Uneven X inactivation in a female monozygotic twin pair with Fabry disease and discordant expression of a novel mutation in the alpha-galactosidase A gene

Fabry Disease: Cardiac Implications and Molecular Mechanisms

PURPOSE OF REVIEW

This review explores the interplay among metabolic dysfunction, oxidative stress, inflammation, and fibrosis in Fabry disease, focusing on their potential implications for cardiac involvement. We aim to discuss the biochemical processes that operate in parallel to sphingolipid accumulation and contribute to disease pathogenesis, emphasizing the importance of a comprehensive understanding of these processes.

RECENT FINDINGS

Beyond sphingolipid accumulation, emerging studies have revealed that mitochondrial dysfunction, oxidative stress, and chronic inflammation could be significant contributors to Fabry disease and cardiac involvement. These factors promote cardiac remodeling and fibrosis and may predispose Fabry patients to conduction disturbances, ventricular arrhythmias, and heart failure. While current treatments, such as enzyme replacement therapy and pharmacological chaperones, address disease progression and symptoms, their effectiveness is limited. Our review uncovers the potential relationships among metabolic disturbances, oxidative stress, inflammation, and fibrosis in Fabry disease-related cardiac complications. Current findings suggest that beyond sphingolipid accumulation, other mechanisms may significantly contribute to disease pathogenesis. This prompts the exploration of innovative therapeutic strategies and underscores the importance of a holistic approach to understanding and managing Fabry disease.

Discordant renal progression of Fabry disease in male monozygotic twins: a case report

Background: Fabry disease (FD) is a rare X-linked lysosomal storage disease caused by mutations in the GLA gene that encodes α-galactosidase A (α-GAL). Clinical phenotypes tend to vary in monozygotic female twins because mutations are located on the X-chromosome, whereas similar phenotypes are found in male monozygotic twins. Here we report the case of male monozygotic twins with FD presenting with distinguishable renal phenotypes. Case: A 49-year-old male patient who visited the hospital with proteinuria 14 years prior was readmitted for the same issue. His monozygotic twin brother had started hemodialysis 6 months prior due to renal failure of unknown origin. The patient's renal function was within the normal range, while his spot urine protein-to-creatinine ratio was 557 mg/g. Echocardiography revealed left ventricular hypertrophy (LVH). The findings of a renal biopsy were consistent with FD. Genetic testing identified a c.656T>C mutation in the GLA gene, and α-GAL activity was significantly decreased. Genetic screening of his family clarified that his mother, older sister, twin brother, and his daughter had the same genetic mutations. The patient received enzyme replacement therapy 34 times. Subsequently, migalastat was initiated that continues today. Renal function and proteinuria remain stable, and the LVH has mildly improved. Conclusion: This is the first case of male monozygotic twins expressing different progressions of FD. Our findings demonstrate the possibility that environmental or epigenetic factors may critically influence genotype-phenotype discordance.

X-Chromosome Inactivation and Related Diseases

X-chromosome inactivation (XCI) is the form of dosage compensation in mammalian female cells to balance X-linked gene expression levels of the two sexes. Many diseases are related to XCI due to inactivation escape and skewing, and the symptoms and severity of these diseases also largely depend on the status of XCI. They can be divided into 3 types: X-linked diseases, diseases that are affected by XCI escape, and X-chromosome aneuploidy. Here, we review representative diseases in terms of their definition, symptoms, and XCI’s role in the pathogenesis of these diseases.

Pitfalls of X-chromosome inactivation testing in females with Fabry disease

Fabry disease (FD) is an X-linked lysosomal storage disorder caused by mutations in the GLA gene encoding alpha-galactosidase A (AGAL). The impact of X-chromosome inactivation (XCI) on the phenotype of female FD patients remains unclear. In this study we aimed to determine pitfalls of XCI testing in a cohort of 35 female FD patients. XCI was assessed by two methylation-based and two allele-specific expression assays. The results correlated, although some variance among the four assays was observed. GLA transcript analyses identified crossing-over in three patients and detected mRNA instability in three out of four analyzed null alleles. AGAL activity correlated with XCI pattern and was not influenced by the mutation type or by reduced mRNA stability. Therefore, AGAL activity may help to detect crossing-over in patients with unstable GLA alleles. Tissue-specific XCI patterns in six patients, and age-related changes in two patients were observed. To avoid misinterpretation of XCI results in female FD patients we show that (i) a combination of several XCI assays generates more reliable results and minimizes possible biases; (ii) correlating XCI to GLA expression and AGAL activity facilitates identification of cross-over events; (iii) age- and tissue-related XCI specificities of XCI patterning should be considered.

Circulating miR-184 is a potential predictive biomarker of cardiac damage in Anderson-Fabry disease

Enzyme replacement therapy (ERT) is a mainstay of treatment for Anderson-Fabry disease (AFD), a pathology with negative effects on the heart and kidneys. However, no reliable biomarkers are available to monitor its efficacy. Therefore, we tested a panel of four microRNAs linked with cardiac and renal damage in order to identify a novel biomarker associated with AFD and modulated by ERT. To this end, 60 patients with a definite diagnosis of AFD and on chronic ERT, and 29 age- and sex-matched healthy individuals, were enrolled by two Italian university hospitals. Only miR-184 met both conditions: its level discriminated untreated AFD patients from healthy individuals (c-statistic = 0.7522), and it was upregulated upon ERT (P < 0.001). On multivariable analysis, miR-184 was independently and inversely associated with a higher risk of cardiac damage (odds ratio = 0.86; 95% confidence interval [CI] = 0.76-0.98; P = 0.026). Adding miR-184 to a comprehensive clinical model improved the prediction of cardiac damage in terms of global model fit, calibration, discrimination, and classification accuracy (continuous net reclassification improvement = 0.917, P < 0.001; integrated discrimination improvement [IDI] = 0.105, P = 0.017; relative IDI = 0.221, 95% CI = 0.002-0.356). Thus, miR-184 is a circulating biomarker of AFD that changes after ERT. Assessment of its level in plasma could be clinically valuable in improving the prediction of cardiac damage in AFD patients.

Plasma Globotriaosylsphingosine and α-Galactosidase A Activity as a Combined Screening Biomarker for Fabry Disease in a Large Japanese Cohort

Fabry disease is an X-linked disorder of α-galactosidase A (GLA) deficiency. Our previous interim analysis (1 July 2014 to 31 December 2015) revealed plasma globotriaosylsphingosine as a promising primary screening biomarker for Fabry disease probands. Herein, we report the final results, including patients enrolled from 1 January to 31 December 2016 for evaluating the potential of plasma globotriaosylsphingosine and GLA activity as a combined screening marker. We screened 5691 patients (3439 males) referred from 237 Japanese specialty clinics based on clinical findings suggestive of Fabry disease using plasma globotriaosylsphingosine and GLA activity as primary screening markers, and GLA variant status as a secondary screening marker. Of the 14 males who tested positive in the globotriaosylsphingosine screen (≥2.0 ng/mL), 11 with low GLA activity (<4.0 nmol/h/mL) displayed GLA variants (four classic, seven late-onset) and one with normal GLA activity and no pathogenic variant displayed lamellar bodies in affected organs, indicating late-onset biopsy-proven Fabry disease. Of the 19 females who tested positive in the globotriaosylsphingosine screen, eight with low GLA activity displayed GLA variants (six classic, two late-onset) and five with normal GLA activity displayed a GLA variant (one classic) and no pathogenic variant (four late-onset biopsy-proven). The combination of plasma globotriaosylsphingosine and GLA activity can be a primary screening biomarker for classic, late-onset, and late-onset biopsy-proven Fabry disease probands.

Dosage Compensation in Females with X-Linked Metabolic Disorders

Through the use of new genomic and metabolomic technologies, our comprehension of the molecular and biochemical etiologies of genetic disorders is rapidly expanding, and so are insights into their varying phenotypes. Dosage compensation (lyonization) is an epigenetic mechanism that balances the expression of genes on heteromorphic sex chromosomes. Many studies in the literature have suggested a profound influence of this phenomenon on the manifestation of X-linked disorders in females. In this review, we summarize the clinical and genetic findings in female heterozygotic carriers of a pathogenic variant in one of ten selected X-linked genes whose defects result in metabolic disorders.

Hypertrophy of unaffected cardiomyocytes correlates with severity of cardiomyopathy in female patients with Fabry disease

Aim

To investigate the contribution of unaffected cardiomyocytes in Fabry disease cardiomyopathy.

Findings

Left ventricular (LV) endomyocardial biopsies from twenty-four females (mean age 53 ± 11 ys) with Fabry disease cardiomyopathy were studied. Diagnosis of FD was based on the presence of pathogenic GLA mutation, Patients were divided in four groups according with LV maximal wall thickness (MWT): group 1 MWT ≤ 10.5 mm, group 2 MWT 10.5–15 mm, group 3 MWT 16–20 mm, group 4 MWT > 20 mm. At histology mosaic of affected and unaffected cardiomyocytes was documented. Unaffected myocytes’ size ranged from normal to severe hypertrophy. Hypertrophy of unaffected cardiomyocytes correlated with severity of MWT (p < 0.0001, Sperman r 0,95). Hypertrophy of unaffected myocytes appear to concur to progression and severity of FDCM. It is likely a paracrine role from neighboring affected myocytes.

DNA methylation impact on Fabry disease

BACKGROUND

Fabry disease (FD) is a rare X-linked disease caused by mutations in GLA gene with consequent lysosomal accumulation of globotriaosylceramide (Gb3). Women with FD often show highly heterogeneous symptoms that can manifest from mild to severe phenotype.

MAIN BODY

The phenotypic variability of the clinical manifestations in heterozygous women with FD mainly depends on the degree and direction of inactivation of the X chromosome. Classical approaches to measure XCI skewness might be not sufficient to explain disease manifestation in women. In addition to unbalanced XCI, allele-specific DNA methylation at promoter of GLA gene may influence the expression levels of the mutated allele, thus impacting the onset and the outcome of FD. In this regard, analyses of DNA methylation at GLA promoter, performed by approaches allowing distinction between mutated and non-mutated allele, may be much more informative. The aim of this review is to critically evaluate recent literature articles addressing the potential role of DNA methylation in the context of FD. Although up to date relatively few works have addressed this point, reviewing all pertinent studies may help to evaluate the importance of DNA methylation analysis in FD and to develop new research and technologies aimed to predict whether the carrier females will develop symptoms.

CONCLUSIONS

Relatively few studies have addressed the complexity of DNA methylation landscape in FD that remains poorly investigated. The hope for the future is that ad hoc and ultradeep methylation analyses of GLA gene will provide epigenetic signatures able to predict whether pre-symptomatic female carriers will develop symptoms thus helping timely interventions.

Biomarkers of Fabry Nephropathy: Review and Future Perspective

Progressive nephropathy is one of the main features of Fabry disease, which largely contributes to the overall morbidity and mortality burden of the disease. Due to the lack of specific biomarkers, the heterogeneity of the disease, and unspecific symptoms, diagnosis is often delayed. Clinical presentation in individual patients varies widely, even in patients from the same family carrying the same pathogenic GLA variant. Therefore, it is reasonable to anticipate that additional genomic, transcriptomic, proteomic, and metabolomics factors influence the manifestation and progression of the disease. The aim of this article is to provide an overview of nephropathy in Fabry patients and the biomarkers currently used in the diagnosis and follow-up. Current biomarkers are associated with late signs of kidney damage. Therefore, there is a need to identify biomarkers associated with early stages of kidney damage that would enable early diagnosis, which is crucial for effective treatment and prevention of severe irreversible complications. Recent advances in sequencing and -omics technologies have led to several studies investigating new biomarkers. We will provide an overview of the novel biomarkers, critically evaluate their clinical utility, and propose future perspectives, which we believe might be in their integration.

Differential phenotypic expression of a novel PDHA1 mutation in a female monozygotic twin pair

Pyruvate dehydrogenase complex (PDC) deficiency caused by mutations in the X-linked PDHA1 gene has a broad clinical presentation, and the pattern of X-chromosome inactivation has been proposed as a major factor contributing to its variable expressivity in heterozygous females. Here, we report the first set of monozygotic twin females with PDC deficiency, caused by a novel, de novo heterozygous missense mutation in exon 11 of PDHA1 (NM_000284.3: c.1100A>T). Both twins presented in infancy with a similar clinical phenotype including developmental delay, episodes of hypotonia or encephalopathy, epilepsy, and slowly progressive motor impairment due to pyramidal, extrapyramidal, and cerebellar involvement. However, they exhibited clear differences in disease severity that correlated well with residual PDC activities (approximately 60% and 20% of mean control values, respectively) and levels of immunoreactive E1α subunit in cultured skin fibroblasts. To address whether the observed clinical and biochemical differences could be explained by the pattern of X-chromosome inactivation, we undertook an androgen receptor assay in peripheral blood. In the less severely affected twin, a significant bias in the relative activity of the two X chromosomes with a ratio of approximately 75:25 was detected, while the ratio was close to 50:50 in the other twin. Although it may be difficult to extrapolate these results to other tissues, our observation provides further support to the hypothesis that the pattern of X-chromosome inactivation may influence the phenotypic expression of the same mutation in heterozygous females and broadens the clinical and genetic spectrum of PDC deficiency.

UniProt genomic mapping for deciphering functional effects of missense variants

Understanding the association of genetic variation with its functional consequences in proteins is essential for the interpretation of genomic data and identifying causal variants in diseases. Integration of protein function knowledge with genome annotation can assist in rapidly comprehending genetic variation within complex biological processes. Here, we describe mapping UniProtKB human sequences and positional annotations, such as active sites, binding sites, and variants to the human genome (GRCh38) and the release of a public genome track hub for genome browsers. To demonstrate the power of combining protein annotations with genome annotations for functional interpretation of variants, we present specific biological examples in disease-related genes and proteins. Computational comparisons of UniProtKB annotations and protein variants with ClinVar clinically annotated single nucleotide polymorphism (SNP) data show that 32% of UniProtKB variants colocate with 8% of ClinVar SNPs. The majority of colocated UniProtKB disease-associated variants (86%) map to 'pathogenic' ClinVar SNPs. UniProt and ClinVar are collaborating to provide a unified clinical variant annotation for genomic, protein, and clinical researchers. The genome track hubs, and related UniProtKB files, are downloadable from the UniProt FTP site and discoverable as public track hubs at the UCSC and Ensembl genome browsers.

Effectiveness of plasma lyso-Gb3 as a biomarker for selecting high-risk patients with Fabry disease from multispecialty clinics for genetic analysis

PURPOSE

Plasma globotriaosylsphingosine (lyso-Gb3) is a promising secondary screening biomarker for Fabry disease. Here, we examined its applicability as a primary screening biomarker for classic and late-onset Fabry disease in males and females.

METHODS

Between 1 July 2014 and 31 December 2015, we screened 2,359 patients (1,324 males) referred from 168 Japanese specialty clinics (cardiology, nephrology, neurology, and pediatrics), based on clinical symptoms suggestive of Fabry disease. We used the plasma lyso-Gb3 concentration, α-galactosidase A (α-Gal A) activity, and analysis of the α-Gal A gene (GLA) for primary and secondary screens, respectively.

RESULTS

Of 8 males with elevated lyso-Gb3 levels (≥2.0 ng ml-1) and low α-Gal A activity (≤4.0 nmol h-1 ml-1), 7 presented a GLA mutation (2 classic and 5 late-onset). Of 14 females with elevated lyso-Gb3, 7 displayed low α-Gal A activity (5 with GLA mutations; 4 classic and 1 late-onset) and 7 exhibited normal α-Gal A activity (1 with a classic GLA mutation and 3 with genetic variants of uncertain significance).

CONCLUSION

Plasma lyso-Gb3 is a potential primary screening biomarker for classic and late-onset Fabry disease probands.

Phenotype and biochemical heterogeneity in late onset Fabry disease defined by N215S mutation

BACKGROUND

Fabry disease (FD) results from X-linked inheritance of a mutation in the GLA gene, encoding for alpha galactosidase A, and is characterized by heterogeneous clinical manifestations. Two phenotypes have been described "Classic" and "late onset" which cannot be predicted exclusively by genotype. The latter has been considered an attenuated form of the disease often affecting a single organ system commonly the heart. Recent studies have demonstrated that cardiac outcomes are similar in patients with classic and late onset mutations. In this study we investigate the relationship between clinical heterogeneity and plasma lyso-Gb3 in a large single centre cohort of N215S patients and compare this to patients with other mutations.

METHODS

In this single-centre, retrospective, cross-sectional study we analysed a cohort of 251 FD patients: 84 N215S mutation (37 males) and 167 non-N215S mutations (58 males). The Mainz severity score index (MSSI) was used as an index of overall disease severity. Cardiac function and morphology were assessed by electrocardiogram and echocardiogram. Left ventricular mass was calculated using the Devereux formula and the left ventricular mass index (LVMI) calculated to adjust for height (g/m2.7). The presence of white matter lesions was assessed by cerebral MRI or computed tomography (CT). GFR was measured by radio-isotope (chromium-EDTA) method and adjusted for patient height (ml/min/m2.7), and urinary protein quantification was undertaken by 24 hour urine collection. Plasma globotriaosylsphingosine (lyso-Gb3) was analysed prior to ERT in 84 patients.

RESULTS

N215S patients showed later symptom onset (males: p< 0.0001, females: p<0.03), later development of left ventricular hypertrophy (LVH) (median survival without LVH: 41 (non-N215S) vs. 64 (N215S) years, p< 0.0001), later development of proteinuria (median survival without proteinuria 43 (non-N215S) vs 71 years (N215S), p< 0.0001), later occurrence of cerebrovascular events (stroke/ Transient Ischaemic Attacks (TIA); median survival without stroke: 74 years (non-N215S) vs. not reached (N215S), p< 0.02), later decline in renal function to GFR <60 ml/min/1.73m2 (median survival: 56 (non-N215S) vs. 72 (N215S) years, p< 0.01), and greater overall survival (median survival 81 (N215S) vs. 66 (non-N215S) years, p< 0.0006). Lyso-Gb3 was found to be less elevated in N215S compared to non-N215S male and female patients. However, the N215S population eventually reached an overall severity measured by MSSI comparable to the non-N215S without equivalent elevation of lyso-Gb3 (means: 6.7 vs. 74.3 nmol/L, p < 0.001). In addition, N215S patients showed strong correlations between lyso-Gb3 levels and LVMI, GFR, and MSSI. These associations became stronger when we investigated individuals' life time exposure to lyso-Gb3 (calculated as [lyso-Gb3]*age): MSSI (r2 = 0.88, p< 0.0001), LVMI (r2 = 0.59, p< 0.005), and GFR (r2 = 0.75, p = 0.0001).

CONCLUSION

These results demonstrate that the N215S mutation results in a late onset phenotype involving the heart and other organs. Correlations between clinical manifestations and plasma lyso-Gb3 variations in this group suggest a Fabry-relevant disease mechanism for the heterogeneity observed in this group.

The role of epigenetics in lysosomal storage disorders: Uncharted territory

The study of the contribution of epigenetic mechanisms, including DNA methylation, histone modifications, and microRNAs, to human disease has enhanced our understanding of different cellular processes and diseased states, as well as the effect of environmental factors on phenotypic outcomes. Epigenetic studies may be particularly relevant in evaluating the clinical heterogeneity observed in monogenic disorders. The lysosomal storage disorders are Mendelian disorders characterized by a wide spectrum of associated phenotypes, ranging from neonatal presentations to symptoms that develop in late adulthood. Some lack a tight genotype/phenotype correlation. While epigenetics may explain some of the discordant phenotypes encountered in patients with the same lysosomal storage disorder, especially among patients sharing the same genotype, to date, few studies have focused on these mechanisms. We review three common epigenetic mechanisms, DNA methylation, histone modifications, and microRNAs, and highlight their applications to phenotypic variation and therapeutics. Three specific lysosomal storage diseases, Gaucher disease, Fabry disease, and Niemann-Pick type C disease are presented as prototypical disorders with vast clinical heterogeneity that may be impacted by epigenetics. Our goal is to motivate researchers to consider epigenetics as a mechanism to explain the complexities of biological functions and pathologies of these rare disorders.

Female Fabry disease patients and X-chromosome inactivation

Fabry disease is an X-linked inherited lysosomal storage disorder caused by mutations in the gene encoding α-galactosidase A (GLA). Once it was thought to affect only hemizygous males. Over the last fifteen years, research has shown that most females carrying mutated allele also develop symptoms, demonstrating a wide range of disease severity, from a virtually asymptomatic to more classical profile, with cardiac, renal, and cerebrovascular manifestations. This variable expression in females is thought to be influenced by the process of X-chromosome inactivation (XCI). The aim of this study was to assess severity of the clinical phenotype, to analyze XCI patterns, and to estimate their effect on disease manifestation in twelve female Fabry disease patients from five unrelated Polish families. Our analyses revealed that patients presented with the broad range of disease expression - from mild to severe, and their clinical involvement did not correlate with XCI profiles. Female carriers of the mutation in the GLA gene with the random XCI may present with the wide range of disease signs and symptoms. Thus, XCI is not a main factor in the phenotype variability of Fabry disease manifestation in heterozygous females.

Different renal phenotypes in related adult males with Fabry disease with the same classic genotype

Background

Fabry disease related patients with classical mutation usually exhibit similar severe phenotype especially concerning renal manifestation.

Methods

A dry blood spot screening (DBS) and the DNA analysis has been performed in a 48‐year‐old man (Patient 1) because of paresthesia.

Results

The DBS revealed absent leukocyte α‐Gal A enzyme activity while DNA analysis identified the I354K mutation. Serum creatinine and e‐GFR were in normal range and also albuminuria and proteinuria were absent. The brain MRI showed ischemic lesions and a diffuse focus of gliosis in the white matter, while the echocardiogram showed a left ventricular hypertrophy. The renal biopsy performed in the case index showed a massive deposition of zebra bodies. By a familiar investigation, it was recognized that his brother (Patient 2) died 2 years before from sudden death syndrome at the age of 49. He had suffered sporadic and undiagnosed pain at the extremities, a prior cataract, bilateral neurosensorial hearing loss and left ventricular hypertrophy on Echocardiogram. His previous laboratory examinations revealed a normal serum creatinine and the absence of proteinuria. Pedigree analysis of the brothers revealed a high disease burden among family members, with an affected cousin (Patient 3) who progressed early to end‐stage renal disease (ESRD) that required renal transplantation.

Conclusions

Here we describe the clinical history of three adult male members of the same family with the same genotype who manifested different presentation and progression of the disease, particularly concerning the renal involvement.

Fabry's disease: an example of cardiorenal syndrome type 5

Cardiorenal syndrome type 5 (CRS-5) includes conditions where there is a simultaneous involvement of the heart and kidney from a systemic disorder. This is a bilateral organ cross talk. Fabry's disease (FD) is a devastating progressive inborn error of metabolism with lysosomal glycosphingolipid deposition in variety of cell types, capillary endothelial cells, renal, cardiac and nerve cells. Basic effect is absent or deficient activity of lysosomal exoglycohydrolase a-galactosidase A. Renal involvement consists of proteinuria, isosthenuria, altered tubular function, presenting in second or third decade leading to azotemia and end-stage renal disease in third to fifth decade mainly due to irreversible changes to glomerular, tubular and vascular structures, especially highlighted by podocytes foot process effacement. Cardiac involvement consists of left ventricular hypertrophy, right ventricular hypertrophy, arrhythmias (sinus node and conduction system impairment), diastolic dysfunction, myocardial ischemia, infarction, transmural replacement fibrosis, congestive heart failure and cardiac death. Management of FD is based on enzymatic replacement therapy and control of renal (with anti-proteinuric agents such as angiotensin-converting enzyme inhibitors-and/or angiotensin II receptor blockers), brain (coated aspirin, clopidogrel and statin to prevent strokes) and heart complications (calcium channel blockers for ischemic cardiomyopathy, warfarin and amiodarone or cardioverter device for arrhythmias).

Novel GLA Deletion in a Cypriot Female Presenting with Cornea Verticillata

Fabry disease is an X-linked lysosomal storage disorder resulting from a deficiency of the hydrolytic enzyme α-galactosidase A (α-Gal-A). It is characterized by progressive lysosomal accumulation of globotriaosylceramide (Gb3) and multisystem pathology, affecting the skin, nervous and cerebrovascular systems, kidneys, and heart. Heterozygous females typically exhibit milder symptoms and a later age of onset than males. Rarely, they may be relatively asymptomatic throughout a normal life span or may have symptoms as severe as those observed in males with the classic phenotype. We report on a 17-year-old female in whom cornea verticillata was found during a routine ophthalmological examination but with no other clinical symptoms. Leucocyte α-galactosidase activity was within the overlap range between Fabry heterozygotes and normal controls. Sanger sequencing of the GLA gene failed to reveal any pathogenic variants. Multiplex Ligation-dependent Probe Amplification (MLPA) analysis revealed a deletion of exon 7. Using a long-range PCR walking approach, we managed to identify the deletion breakpoints. The deletion spans 1182 bp, with its 5' end located within exon 6 of the GLA gene and its 3' end located 612 bp downstream of exon 7. This finding represents a novel deletion identified in the first reported Cypriot female carrier of Fabry disease.

Pharmacological chaperones as therapeutics for lysosomal storage diseases

Lysosomal enzymes are responsible for the degradation of a wide variety of glycolipids, oligosaccharides, proteins, and glycoproteins. Inherited mutations in the genes that encode these proteins can lead to reduced stability of newly synthesized lysosomal enzymes. While often catalytically competent, the mutated enzymes are unable to efficiently pass the quality control mechanisms of the endoplasmic reticulum, resulting in reduced lysosomal trafficking, substrate accumulation, and cellular dysfunction. Pharmacological chaperones (PCs) are small molecules that bind and stabilize mutant lysosomal enzymes, thereby allowing proper cellular translocation. Such compounds have been shown to increase enzyme activity and reduce substrate burden in a number of preclinical models and clinical studies. In this Perspective, we review several of the lysosomal diseases for which PCs have been studied and the SAR of the various classes of molecules.

Copy number changes on the X chromosome in women with and without highly skewed X-chromosome inactivation

AIM

To test the hypothesis that microdeletions or microduplications below the resolution of a standard karyotype may be a significant cause of highly skewed X-inactivation (HSXI) in women without a cytogenetically detected X-chromosome anomaly.

METHODS

Cases were women with HSXI, defined as ≥85% of cells in a blood sample with the same active allele at the HUMARA locus. The skewing in controls ranged from 50 to <75%. We performed an SNP microarray analysis using the Affymetrix 6.0 platform for 45 cases and 45 controls.

RESULTS

Cases and controls did not differ in the frequency of X-chromosome copy number changes ≥100 kb or in the frequency of copy number changes that contained genes. However, one woman with HSXI >90% in blood and left and right buccal smears had a 5.5-Mb deletion in Xp22.2p22.1. This deletion could affect the viability of male conceptions and may have led to the dysmorphology found in female carriers.

CONCLUSION

HSXI in a blood sample is rarely due to X-chromosome copy number changes detectable by microarray.

Three new loci for determining x chromosome inactivation patterns

The analysis of X chromosome inactivation (XCI) patterns is a widely used diagnostic tool in clinical practice when investigating X-linked diseases. The most commonly used assay to determine XCI patterns takes advantage of a locus within the androgen receptor (AR) gene. This PCR-based assay relies on two differentially methylated restriction enzyme sites (HpaII) and a polymorphic repeat located within this locus. Although highly informative, this locus is not always sufficient to evaluate the X-inactivation status in X-linked disorders. We have identified three new loci that can be used to determine XCI patterns in a methylation-sensitive PCR-based assay. All three loci contain polymorphic repeats and a methylation-sensitive restriction enzyme (HpaII) site, methylation of which was shown to correlate with XCI. DNA from 60 females was used to estimate the heterozygosity of these new loci. The reliability of the loci was validated by showing a high correlation between the results obtained by employing the new loci and the AR locus using DNA from 15 females who were informative for all four loci. Altogether, we show that these loci can be applied easily in molecular diagnostic laboratories, either as a supplement or as an alternative to the existing AR assay.

Fabry disease

Fabry disease (FD) is a progressive, X-linked inherited disorder of glycosphingolipid metabolism due to deficient or absent lysosomal α-galactosidase A activity. FD is pan-ethnic and the reported annual incidence of 1 in 100,000 may underestimate the true prevalence of the disease. Classically affected hemizygous males, with no residual α-galactosidase A activity may display all the characteristic neurological (pain), cutaneous (angiokeratoma), renal (proteinuria, kidney failure), cardiovascular (cardiomyopathy, arrhythmia), cochleo-vestibular and cerebrovascular (transient ischemic attacks, strokes) signs of the disease while heterozygous females have symptoms ranging from very mild to severe. Deficient activity of lysosomal α-galactosidase A results in progressive accumulation of globotriaosylceramide within lysosomes, believed to trigger a cascade of cellular events. Demonstration of marked α-galactosidase A deficiency is the definitive method for the diagnosis of hemizygous males. Enzyme analysis may occasionnally help to detect heterozygotes but is often inconclusive due to random X-chromosomal inactivation so that molecular testing (genotyping) of females is mandatory. In childhood, other possible causes of pain such as rheumatoid arthritis and 'growing pains' must be ruled out. In adulthood, multiple sclerosis is sometimes considered. Prenatal diagnosis, available by determination of enzyme activity or DNA testing in chorionic villi or cultured amniotic cells is, for ethical reasons, only considered in male fetuses. Pre-implantation diagnosis is possible. The existence of atypical variants and the availability of a specific therapy singularly complicate genetic counseling. A disease-specific therapeutic option - enzyme replacement therapy using recombinant human α-galactosidase A - has been recently introduced and its long term outcome is currently still being investigated. Conventional management consists of pain relief with analgesic drugs, nephroprotection (angiotensin converting enzyme inhibitors and angiotensin receptors blockers) and antiarrhythmic agents, whereas dialysis or renal transplantation are available for patients experiencing end-stage renal failure. With age, progressive damage to vital organ systems develops and at some point, organs may start to fail in functioning. End-stage renal disease and life-threatening cardiovascular or cerebrovascular complications limit life-expectancy of untreated males and females with reductions of 20 and 10 years, respectively, as compared to the general population. While there is increasing evidence that long-term enzyme therapy can halt disease progression, the importance of adjunctive therapies should be emphasized and the possibility of developing an oral therapy drives research forward into active site specific chaperones.

Familial Simpson-Golabi-Behmel syndrome: studies of X-chromosome inactivation and clinical phenotypes in two female individuals with GPC3 mutations

Simpson-Golabi-Behmel syndrome (SGBS) is an overgrowth/multiple congenital anomalies syndrome with an X-linked inheritance. Most cases of SGBS are attributed to mutations in the glypican 3-gene (GPC3), which is highly expressed in the mesodermal embryonic tissues and involves in a local growth regulation. Typical clinical features include pre/postnatal overgrowth, developmental delay, macrocephaly, characteristic facies with prominent eyes and macroglossia, diaphragmatic hernia, congenital heart defects, kidney anomalies, and skeletal anomalies. Obligate carrier females with GPC3 mutations are usually asymptomatic or with mild symptoms. It is thought that skewed X-inactivation is the underlining mechanism for the female patients to present with findings of SGBS. We identified three siblings with typical SGBS (two male and one female cases) and their mother with very mild symptoms in a family carrying c.256C>T (p.Arg86X) mutation in GPC3. X-inactivation studies on the androgen-receptor gene (AR) and the Fragile XE (FRAXE) gene were performed with blood, buccal swabs, and fibroblasts in the carrier females. The studies with blood showed moderately skewed X-inactivation with paternal X-chromosome being preferentially inactivated (71-80% inactivated) in the female patient with SGBS and no skewing was shown in the mother with very mild symptoms. The X-inactivation studies in the mother showed inactivation of the X-chromosome with the mutation by 57%. This suggests that loss of the functional GPC3 protein by 43% is closed to the threshold to develop the SGBS phenotype. Studies with buccal swabs and fibroblasts failed to show different X-inactivation patterns between the two female individuals.

Identical but not the same: the value of discordant monozygotic twins in genetic research

Monozygotic (MZ) twins show remarkable resemblance in many aspects of behavior, health, and disease. Until recently, MZ twins were usually called "genetically identical"; however, evidence for genetic and epigenetic differences within rare MZ twin pairs has accumulated. Here, we summarize the literature on MZ twins discordant for Mendelian inherited disorders and chromosomal abnormalities. A systematic literature search for English articles on discordant MZ twin pairs was performed in Web of Science and PubMed. A total number of 2,016 publications were retrieved and reviewed and 439 reports were retained. Discordant MZ twin pairs are informative in respect to variability of phenotypic expression, pathogenetic mechanisms, epigenetics, and post-zygotic mutagenesis and may serve as a model for research on genetic defects. The analysis of single discordant MZ twin pairs may represent an elegant approach to identify genes in inherited disorders.

How well does urinary lyso-Gb3 function as a biomarker in Fabry disease?

BACKGROUND

Fabry disease is characterized by accumulation of glycosphingolipids, such as globotriaosylceramide (Gb(3)), in many tissues and body fluids. A novel plasma biomarker, globotriaosylsphingosine (lyso-Gb(3)), is increased in patients with the disease. Until now, lyso-Gb(3) was not detectable in urine, possibly because of the presence of interfering compounds.

METHODS

We undertook to: 1) characterize lyso-Gb(3) in urine; 2) develop a method to quantitate urinary lyso-Gb(3) by mass spectrometry; 3) evaluate urinary lyso-Gb(3) as a potential biomarker for Fabry disease; and 4) determine whether lyso-Gb(3) is an inhibitor of α-galactosidase A activity. We analyzed urinary lyso-Gb(3) from 83 Fabry patients and 77 healthy age-matched controls.

RESULTS

The intraday and interday bias and precision of the method were <15%. Increases in lyso-Gb(3)/creatinine correlated with the concentrations of Gb(3) (r(2)=0.43), type of mutations (p=0.0006), gender (p<0.0001) and enzyme replacement therapy status (p=0.0012). Urine from healthy controls contained no detectable lyso-Gb(3). Lyso-Gb(3) did not inhibit GLA activity in dried blood spots. Increased urinary excretion of lyso-Gb(3) of Fabry patients correlated well with a number of indicators of disease severity.

CONCLUSION

Lyso-Gb(3) is a reliable independent biomarker for clinically important characteristics of Fabry disease.

Expression of the disease on female carriers of X-linked lysosomal disorders: a brief review

Most lysosomal diseases (LD) are inherited as autosomal recessive traits, but two important conditions have X-linked inheritance: Fabry disease and Mucopolysaccharidosis II (MPS II). These two diseases show a very different pattern regarding expression on heterozygotes, which does not seem to be explained by the X-inactivation mechanism only. While MPS II heterozygotes are asymptomatic in most instances, in Fabry disease most of female carriers show some disease manifestation, which is sometimes severe. It is known that there is a major difference among X-linked diseases depending on the cell autonomy of the gene product involved and, therefore, on the occurrence of cross-correction. Since lysosomal enzymes are usually secreted and uptaken by neighbor cells, the different findings between MPS II and Fabry disease heterozygotes can also be due to different efficiency of cross-correction (higher in MPS II and lower in Fabry disease). In this paper, we review these two X-linked LD in order to discuss the mechanisms that could explain the different rates of penetrance and expressivity observed in the heterozygotes; this could be helpful to better understand the expression of X-linked traits.

Mutation patterns in human α-galactosidase A

A way to study the mutation pattern is to convert a 20-letter protein sequence into a scalar protein sequence, because the 20-letter protein sequence is neither vector nor scalar while a promising way to study patterns is in numerical domain. In this study, we use the amino-acid pair predictability to convert α-galactosidase A with its 137 mutations into scalar sequences, and analyse which amino-acid pairs are more sensitive to mutation. Our results show that the unpredictable amino-acid pairs are more sensitive to mutation, and the mutation trend is to narrow the difference between predicted and actual frequency of amino-acid pairs.

The pharmacological chaperone 1-deoxygalactonojirimycin reduces tissue globotriaosylceramide levels in a mouse model of Fabry disease

Fabry disease is an X-linked lysosomal storage disorder caused by a deficiency in alpha-galactosidase A (alpha-Gal A) activity and subsequent accumulation of the substrate globotriaosylceramide (GL-3), which contributes to disease pathology. The pharmacological chaperone (PC) DGJ (1-deoxygalactonojirimycin) binds and stabilizes alpha-Gal A, increasing enzyme levels in cultured cells and in vivo. The ability of DGJ to reduce GL-3 in vivo was investigated using transgenic (Tg) mice that express a mutant form of human alpha-Gal A (R301Q) on a knockout background (Tg/KO), which leads to GL-3 accumulation in disease-relevant tissues. Four-week daily oral administration of DGJ to Tg/KO mice resulted in significant and dose-dependent increases in alpha-Gal A activity, with concomitant GL-3 reduction in skin, heart, kidney, brain, and plasma; 24-week administration resulted in even greater reductions. Compared to daily administration, less frequent DGJ administration, including repeated cycles of 4 days with DGJ followed by 3 days without or every other day with DGJ, resulted in even greater GL-3 reductions that were comparable to those obtained with Fabrazyme. Collectively, these data indicate that oral administration of DGJ increases mutant alpha-Gal A activity and reduces GL-3 in disease-relevant tissues in Tg/KO mice, and thus merits further evaluation as a treatment for Fabry disease.

Skewed X chromosome inactivation and trisomic spontaneous abortion: no association

Several studies suggest that highly skewed X chromosome inactivation (HSXI) is associated with recurrent spontaneous abortion. We hypothesized that this association reflects an increased rate of trisomic conceptions due to anomalies on the X chromosome that lead both to HSXI and to a diminished oocyte pool. We compared the distribution of X chromosome inactivation (XCI) skewing percentages (range: 50%-100%) among women with spontaneous abortions in four karyotype groups-trisomy (n = 154), chromosomally normal male (n = 43), chromosomally normal female (n = 38), nontrisomic chromosomally abnormal (n = 61)-to the distribution for age-matched controls with chromosomally normal births (n = 388). In secondary analyses, we subdivided the nontrisomic chromosomally abnormal group, divided trisomies by chromosome, and classified women by reproductive history. Our data support neither an association of HSXI with all trisomies nor an association of HSXI with chromosomally normal male spontaneous abortions. We also find no association between HSXI and recurrent abortion (n = 45).

X chromosome inactivation in clinical practice

X chromosome inactivation (XCI) is the transcriptional silencing of the majority of genes on one of the two X chromosomes in mammalian females. Females are, therefore, mosaics for two cell lines, one with the maternal X and one with the paternal X as the active chromosome. The relative proportion of the two cell lines, the X inactivation pattern, may be analyzed by simple assays in DNA from available tissues. This review focuses on medical issues related to XCI in X-linked disorders, and on the value of X inactivation analysis in clinical practice.

Proposed high-risk screening protocol for Fabry disease in patients with renal and vascular disease

Fabry disease is a complex, multisystemic and clinically heterogeneous disease with prominent urinary excretion of globotriaosylceramide (Gb(3)), the principal substrate of the deficient enzyme, alpha-galactosidase A. Some measure of specific treatment is possible with enzyme replacement therapy, which can be applied safely and effectively to Fabry patients. Incidence estimations of Fabry disease vary widely from 1:55 000 to 1:3000 male births. The true incidence is likely to be higher than originally thought, owing to the existence of milder variants of the disease. The main complications of Fabry disease are a 100-fold increased risk of ischaemic stroke, cardiac disease, a wide variety of arrhythmias, valvular dysfunction and cardiac vascular disease, as well as progressive renal failure usually associated with significant proteinuria. These clinical manifestations are non-specific and are often mistaken for symptoms of other disorders, thus complicating the confirmation of diagnosis. Other clinical features of the disease are often absent (angiokeratoma), subtle (corneal opacities and hypohidrosis), or unaccompanied by specific physical findings (acroparaesthesias) indicating the true nature of the underlying disease. We propose the hypothesis that alpha-galactosidase A deficiency is a modifiable cardiovascular risk factor in the general population. This hypothesis may be tested by a non-invasive high-risk screening protocol for Fabry patients with ischaemic strokes and a variety of cardiac, and renal complications. These patients would benefit from diagnosis, appropriate treatment, follow-up and surveillance. Early detection of Fabry patients would also benefit affected relatives, many of whom do not have a clear diagnosis of their clinical condition.

Treatment of Fabry disease with different dosing regimens of agalsidase: effects on antibody formation and GL-3

Two different enzyme preparations are used for the treatment of Fabry disease patients, agalsidase alpha (Replagal, Shire) and agalsidase beta (Fabrazyme, Genzyme). Therapeutic efficacy of both products has been variable probably due to differences in gender, severity, age and other patient characteristics. We studied the occurrence of alpha-Gal A antibodies and their effect on urinary and plasma globotriaosylceramide (GL-3), plasma chitotriosidase and clinical outcome in 52 patients after 12 months of treatment with either 0.2mg/kg agalsidase alppha (10 males, 8 females) or beta (8 males, 5 females) or 1.0mg/kg agalsidase beta (10 males, 11 females). Antibodies were detected in 18/28 male patients after 6 months. None of the females developed antibodies. Following 12 months of 0.2mg/kg treatment, urinary GL-3 decreased in antibody negative (AB-) but increased in antibody positive (AB+) patients. Treatment with 1.0mg/kg gave a reduction in urinary GL-3 in both AB- and AB+ patients. Levels of plasma GL-3 and chitotriosidase decreased in all patient groups. Twelve months of 0.2mg/kg treatment did not change renal function or left ventricular mass. Further, no change in renal function was seen following 1.0mg/kg treatment and left ventricular mass decreased in both AB- and AB+ patients. In summary, alpha-Gal A antibodies frequently develop in male Fabry disease patients and interfere with urinary GL-3 excretion. Infusion of a dose of 1.0mg/kg results in a more robust decline in GL-3, less impact, if any of antibodies, stable renal function and reduction of LVMass.

Mutation spectrum of 122 hemophilia A families from Taiwanese population by LD-PCR, DHPLC, multiplex PCR and evaluating the clinical application of HRM

Background

Hemophilia A represents the most common and severe inherited hemorrhagic disorder. It is caused by mutations in the F8 gene, which leads to a deficiency or dysfunctional factor VIII protein, an essential cofactor in the factor X activation complex.

Methods

We used long-distance polymerase chain reaction and denaturing high performance liquid chromatography for mutation scanning of the F8 gene. We designed the competitive multiplex PCR to identify the carrier with exonal deletions. In order to facilitate throughput and minimize the cost of mutation scanning, we also evaluated a new mutation scanning technique, high resolution melting analysis (HRM), as an alternative screening method.

Results

We presented the results of detailed screening of 122 Taiwanese families with hemophilia A and reported twenty-nine novel mutations. There was one family identified with whole exons deletion, and the carriers were successfully recognized by multiplex PCR. By HRM, the different melting curve patterns were easily identified in 25 out of 28 cases (89%) and 15 out of 15 (100%) carriers. The sensitivity was 93 % (40/43). The overall mutation detection rate of hemophilia A was 100% in this study.

Conclusion

We proposed a diagnostic strategy for hemophilia A genetic diagnosis. We consider HRM as a powerful screening tool that would provide us with a more cost-effective protocol for hemophilia A mutation identification.

Correlation between clinical phenotypes and X-inactivation patterns in six female carriers with heterozygote vasopressin type 2 receptor gene mutations

About 90% of patients with congenital nephrogenic diabetes insipidus (NDI) have vasopressin type 2 receptor (V2R) gene mutations that are inherited in an X-linked recessive manner. Although most female carriers are asymptomatic, some female carriers show polydipsia and polyuria. The reason why female carriers show NDI symptoms is explained by skewed X-inactivation. We studied X-inactivation patterns of six female carriers with heterozygote V2R gene mutations. The X-inactivation pattern in peripheral blood leukocytes was examined using methylation analysis of the polymorphic CAG repeat in the androgen receptor gene. Two asymptomatic female carriers showed random X-inactivation (61.9% and 60.7%). Skewed X-inactivation patterns (71.6%, 79.4%, and 91.2%) occurring preferentially to normal X alleles were recognized in three female carriers who showed clinical NDI symptoms. However, in one female carrier who showed clinical NDI symptoms, random X-inactivation (55.4%) was recognized. In conclusion, the clinical NDI phenotypes may correlate with the X-inactivation patterns in female carriers with heterozygote V2R gene mutations. However, in some female carriers, we cannot predict the clinical phenotypes by the evaluation of the X-inactivation patterns in peripheral blood leukocytes, because X-inactivation ratios within an individual are sometimes different between tissues.

X inactivation, female mosaicism, and sex differences in renal diseases

A good deal of sex differences in kidney disease is attributable to sex differences in the function of genes on the X chromosome. Males are uniquely vulnerable to mutations in their single copy of X-linked genes, whereas females are often mosaic, having a mixture of cells expressing different sets of X-linked genes. This cellular mosaicism created by X inactivation in females is most often advantageous, protecting carriers of X-linked mutations from the severe clinical manifestations seen in males. Even subtle differences in expression of many of the 1100 X-linked genes may contribute to sex differences in the clinical expression of renal diseases.

Urinary globotriaosylceramide excretion correlates with the genotype in children and adults with Fabry disease

Fabry disease is a complex, multisystemic and clinically heterogeneous disease, in which the urinary excretion of globotriaosylceramide (Gb3), the principal substrate of the deficient enzyme, alpha-galactosidase A, is more prominent than the increased concentrations of the lipid in the plasma of affected hemizygotes and heterozygotes. We have developed and validated a simultaneous analysis of Gb3 and creatinine in a 2.6-min run using filter paper discs saturated with urine and analyzed by LC-MS/MS. Using this method, we studied the relationship between urinary levels of total Gb3/creatinine excretion and four types of mutations in the GLA gene (missense, nonsense, frameshift, and splice-site defects) in 32 children and 78 adult patients with Fabry disease. Forty-one patients were treated by enzyme replacement therapy and 69 were untreated. Our results show that the mean recoveries of Gb3 and creatinine from the urine filter paper standards were 91% and 97%, respectively, with precision, reproducibility, and linearity within acceptable ranges. Statistical analysis using the independent variables of sex, age, types of mutations and treatment showed that the mutation factor has a statistically significant impact on urinary Gb3 excretion (p = 0.0007). This means that the levels of urinary excretion of Gb3/creatinine in children and adults with Fabry disease are directly related to the types of mutations. The same correlation was found for the sex (p < 0.0001) and treatment (p = 0.0011). In conclusion, we studied 35 mutations in 110 children and adults with Fabry disease and found a significant correlation between the types of mutations and total Gb3 excretion in Fabry patients.

Treatment of Fabry disease: outcome of a comparative trial with agalsidase alfa or beta at a dose of 0.2 mg/kg

Background

Two different enzyme preparations, agalsidase alfa (Replagal^TM, Shire) and beta (Fabrazyme^TM, Genzyme), are registered for treatment of Fabry disease. We compared the efficacy of and tolerability towards the two agalsidase preparations administered at identical protein dose in a randomized controlled open label trial.

Methodology/Principal Findings

Thirty-four Fabry disease patients were treated with either agalsidase alfa or agalsidase beta at equal dose of 0.2 mg/kg biweekly. Primary endpoint was reduction in left ventricular mass after 12 and 24 months of treatment. Other endpoints included occurrence of treatment failure (defined as progression of cardiac, renal or cerebral disease), glomerular filtration rate, pain, anti-agalsidase antibodies, and globotriaosylceramide levels in plasma and urine. After 12 and 24 months of treatment no reduction in left ventricular mass was seen, which was not different between the two treatment groups. Also, no differences in glomerular filtration rate, pain and decline in globotriaosylceramide levels were found. Antibodies developed only in males (4/8 in the agalsidase alfa group and 6/8 in the agalsidase beta group). Treatment failure within 24 months of therapy was seen in 8/34 patients: 6 male patients (3 in each treatment group) and 2 female patients (both agalsidase alfa). The occurrence of treatment failures did not differ between the two treatment groups; χ² = 0.38 p = 0.54.

Conclusion

Our study revealed no difference in reduction of left ventricular mass or other disease parameters after 12 and 24 months of treatment with either agalsidase alfa or beta at a dose of 0.2 mg/kg biweekly. Treatment failure occurred frequently in both groups and seems related to age and severe pre-treatment disease.

Trial Registration

International Standard Randomized Clinical Trial ISRCTN45178534

Maladie de Fabry: propositions d'ungroupe d'experts français concernant le diagnostic, le traitement et le suivi des patients

Fabry disease is a rare and under-recognized disease associated with an altered X-linked gene controlling hydrolase alpha-galactosidase A activity. This mutation impairs the glycosphingolipid metabolism. A multisystemic disease with a highly variable clinical presentation, its principal symptom is acroparesthesia. Manifestations of Fabry disease occur mostly in hemizygous males but also in heterozygous females. Before enzyme replacement therapy was available, life expectancy was about 50 years in men and 70 years in women. Early diagnosis is essential to prevent irreversible organ damage. Diagnosis is based on an assay of alpha-galactosidase A activity in male patients and on genetic analysis in female patients. Prognosis is related principally to three complications: involvement of the central nervous system, kidneys, and heart. Management of Fabry patients should in all cases combine symptomatic therapy and regular clinical, laboratory and morphological follow-up by specialists in genetic metabolic diseases. Enzyme replacement therapy should be considered in all adult male patients and should probably begin early. In adult heterozygous female patients and in children, this treatment should be considered only for patients with severe pain, organ damage, or central nervous system, kidney, or heart involvement. After a proband is identified, a genealogical tree should be used to identify other affected members of the family.

Structure-function relationships in alpha-galactosidase A

With recent interest in the molecular mechanisms responsible for Fabry disease, the number of known mutations in the GLA gene which encodes alpha-galactosidase A has expanded considerably. Combining a large database of Fabry disease-causing mutations with the recently determined crystal structure of human alpha-galactosidase A allows for a new understanding of the atomic defects in the protein responsible for Fabry disease. We have conducted a systematic survey of the known Fabry disease-causing mutations and analyzed the mutations in the context of the alpha-galactosidase A structure. We have applied quantitative methods for identifying the plausible effect of each mutation on the alpha-galactosidase A protein. We present the analysis of 331 different defects in the GLA gene leading to non-native proteins in patients with Fabry disease. These mutations include 278 missense mutations, 49 nonsense mutations, and four single amino acid deletions.

CONCLUSION

Over half of the residues in the protein have been found to have changes in patients with Fabry disease. Most of these genetic mutations lead to disruption of the hydrophobic core of the protein, thus Fabry disease is primarily a disease of protein-folding. Further understanding of alpha-galactosidase A, one of the best studied members of the lysosomal storage disease family, will lead to increased understanding of other lysosomal storage diseases and other protein-folding diseases.

The Dutch Fabry cohort: diversity of clinical manifestations and Gb3 levels

BACKGROUND

Fabry disease (OMIM 301500) is an X-linked lysosomal storage disorder with characteristic vascular, renal, cardiac and cerebral complications. Globotriaosylceramide (Gb(3)) accumulates in Fabry patients as a result of alpha-galactosidase A deficiency. The phenotypic variability is high, but the relationship between clinical symptoms in individual Fabry patients has not been uniformly documented. Also, the relation between the most prominent biochemical abnormalities, elevated Gb(3) levels in plasma and urine, and clinical symptoms is not firmly established.

METHODS

Clinical and biochemical characteristics of 96 (25 deceased) Dutch Fabry patients were collected retrospectively and before the initiation of enzyme therapy.

RESULTS

Clinical assessment revealed that median life expectancy was 57 years for male and 72 years for female patients. Cerebral complications, acroparaesthesias and gastrointestinal complications, but not cardiac and auditory complications, were all seen more frequently in male than female patients. Glomerular filtration rate (GFR) was highly variable in male patients, including 2 patients with GFR < 30 ml/min, but median GFR did not differ between males and females (103 and 101 ml/min, respectively). Hyperfiltration was more frequently observed in the female patient group. Microalbuminuria was present in 60% of males and 45% of females. No specific pattern of combined symptoms existed except for a relationship between left ventricular hypertrophy (LVH) and cerebral complications (males 36%, females 32%), or proteinuria (males 35%, females 31%). Gb(3) was found to be more elevated in plasma samples from male (n = 26; median 6.27 micromol/L (1.39-9.74)) than female Fabry patients (n = 37; median 2.16 (0.77-4.18)). This was also observed for urinary Gb(3): males (n = 22) median 1851 nmol/24 h (40-3724); females (n = 29) median 672 (86-2052). Plasma and urinary Gb(3) levels correlated with each other in both males (r = 0.4, p = 0.05) and females (r = 0.4, p = 0.03), but no correlation between elevated Gb(3) levels and clinical symptoms could be detected.

CONCLUSION

Analysis of the characteristics of the Dutch Fabry cohort has revealed that a limited relationship between various disease manifestations exists and that individual symptoms do not correlate with elevated urinary or plasma Gb(3) levels, limiting their value as surrogate disease markers.

Neurological manifestations in Fabry's disease

Fabry's disease is an X-linked lysosomal storage disorder caused by a defect in the gene that encodes the lysosomal enzyme alpha-galactosidase A. Symptoms arise because of accumulation of globotriaosylceramide in multiple organs, resulting in severely reduced quality of life and premature death. Neurological symptoms, such as burning sensations (occasionally accompanied by acroparesthesia) and stroke, are among the first to appear, and occur in both male and female patients. A delay in establishing the diagnosis of Fabry's disease can cause unnecessary problems, especially now that enzyme replacement treatment is available to prevent irreversible organ damage. Females with Fabry's disease who present with pain have often been ignored and misdiagnosed because of the disorder's X-linked inheritance. This Review will stress the importance of recognizing neurological symptoms for the diagnosis of Fabry's disease. The possible pathophysiological background will also be discussed.

Manifestations of Fabry disease in placental tissue

Fabry disease is an X-linked lysosomal storage disorder caused by deficiency of the lysosomal enzyme alpha-galactosidase A. Manifestations of the disease in placental tissue have been reported only twice. We report for the first time on the biochemical, histological and genetic features of two cases: placenta A derived from a mother heterozygous for Fabry disease who gave birth to a hemizygous son, and placenta B obtained from a healthy mother who carried a heterozygous daughter. Biopsies of placentae A, B and of four healthy controls were taken directly after birth. Assessment of alpha-galactosidase A (alpha-Gal) activity was performed both in fetal leukocytes (derived from umbilical cord blood) and in the biopsy specimens. The tissue was further examined by electron microscopy, immunohistochemistry and biochemical analysis for the presence of storage material (ceramide trihexoside (CTH)). In placenta A, characteristic zebra bodies reflecting accumulated storage material were seen in all biopsies evaluated. CTH values were markedly elevated as compared to the controls and alpha-Gal activity in both fetal leukocytes and placental tissue was very low. Placenta B showed no storage material at all. CTH values were within the control range. alpha-Gal activity ranged from intermediate to near normal; enzyme activity in fetal leukocytes was significantly decreased. As placental tissue is mainly derived from fetal cells, we may conclude that, in a boy suffering from Fabry disease, extensive storage of CTH is already present at birth. As complications develop only around the age of 10 years, it may be not the CTH itself but secondary processes that cause cellular and organ damage.

Fabry disease: an ultrastructural comparative study of skin in hemizygous and heterozygous patients

Fabry disease is a rare X-linked lysosomal storage disorder due to alpha galactosidase A deficiency, better known after the advent of a promising treatment, a periodical enzyme replacement. As other hereditary X-linked disorders, females have historically been considered non-affected carriers, although they are, actually, clinically and pathologically affected to a variable degree. Some women are asymptomatic, but the majority present milder forms of the disease and later onset. This wide range of disease expression is supposed to be related to the levels of enzymatic activity, probably in accordance with a skewing of X inactivation. Lysosomal deposits of ceramide trihexoside have been repeatedly documented in a wide range of tissues, including those found in angiokeratoma, the characteristic cutaneous lesion which allowed the definition of Fabry disease. The aim of this study was to investigate whether there was any difference in the amount of dermal lysosomal storage in males and females, thus accounting for the difference in clinical severity of both groups. For that purpose, with electron microscopy and quantitative methods, we studied the extent of lysosomal deposits in dermal fibroblasts of normal-appearing skin in six females and nine men, enzymatically and genetically proven as to have Fabry disease, and results were compared. Our results indicate a statistically significant difference between the two groups regarding both the percentage of dermal fibroblasts bearing stored material, and the storage surface occupied in 100 fibroblasts per case. We suggest that periodical ultrastructural examination of normal-appearing skin could be an indicator of the efficacy of enzyme replacement therapy and could help to evaluate results.