibrils and proteases, key integrators of fibrotic pathways

Supramolecular networks composed of multi-domain ECM proteins represent intricate cellular microenvironments which are required to balance tissue homeostasis and direct remodeling. Structural deficiency in ECM proteins results in imbalances in ECM-cell communication resulting often times in fibrotic reactions. To understand how individual components of the ECM integrate communication with the cell surface by presenting growth factors or providing fine-tuned biomechanical properties is mandatory for gaining a better understanding of disease mechanisms in the quest for new therapeutic approaches. Here we provide an overview about what we can learn from inherited connective tissue disorders caused primarily by mutations in fibrillin-1 and binding partners as well as by altered ECM processing leading to defined structural changes and similar functional knock-in mouse models. We will utilize this knowledge to propose new molecular hypotheses which should be tested in future studies.

Pregnancy and Marfan syndrome

Pregnancy in women with Marfan syndrome (MFS) presents challenges to the clinician and the patient due to the increased incidence of maternal complications and involvement of the fetus, and deserves special consideration. The leading cause of morbidity and mortality in MFS is aortic dissection. This article presents an extensive review of available clinical information and provides recommendations for the management of patients with MFS during pregnancy.

De Novo Paternal FBN1 Mutation Detected in Embryos Before Implantation

Background

Marfan syndrome (MFS) is an autosomal dominant disease caused by mutations in the Fibrillin (FBN)1 gene and characterized by disorders in the cardiovascular, skeletal, and visual systems. The diversity of mutations and phenotypic heterogeneity of MFS make prenatal molecular diagnoses difficult. In this study, we used pre-implantation genetic diagnosis (PGD) to identify the pathogenic mutation in a male patient with MFS and to determine whether his offspring would be free of the disease.

Material/Methods

The history and pedigree of the proband were analyzed. Mutation analysis was performed on the couple and immediate family members. The couple chose IVF treatment and 4 blastocysts were biopsied. PGD was carried out by targeted high-throughput sequencing of the FBN1 gene in the embryos, along with single-nucleotide polymorphism haplotyping. Sanger sequencing was used to confirm the causative mutation.

Results

c.2647T>C (p.Trp883Arg) was identified as the de novo likely pathogenic mutation in the proband. Whole-genome amplification and sequencing of the 3 embryos revealed that they did not carry the mutation, and 1 blastocyst was transferred back to the uterus. The amniocentesis test result analyzed by Sanger sequencing confirmed the PGD. A premature but healthy infant free of heart malformations was born.

Conclusions

The de novo mutation c.2647T>C (p.Trp883Arg) in FBN1 was identified in a Chinese patient with MFS. Embryos without the mutation were identified by PGD and resulted in a successful pregnancy.

Pregnancy in Marfan syndrome: maternal and fetal risk and recommendations for patient assessment and management

Pregnancy in women with the Marfan syndrome (MFS) is associated with the potential for a catastrophic and even fatal acute aortic dissection and the risk of having a child who will inherit the syndrome. The approach to pregnancy in patients with MFS is therefore challenging and deserves special considerations. This article presents an extensive review of available clinical information and provides recommendations for the management of patients with MFS during pregnancy.

Diagnosis and management of Marfan syndrome

Marfan syndrome is a disorder of the connective tissue that is inherited in an autosomal-dominant fashion and is caused by mutations in the gene coding for fibrillin-1, FBN1. Although complications of the syndrome may involve the eye, the lung and the skeleton, the high mortality of untreated cases results almost exclusively from cardiovascular complications, including aortic dissection and rupture. Recently, a series of experiments has begun to elucidate the complex molecular etiology of Marfan syndrome, and a number of new heritable syndromes with an associated risk for aortic complications, such as Loeys–Dietz syndrome types I and II, have been described. The multiorgan involvement of many of these syndromes requires multidisciplinary expert centers that can increase the average life expectancy of affected patients from only 32 years to over 60 years. The present article both reviews classical standards of managing cardiovascular manifestations and outlines significant advances in recent research with focus on their impact on future diagnostic and therapeutic options.

Preimplantation genetic diagnosis of Marfan syndrome using multiple displacement amplification

OBJECTIVE

To evaluate the use of multiple displacement amplification (MDA) for whole-genome amplification in the preimplantation genetic diagnosis (PGD) of Marfan syndrome.

DESIGN

Multiple displacement amplification was used to amplify the whole-genome directly from a single cell. The MDA product was used for polymerase chain reaction (PCR) analysis of five different loci. At this point MDA was used to develop a PGD-Marfan syndrome program.

SETTING

Fertility and gynecology private center in Alicante, Spain.

PATIENT(S)

A couple in which the husband is affected by Marfan syndrome and carries a novel mutation in the FBN-1 gene.

INTERVENTION(S)

The MDA of single cells and PCR tests for PGD.

MAIN OUTCOME MEASURE(S)

Allele drop-out (ADO), amplification efficiency rates, and the ability to detect Marfan syndrome using MDA.

RESULT(S)

We report that isothermal whole-genome amplification from single cells allowed analysis of five different loci using standard conditions. The development of a MDA-PGD protocol for Marfan syndrome allowed for the diagnosis of seven embryos. These were biopsied on day 3 of culture and analyzed. Two healthy embryos were transferred 48 hours after culture, resulting in a singleton ongoing pregnancy and the birth of a healthy child.

CONCLUSION(S)

The MDA technique is useful for overcoming the problem of insufficient genomic DNA in PGD. The use of MDA as a universal step marks a new cycle for PGD as it allows for the diagnosis of any known gene defect by standard methods and conditions.

Preimplantation genetic diagnosis for Marfan syndrome

OBJECTIVE

To develop and apply efficient and reliable protocols for preimplantation genetic diagnosis (PGD) for Marfan syndrome.

DESIGN

Two mutation-specific protocols were developed, and the markers D15S1028, D15S992, D15S196, D15S576, D15S123, and D15S143 were used to set up four multiplex polymerase chain reactions (PCRs).

SETTING

Research Center Reproduction and Genetics.

PATIENT(S)

Ten couples carrying mutations in the FBN1 gene.

INTERVENTION(S)

Six PGD protocols were developed for 10 couples, and 7 of them underwent a total of 16 clinical cycles.

MAIN OUTCOME MEASURE(S)

Amplification, allele drop-out (ADO), and contamination rates during the preclinical assays. DNA analyses of blastomeres from embryos biopsied during PGD cycles.

RESULT(S)

Six different protocols were set up, with the main objective being to to use one protocol for several couples. A total of 16 PGD cycles were performed, which resulted in the delivery of an unaffected boy and three ongoing pregnancies.

CONCLUSION(S)

The development of single-cell multiplex PCRs for linked markers and its use in PGD reduce the workload of the genetic diagnostic laboratory as well as the average waiting time for patients. This approach also allows for the simultaneous and accurate detection of recombination, contamination, and ADO, thereby increasing the reliability of the diagnosis.

Association of abnormal morphology and altered gene expression in human preimplantation embryos

OBJECTIVE

We set out to characterize the expression of nine genes in human preimplantation embryos and determine whether abnormal morphology is associated with altered gene activity.

DESIGN

Reverse transcription and real-time polymerase chain reaction were used to quantify the expression of multiple genes in each embryo. The genes studied have various important cellular roles (e.g., cell cycle regulation, DNA repair, and apoptosis).

SETTING

Research laboratory working closely with a clinical IVF practice.

PATIENT(S)

Over 50 embryos were donated by infertile patients (various etiologies). Among these, all major stages of preimplantation development and a variety of common morphologic abnormalities were represented.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Quantification of mRNA transcripts.

RESULT(S)

We detected an association between certain forms of abnormal morphology and disturbances of gene activity. Cellular fragmentation was associated with altered expression of several genes, including TP53, suggesting that fragmenting blastomeres are suffering stress of a type monitored by p53, possibly as a consequence of suboptimal culture conditions.

CONCLUSION(S)

Appropriate gene expression is vital for the regulation of metabolic pathways and key developmental events. Our data indicates a possible causal relationship between changes in gene expression and the formation of clinically relevant abnormal embryo morphologies. We hypothesize that embryos with expression profiles characteristic of good morphology and appropriate for their developmental stage have the greatest potential for implantation. If confirmed, this could lead to a new generation of preimplantation genetic diagnosis (PGD) tests for assessing embryo viability and predicting implantation potential.

Marfan's syndrome

Marfan's syndrome is a systemic disorder of connective tissue caused by mutations in the extracellular matrix protein fibrillin 1. Cardinal manifestations include proximal aortic aneurysm, dislocation of the ocular lens, and long-bone overgrowth. Important advances have been made in the diagnosis and medical and surgical care of affected individuals, yet substantial morbidity and premature mortality remain associated with this disorder. Progress has been made with genetically defined mouse models to elucidate the pathogenetic sequence that is initiated by fibrillin-1 deficiency. The new understanding is that many aspects of the disease are caused by altered regulation of transforming growth factor beta (TGFbeta), a family of cytokines that affect cellular performance, highlighting the potential therapeutic application of TGFbeta antagonists. Insights derived from studying this mendelian disorder are anticipated to have relevance for more common and non-syndromic presentations of selected aspects of the Marfan phenotype.

Sentinel lymph node mapping and molecular staging in nonsmall cell lung carcinoma

BACKGROUND

Lymph node (LN) involvement predicts recurrence in patients who have undergone resection of apparently localized nonsmall cell lung carcinoma (NSCLC). Standard detection methods for LN disease have a low sensitivity, and many patients with apparent N0 disease status develop recurrent disease. Molecular techniques can improve the detection of micrometastases, whereas sentinel lymph node (SLN) mapping can indicate which LN may contain micrometastases. These methods, although potentially complementary, have not, to the authors' knowledge, been used together previously.

METHODS

The authors used SLN mapping and molecular staging to improve the detection of LN micrometastases in patients with NSCLC. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis for cytokeratin-7 (CK7), expressed both in normal lung and in malignant lung, was used to identify tumor-derived material in LN.

RESULTS

SLN mapping was performed in 13 patients, with 1-3 SLNs identified in each patient, and sufficient RNA for RT-PCR was obtained in 12 of these 13 patients. Eleven of 12 tumors expressed CK7. Overall, 32 LNs were positive for CK7, including 13 of 21 SLNs. Ten of 11 patients with evaluable SLNs had at least 1 CK7-positive SLN. Routine pathology showed Stage I disease in eight patients, T3N0 disease in one patient, and LN-positive disease in two patients. Of the nine patients with N0 disease according to routine pathology that was evaluable by RT-PCR, eight patients were upstaged by this technique. All patients with positive LN status by routine pathology who were evaluable by RT-PCR analysis had positive RT-PCR results.

CONCLUSIONS

LN micrometastases were common in resected NSCLC, including patients with N0 disease according to routine pathology. SLN mapping was useful for identifying disease-containing LNs. This approach may be useful for stratifying histologically N0 patients into higher risk and lower risk groups.

Expression of genes regulating chromosome segregation, the cell cycle and apoptosis during human preimplantation development

BACKGROUND

Appropriate gene expression is vital for the regulation of developmental processes. Despite this fact there is a remarkable paucity of information concerning gene activity during preimplantation development.

METHODS

We employed reverse transcription and real-time fluorescent PCR to quantify the expression of nine genes (BRCA1, BRCA2, ATM, TP53, RB1, MAD2, BUB1, APC and beta-actin) in oocytes and embryos. A full characterization of all genes was achieved in 42 embryos and four oocytes. The genes analysed have a variety of important cellular functions.

RESULTS

Oocytes displayed relatively high levels of mRNA transcripts, while 2-3-cell embryos were seen to contain very little mRNA from any of the genes examined. Recovery of expression levels was not seen until the 4-cell stage or later, with the presumptive activation of the embryonic genome. Some genes displayed sharp increases in expression in embryos composed of 4-8 cells, but, for most, maximum expression was not achieved until the blastocyst stage.

CONCLUSIONS

Our data show that it is possible to define characteristic gene expression profiles for each stage of human preimplantation development. The identification of genes active at defined preimplantation phases may provide clues to the cellular pathways utilized at specific stages of development. Expression of genes that function in DNA repair pathways indicate that DNA damage may be common at the cleavage stage. We suggest that specific patterns of gene expression may be indicative of embryo implantation potential.

The Marfan syndrome

The Marfan syndrome (MFS), initially described just over 100 years ago, was among the first conditions classified as a heritable disorder of connective tissue. MFS lies at one end of a phenotypic continuum, with people in the general population who have one or another of the features of MFS at the other end, and those with a variety of other conditions in between. Diagnosis of MFS and these other conditions remains based on clinical features. Mutations in FBN1, the gene that encodes fibrillin-1, are responsible for MFS and (in a few patients) other disorders in the continuum. In addition to skeletal, ocular, and cardiovascular features, patients with MFS have involvement of the skin, integument, lungs, and muscle tissue. Over the past 30 years, evolution of aggressive medical and surgical management of the cardiovascular problems, especially mitral valve prolapse, aortic dilatation, and aortic dissection, has resulted in considerable improvement in life expectancy.

Synthesis of elastic microfibrillar components fibrillin-1 and fibrillin-2 by human optic nerve head astrocytes in situ and in vitro

The purpose of this study was to identify elastic microfibrillar components fibrillin-1 and fibrillin-2 in optic nerve heads of adult normal and glaucomatous subjects, in cultured optic nerve head astrocytes (type 1B astrocytes), as well as fibrillin-1 in fetal optic nerve heads. To characterize synthesis and gene expression of microfibrillar proteins in human optic nerve heads and cultured type 1B astrocytes, light microscopy immunohistochemistry, in situ hybridization, and RT-PCR or Northern blots were performed. Our results demonstrated that fibrillin-1 was associated with blood vessels, astrocytes in the glial columns and cribriform plates, and with astrocyte processes in the nerve bundles in all samples. In glaucomatous optic nerves there was enhanced fibrillin-1 immunoreactivity, especially surrounding blood vessels. Fibrillin-2 was localized primarily to blood vessels in all samples, without qualitative differences between normal and glaucomatous samples. In fetal optic nerve heads fibrillin-1 mRNA was localized to glial cells and to the blood vessel walls. In adult optic nerve heads, there was little fibrillin-1 mRNA as detectable by in situ hybridization and RT-PCR. There was no detectable upregulation of fibrillin-1 mRNA in glaucoma. In cultured type 1B astrocytes, fibrillin-1 staining was mostly pericellular. There was little fibrillin-2 immunoreactivity. In conclusion, astrocytes from the optic nerve head deposit elastic microfibrillar components in situ and in vitro, with a predominance of fibrillin-1. Upregulation of fibrillin-1 mRNA was not observed in glaucoma, suggesting that increased transcription may occur early in the disease process. Cultures of type 1B astrocytes from the optic nerve head provides a useful model to study mechanisms regulating the interactions of elastin and the microfibrils in optic nerve head astrocytes.

Recycling of a single human blastomere fixed on a microscopic slide for sexing and diagnosis of specific mutations by various types of polymerase chain reaction

OBJECTIVE

To investigate the suitability of recycling single blastomeres to assess multiple genetic variables for preimplantation genetic diagnosis.

DESIGN

Prospective randomized study.

SETTING

An academic medical center.

PATIENT(S)

Patients undergoing IVF-ET.

INTERVENTION(S)

Blastomeres were disaggregated from donated embryos obtained from patients.

MAIN OUTCOME MEASURE(S)

Polymerase chain reaction (PCR) amplification products.

RESULT(S)

Fifty-eight blastomeres individually fixed on slides were separated into four groups. Sequential PCRs (group I, n = 30), primed in situ labeling (PRINS) before five sequential PCRs (group II, n = 10), staining with hematoxylin before performing five sequential PCRs (group III, n = 11) and preamplification of whole DNAs by degenerate oligonucleotide primer (DOP) before performing PCR were executed. The amplification efficiencies of five sequential PCRs were 100%, 100%, 96.6%, 83.3%, 56.7% for group I; 100% 100%, 100%, 80%, 40% for group II; 54.5%, 36.4%, 18.2%, 9.1% for group III; and 100%, 100%, 100%, 100%, 100% for group IV.

CONCLUSION(S)

Blastomeres fixed for PRINS can be recycled for PCR to obtain more genetic information. Hematoxylin staining appears to increase the incidence of failed amplification. Preamplification of whole genomic DNAs by DOP-PCR appears to facilitate diagnosis with high efficiency.

Preimplantation genetic diagnosis of Marfan syndrome with the use of fluorescent polymerase chain reaction and the Automated Laser Fluorescence DNA Sequencer

OBJECTIVE

To develop and apply clinical preimplantation genetic diagnosis (PGD) for Marfan syndrome.

DESIGN

Case report.

SETTING

Centers for medical genetics and reproductive medicine in university hospitals.

PATIENT(S)

One couple in which the husband was affected with Marfan syndrome.

INTERVENTION(S)

The couple underwent three intracytoplasmic sperm injection cycles.

MAIN OUTCOME MEASURE(S)

The correct diagnosis was obtained for embryos in three PGD cycles.

RESULT(S)

Although all the PGD cycles were followed by ET, no pregnancy ensued.

CONCLUSION(S)

This assay can provide a reliable and accurate preimplantation diagnosis of Marfan syndrome.

Preimplantation genetic diagnosis of human embryos for Marfan's syndrome

PURPOSE

Single-cell nested polymerase chain reaction (PCR) and Ddel endonuclease digestion were used to detect the presence of a Marfan's syndrome mutation in human preimplantation embryos derived from in vitro fertilization (IVF). These procedures were conducted to eliminate the possibility of transmission of the affected allele from the father to his offspring. The mutation on chromosome 15 is transmitted as an autosomal dominant trait, and the chance of having a child affected with the disease is 50%.

METHODS

A couple presented to the Program for In Vitro Fertilization, Reproductive Surgery and Infertility for preimplantation genetic diagnosis. IVF was performed and embryo biopsy was done on day 3 embryos. Single blastomeres were removed from embryos and subjected to nested PCR analysis and endonuclease digestion to detect a Marfan's syndrome mutation located on chromosome 15 inherited from the father.

RESULTS

Thirteen oocytes were injected with spermatozoa using intracytoplasmic sperm injection, and nine fertilized normally. Following embryo biopsy and polymerase chain reaction amplification-Ddel endonuclease digestion, five embryos were detected that were positive for the mutation. The four non-affected embryos were transferred to the uterus, resulting in a healthy and normal ongoing pregnancy.

Preimplantation genetic diagnosis of severe inherited skin diseases

Considerable progress has been made recently in elucidating the molecular pathology underlying several forms of inherited skin diseases. One of the most immediate benefits of these discoveries has been the development of DNA-based prenatal diagnosis in pregnancies at risk for recurrence of a particular disorder. In less than 2 decades, prenatal testing has progressed from mid-trimester fetal skin biopsies or protein analysis in a limited number of conditions to first trimester chorionic villus sampling in a much broader range of genodermatoses. Advances in in vitro fertilization protocols and embryo manipulation technology have further led to the feasibility of even earlier prenatal diagnosis through preimplantation genetic diagnosis. This article details some of the recent advances in genetic skin disease research relevant to prenatal diagnosis and explores the possibilities and practicalities of preimplantation genetic diagnosis in the prevention of these conditions.

Scientific and ethical issues of preimplantation diagnosis

Preimplantation diagnosis (PID) offers couples at high risk of having offspring affected with a genetic disorder the possibility of an early prenatal diagnosis. For many couples this approach will give the opportunity to avoid a selective termination of affected pregnancies. Substantial advances were made in PID since the report, in 1990, of the first birth obtained after PID. Yet, many technical hazards have to be solved for PID to become a standard clinical tool. The very close correlation existing between the forthcoming developments in the fields of PID and human genome mapping will improve the reliability and efficiency of genetic diagnosis. In the near future, the procedure may also become easier and safer. As a consequence, the indications for PID could be extended to other genetic defects, such as multifactorial diseases. They could also be extended to cases with no medical background, such as social gender selection or behavioural traits. In this perspective, it is now time for both the medical and scientific communities to identify the ethical issues related to these potential new indications.

Paternal transcripts for glucose-6-phosphate dehydrogenase and adenosine deaminase are first detectable in the human preimplantation embryo at the three- to four-cell stage

The transition between dependence on maternal transcripts and proteins inherited in the oocyte and embryonic gene expression in the human preimplantation embryo occurs at the four- to eight-cell stage. Recently, studies using reverse transcriptase polymerase chain reaction (RT-PCR) have detected paternal transcripts for the Y-linked genes, ZFY and SRY, and the myotonic dystrophy associated protein kinase gene, DK, as early as the late pronucleate one-cell stage. However, expression at the protein level has not been demonstrated and its function at these early stages is unknown. Using coding sequence polymorphisms to distinguish maternal and paternal transcripts, we have examined the transcription of two ubiquitously expressed genes: X-linked glucose-6-phosphate dehydrogenase (G6PD) and adenosine deaminase (ADA). Both G6PD and ADA are housekeeping genes with TATA-less promoters which, because of their roles in metabolism and ubiquitous expression, may provide a more reliable indication of the timing of activation of the embryonic genome. They also each have biallelic polymorphisms with a high heterozygosity ratio which can be detected by restriction digestion. Couples undergoing in vitro fertilization (IVF) were screened for these polymorphisms. Individual spare oocytes and embryos at different stages of preimplantation development were analyzed by RT-PCR and appropriate restriction digestion in those cases in which the male partner carried a different allele to the female partner. In addition, since only female embryos inherit the paternal allele of X-linked G6PD, cDNA was also analyzed for ZFX/ZFY transcripts to identify the sex of each embryo. One hundred and twenty three individual oocytes and embryos were analyzed by RT-PCR and restriction digestion to detect the paternal transcripts from the polymorphic alleles. Maternal transcripts for G6PD, ADA, and ZFX were detected in all oocytes and embryos and at all stages. Following restriction digestion, paternal G6PD and ZFY transcripts were first detected at the four-cell stage and paternal ADA transcripts in an embryo at the three-cell stage coinciding with the onset of dependency on transcription from the embryonic genome. This approach should be widely applicable to other genes since similar polymorphisms exist in the coding regions of many genes.

Update in preimplantation genetic diagnosis. Age, genetics, and infertility

PGD has been successfully used for several years. Over 40 babies have been born worldwide by use of these techniques. Unfortunately, a number of misdiagnoses have been made, a distressing consequence of a new frontier. Significant advances have been made to improve the efficiency and accuracy of PCR and FISH. The widespread use of this technology awaits further documentation of safety and accuracy. Other issues must also be addressed. First, the cost-effectiveness of the techniques relative to the traditional alternatives must be evaluated. A number of ethical issues regarding embryo screening must be addressed including what diseases are serious enough to warrant the procedure. Another concern is the use of this technology for nongenetic disorders such as gender selection. Finally, the experimental nature of these procedures must continually be discussed with patients, and long-term follow-up studies must be undertaken. Development of more accurate and less expensive assays coupled with improved IVF success rates may make PGD a more widely used clinical tool. The future awaits these developments.

Preimplantation genetic diagnosis: strategies and surprises

Several inherited diseases can now be diagnosed by genetic analysis of single cells biopsied from human eggs and preimplantation embryos following in vitro fertilization (IVF). 'At risk' couples can, therefore, have only unaffected embryos replaced in the uterus and avoid the possibility of terminating a pregnancy that might only be diagnosed as affected later is gestation. Single-cell genetic analysis has also provided powerful tools for studying genetic defects arising during early human development. Recent studies of cleavage-stage human embryos have revealed an unexpectedly high incidence of postzygotic chromosomal abnormalities, which might arise because of a lack of cell-cycle checkpoints before the embryonic genome is activated. These genetic abnormalities are likely to contribute to early pregnancy loss and have important implications for improving pregnancy rates in infertile couples by assisted reproduction.

Fibrillln mutations in Marfan syndrome and related phenotypes

A casual association has been established between mutations in the fibrillin 1 gene and Marfan syndrome and related phenotypes. Analysis of mutations in these disease types has provided new insights into microfibril assembly and function. These include evidence for a mutation in a fibrillin 1 domain associated with severe phenotype; indication of profibrillin processing by a furin-like endoprotease; linkage between extracellular processing and fibrillin 1 polymerization; and involvement of calcium binding in monomer stabilization and microfibril assembly. Identification of intragenic DNA polymorphisms and determination of intron/exon junction sequences have significantly improved our ability to diagnose Marfan syndrome and to detect fibrillin 1 mutations. Additional work has provided strong evidence for structural and functional heterogeneity of microfibrillin. The evidence includes the identification of fibrillin 2, a microfibrillar component structurally related to fibrillin 1; the differential pattern of gene expression of the two fibrillin; and the association of fibrillin 2 mutations with congenital contractural arachnodactyly.

A tandem duplication within the fibrillin 1 gene is associated with the mouse tight skin mutation

Mice carrying the Tight skin (Tsk) mutation have thickened skin and visceral fibrosis resulting from an accumulation of extracellular matrix molecules. These and other connective tissue abnormalities have made Tskl + mice models for scleroderma, hereditary emphysema, and myocardial hypertrophy. Previously we localized Tsk to mouse chromosome 2 in a region syntenic with human chromosome 15. The microfibrillar glycoprotein gene, fibrillin 1 (FBN1), on human chromosome 15q, provided a candidate for the Tsk mutation. We now demonstrate that the Tsk chromosome harbors a 30- to 40-kb genomic duplication within the Fbn1 gene that results in a larger than normal in-frame Fbn1 transcript. These findings provide hypotheses to explain some of the phenotypic characteristics of Tskl + mice and the lethality of Tsk/Tsk embryos.

Mutation in fibrillin-1 and the Marfanoid-craniosynostosis (Shprintzen-Goldberg) syndrome

Recent reports have described a distinct and recurrent pattern of systemic malformation that associates craniosynostosis and neurodevelopmental abnormalities with many clinical features of the Marfan syndrome (MFS), an autosomal dominant disorder of the extracellular microfibril caused by defects in the gene encoding fibrillin-1, FBN1 (ref. 8). Additional common findings include other craniofacial anomalies, hypotonia, obstructive apnea, foot deformity, and congenital weakness of the abdominal wall. So far, only 11 cases have been reported precluding the assignment of definitive diagnostic criteria. While it remains unclear whether these cases represent a discrete clinical entity with a single aetiology, they have been pragmatically grouped under the rubric Marfanoid-craniosynostosis or Shprintzen-Goldberg syndrome (SGS). Because of the significant clinical overlap between MFS and SGS, we proposed that they may be caused by allelic mutations. We now report two SGS patients who harbour mutations in FBN1. While it remains unclear whether these mutations are sufficient for the clinical expression of the entire SGS phenotype, these data suggest a role for fibrillin-1 in early craniofacial and central nervous system development. Our recent observation that FBN1 transcript is expressed as early as the 8-cell stage of human embryogenesis is consistent with this hypothesis.