Disease manifestations and X inactivation in heterozygous females with Fabry disease

AIM: Fabry disease is an X-linked lysosomal storage disorder characterized by an accumulation of neutral glycosphingolipids in multiple organ systems caused by alpha-galactosidase A deficiency due to mutations in the GLA gene. The majority of heterozygous females show the characteristic signs and symptoms of the disease, and some of them are severely affected. The current hypothesis for the occurrence of disease manifestations in females is skewed X inactivation favouring the mutant GLA allele. METHOD: We analyzed the patterns of X inactivation in the leukocytes of 28 biochemically and genetically characterized symptomatic Fabry disease heterozygotes and their correlation with clinical and biochemical disease expression. RESULTS: X inactivation patterns in symptomatic females who are heterozygous for Fabry disease did not differ from those of female controls of the same age (p = 0.669). Thirteen (46%) of the 28 females with Fabry disease showed random X inactivation, ten (36%) moderate skewing, and five (18%) highly skewed X inactivation. Segregation analysis was performed in the families of six females who had highly or moderately skewed X inactivation. In four of these females, skewing favoured the wild-type GLA allele and in the other two skewing favoured the mutant allele. Patterns of X inactivation or the extent of skewing were not related to the severity of clinical manifestations or to residual enzyme activity. CONCLUSION: In this study we provide evidence that heterozygous females with Fabry disease show random X inactivation. Our data do not support the hypothesis that the occurrence and severity of disease manifestations in the majority of Fabry heterozygotes are related to skewed X inactivation.     

Skewed X inactivation in healthy individuals and in different diseases

In female mammalian cells, one of the two X chromosomes is inactivated in early embryonic life. Females are mosaics for two cell populations, one with the maternal and one with the paternal X as the active chromosome. Skewed X inactivation is arbitrarily defined, often as a pattern where 80% or more of the cells show a preferential inactivation of one X chromosome. Inactivation is presumed to be permanent for all descendants of a cell; however, after about 55 years of age, the frequency of skewed X inactivation in peripheral blood cells increases, probably through selection. Unfavourable skewing of X inactivation, where the X chromosome carrying a mutant allele is the predominantly active X, has been found in affected female carriers of several X-linked disorders; however, for many X-linked disorders, a consistent relationship between the pattern of X inactivation and clinical phenotype has been difficult to demonstrate. One reason for this may be that peripheral blood cells are not a representative or relevant tissue in many disorders. In some severe X-linked disorders, post-inactivation selection takes place against the X chromosome carrying the mutant allele, leading to a completely skewed X-inactivation pattern. Skewed X inactivation has also been reported in young females with breast cancer, and may indicate an effect of X-linked genes on the development of this condition.
Conclusion: The process of X inactivation and the resultant degree of skewing is clearly important for the expression of genetic diseases. It is also important to consider, however, that under normal conditions the frequency of skewed X inactivation increases with age in peripheral blood cells. Analysis of the expression of a large proportion of the genes on the X chromosome has revealed that X-chromosome inactivation is more heterogeneous than previously thought.     

Skewed X inactivation in healthy individuals and in different diseases

In female mammalian cells, one of the two X chromosomes is inactivated in early embryonic life. Females are mosaics for two cell populations, one with the maternal and one with the paternal X as the active chromosome. Skewed X inactivation is arbitrarily defined, often as a pattern where 80% or more of the cells show a preferential inactivation of one X chromosome. Inactivation is presumed to be permanent for all descendants of a cell; however, after about 55 years of age, the frequency of skewed X inactivation in peripheral blood cells increases, probably through selection. Unfavourable skewing of X inactivation, where the X chromosome carrying a mutant allele is the predominantly active X, has been found in affected female carriers of several X-linked disorders; however, for many X-linked disorders, a consistent relationship between the pattern of X inactivation and clinical phenotype has been difficult to demonstrate. One reason for this may be that peripheral blood cells are not a representative or relevant tissue in many disorders. In some severe X-linked disorders, post-inactivation selection takes place against the X chromosome carrying the mutant allele, leading to a completely skewed X-inactivation pattern. Skewed X inactivation has also been reported in young females with breast cancer, and may indicate an effect of X-linked genes on the development of this condition.Conclusion: The process of X inactivation and the resultant degree of skewing is clearly important for the expression of genetic diseases. It is also important to consider, however, that under normal conditions the frequency of skewed X inactivation increases with age in peripheral blood cells. Analysis of the expression of a large proportion of the genes on the X chromosome has revealed that X-chromosome inactivation is more heterogeneous than previously thought.     

X-chromosome inactivation: role in skin disease expression

The occurrence of X inactivation in mammals has the consequence that all women are functional mosaics. In X-linked skin disorders, Lyonization usually gives rise to a mosaic pattern, as manifest by the appearance of the lines of Blaschko. This arrangement of lesions is observed in male-lethal X-linked traits, such as incontinentia pigmenti, focal dermal hypoplasia, Conradi-Hünermann-Happle syndrome, oral-facial-digital syndrome type 1 and MIDAS (microphthalmia, dermal aplasia and sclerocornea) syndrome, as well as in various X-linked non-lethal phenotypes, such as hypohidrotic ectodermal dysplasia of Christ-Siemens-Touraine, IFAP (ichthyosis follicularis-alopecia-photophobia) syndrome and X-linked dyskeratosis congenita. Analogous X-inactivation patterns have been documented in human bones, teeth, eyes and, possibly, the brain. Patterns that are distinct from the lines of Blaschko are also seen, such as the lateralization observed in CHILD (congenital hemidysplasia with ichthyosiform nevus and limb defects) syndrome, and the chequerboard pattern seen in women heterozygous for X-linked congenital hypertrichosis. Exceptional cases of either severe or absent involvement in a woman heterozygous for an X-linked trait can be explained by skewing of X inactivation. Some X-linked skin disorders are caused by genes that escape inactivation, which is why heterozygous female 'carriers' of these disorders do not show mosaicism. A well-known example is X-linked recessive ichthyosis due to steroid sulphatase deficiency, the locus for which is situated at the tip of the short arm of the X chromosome and does not undergo Lyonization. On the other hand, in the case of Fabry disease, the gene encoding alpha-galactosidase A is subject to inactivation. Remarkably, however, the skin lesions of women do not show a mosaic pattern.Conclusion: In the various X-linked skin disorders, affected women show quite dissimilar degrees of involvement and forms of manifestation because X inactivation may give rise to different patterns of functional mosaicism. Paradoxically, no such pattern is observed in women with Fabry disease. Like many X-linked diseases, Fabry disease should neither be called recessive nor dominant, because these dichotomous terms are obscured by the mechanism of X inactivation.     

X-chromosome inactivation and human genetic disease

The inactivation of one X-chromosome in females in early development is the process by which the effective dosage of X-linked genes is equalized between XX females and XY males. The mechanism that brings this about is the subject of intense research. The X-linked gene Xist is a key player, which is necessary but not sufficient for the initiation of X-inactivation. It codes for an untranslated RNA that coats the inactive X-chromosome, which takes on properties characteristic of heterochromatin, but how this change in chromatin is brought about remains unknown. Because of X-inactivation, females heterozygous for X-linked genes are mixtures of two types of cells and show a variable phenotype. The proportion s of the two types of cells can depart from equality due to cell selection either at the tissue or whole organism level. In rare cases, changes in the Xist gene can cause skewing of X-inactivation. A few genes escape from X-inactivation either wholly or partially.
Conclusion : X-chromosome inactivation is a physiological mechanism that equalizes gene-dosage effects on the sex chromosomes. The occurrence of this normal process affects the phenotype seen in females carrying X-linked mutant genes or chromosome anomalies.     

Genotype and phenotype in Fabry disease: analysis of the Fabry Outcome Survey

Aim: Mutations of the gene ( GLA ) encoding α-galactosidase A are implicated in Fabry disease, a progressive, X-chromosomal inherited lysosomal storage disorder. FOS – the Fabry Outcome Survey – was established as a long-term surveillance study to describe the natural course of Fabry disease and its response to enzyme replacement therapy in a large cohort of European patients. Clinical phenotype, age of onset and course of Fabry disease are very variable, even within the same family, which makes it difficult to define a genotype–phenotype relationship by analysing individual patients. The FOS database contains detailed medical information on a large cohort of patients and thus has the potential to provide important information to address this question. Methods: At the time of analysis, information on 545 patients belonging to 157 families from nine European countries had been entered into the FOS database. A GLA mutation has been reported in 365 individuals (65% and 68% of all males and females, respectively) in FOS. These data were used to analyse the relationship between genotype and phenotype in Fabry disease. Results: A highly significant positive correlation was found between the age at entry into FOS and the FOS Severity Index in male patients with GLA missense mutations ( p <0.001) as well as in those carrying other types of mutations ( p <0.001). A positive correlation was also found between the age at entry into FOS and the number of affected organs in male patients with missense mutations, irrespective of whether the change in the amino acid side chain predicted in the α-galactosidase A protein was classified as a conservative or non-conservative change.
Conclusion: The data presented here suggest that there is a correlation between genotype and clinical severity.     

Increased carotid intima–media thickness in the absence of atherosclerotic plaques in an adult population with Fabry disease

Aim: Fabry disease is considered primarily as a progressive small vessel disease, with ischaemic degenerative lesions involving the kidneys, brain and heart. Macrovascular involvement in male patients includes an accelerated wall hypertrophy of the radial artery and a thickening of the intima–media of the common carotid artery. The aim of this study is to evaluate the prevalence and severity of carotid artery atherosclerosis in hemizygous and heterozygous patients with Fabry disease, compared with a matched control population.
Methods: The common carotid artery intima–media thickness (IMT) of 53 patients with Fabry disease (24 men, 29 women) was measured by high-definition ultrasonography, and the presence or absence of atherosclerotic plaques reported. Results were compared with those of 120 age-matched healthy individuals (83 men, 37 women).
Results: The common carotid artery IMT was increased to the same extent in male and female patients with Fabry disease (706±211 µm and 749±395 µm, respectively) compared with that of the control population (614±113 µm). In the Fabry population, IMT did not correlate with either systolic blood pressure or with renal function (plasma creatinine). In the control population, only systolic blood pressure was positively and significantly correlated with IMT. Atherosclerotic plaques in the common carotid artery were not observed in any patient with Fabry disease, whereas 34% of the control population had carotid artery plaques, as evidenced by focal non-homogeneous intima–media thickening greater than 1.2 mm.
Conclusion: This study presents evidence of a major increase in common carotid artery IMT, both in hemizygous and heterozygous patients with Fabry disease, in the absence of focal atherosclerotic plaques. These results suggest that the conduit arteries may be protected from atherosclerosis in Fabry disease.     

Evolution of renal pathology in Fabry disease

Fabry disease is a rare lysosomal storage disorder which results from deficient activity of the enzyme α-galactosidase A. The resultant deposition and progressive accumulation of glycosphingolipids in all types of body tissue leads to severe clinical manifestations involving the heart, CNS and kidney. Renal manifestations are observed relatively early in the course of the disease, and progression to end-stage renal failure is common in hemizygous males in the third to fifth decades of life.
Renal biopsy specimens reveal evidence of diffuse intracytoplasmic glycosphingolipid accumulation, mainly affecting podocytes and epithelial cells of distal tubules, which are strikingly enlarged and vacuolated. On electron microscopy the deposits appear as typical osmiophilic inclusion bodies in the cytoplasm of all kinds of renal cells, and show a characteristic 'onion skin' or 'zebra' appearance. These pathological features are also evident in heterozygous females. Deposits occur before the development of renal impairment. As patients age, the disease progresses in cells throughout the kidney, and is associated with increasing glycosphingolipid accumulation.
Conclusion : The age-related evolution of renal pathology in Fabry disease is closely correlated with progressive intracellular deposition of glycosphingolipid and ultimately leads to end-stage renal failure.     

Genotype and phenotype in Fabry disease: analysis of the Fabry Outcome Survey

AIM: Mutations of the gene (GLA) encoding alpha-galactosidase A are implicated in Fabry disease, a progressive, X-chromosomal inherited lysosomal storage disorder. FOS--the Fabry Outcome Survey - was established as a long-term surveillance study to describe the natural course of Fabry disease and its response to enzyme replacement therapy in a large cohort of European patients. Clinical phenotype, age of onset and course of Fabry disease are very variable, even within the same family, which makes it difficult to define a genotype-phenotype relationship by analysing individual patients. The FOS database contains detailed medical information on a large cohort of patients and thus has the potential to provide important information to address this question. METHODS: At the time of analysis, information on 545 patients belonging to 157 families from nine European countries had been entered into the FOS database. A GLA mutation has been reported in 365 individuals (65% and 68% of all males and females, respectively) in FOS. These data were used to analyse the relationship between genotype and phenotype in Fabry disease. RESULTS: A highly significant positive correlation was found between the age at entry into FOS and the FOS Severity Index in male patients with GLA missense mutations (p < 0.001) as well as in those carrying other types of mutations (p < 0.001). A positive correlation was also found between the age at entry into FOS and the number of affected organs in male patients with missense mutations, irrespective of whether the change in the amino acid side chain predicted in the alpha-galactosidase A protein was classified as a conservative or non-conservative change. CONCLUSION: The data presented here suggest that there is a correlation between genotype and clinical severity.     

X-chromosome inactivation and human genetic disease

The inactivation of one X-chromosome in females in early development is the process by which the effective dosage of X-linked genes is equalized between XX females and XY males. The mechanism that brings this about is the subject of intense research. The X-linked gene Xist is a key player, which is necessary but not sufficient for the initiation of X-inactivation. It codes for an untranslated RNA that coats the inactive X-chromosome, which takes on properties characteristic of heterochromatin, but how this change in chromatin is brought about remains unknown. Because of X-inactivation, females heterozygous for X-linked genes are mixtures of two types of cells and show a variable phenotype. The proportions of the two types of cells can depart from equality due to cell selection either at the tissue or whole organism level. In rare cases, changes in the Xist gene can cause skewing of X-inactivation. A few genes escape from X-inactivation either wholly or partially. CONCLUSION: X-chromosome inactivation is a physiological mechanism that equalizes gene-dosage effects on the sex chromosomes. The occurrence of this normal process affects the phenotype seen in females carrying X-linked mutant genes or chromosome anomalies.     

Electrocardiographic signs of hypertrophy in Fabry disease-associated hypertrophic cardiomyopathy

Aims : Fabry disease results from deficient activity of the lysosomal enzyme α-galactosidase A. Progressive accumulation of the major substrates leads, in both men and women, to progressive hypertrophic cardiomyopathy. We aimed to evaluate the utility of different electrocardiographic (ECG) parameters for assessing the degree and severity of hypertrophic cardiomyopathy in patients with Fabry disease. Methods : A total of 166 ECGs of 94 hemi- and heterozygous patients with Fabry disease were analysed and compared with echocardiographic-estimated left ventricular mass (LVM). Results : There was a significant ( p > 0.0001) correlation between QRS duration (R²= 0.59), 12-lead amplitude/duration product (R²= 0.61), Sokolow-Lyon voltage/duration product (R²= 0.52) and LVM. Analysis of receiver operating characteristics revealed that the 12-lead amplitude/duration product had the highest sensitivity-specificity relationship ( p > 0.01 compared with the Cornell index).
Conclusion : In general, ECG signs of left ventricular hypertrophy correlated well with LVM as revealed by echocardiography. Of the parameters studied, the 12-lead amplitude/duration product was the most successful at describing the severity of cardiac involvement in Fabry disease. These data suggest that ECG parameters have potential for use as a simple and cost-effective means of screening for hypertrophic cardiomyopathy in patients with Fabry disease.     

法布里病患儿临床特点及酶替代治疗四例初探

目的分析法布里病患儿的临床特点及使用酶替代药物治疗基本情况。方法对2014年1月至2020年7月间浙江大学医学院附属儿童医院确诊的4例法布里病患儿的临床资料、实验室检查、基因变异及治疗进行回顾性分析。临床观察其酶替代药物阿加糖酶β治疗的效果。结果 4例患儿(男2例、女2例)年龄12.4(6.0~16.8)岁,临床表现各异,其中肢端疼痛1例、少汗2例、尿崩1例,均有左心室肥厚和尿检异常,但均未发现典型皮疹及听力异常。4例患儿均结合临床症状、体征、家族史,通过α-半乳糖苷酶A酶活性、基因检测结果明确诊断。共检出3个GLA基因错义变异 c.424T>C(p.C142R)、c.335G>A(p.R112H)和c.644A>G(p.N215S)。其中前2个变异为经典型法布里病患者变异位点,后者多表现为迟发型但亦有经典型的报道。例1使用阿加糖酶β用量为每次1 mg/kg静脉泵注,每2周用药1次。患儿诉用药后疼痛强度有缓解,少汗症状得到改善。患儿在最初的2个月输注阿加糖酶β过程中未发生严重不良反应,在输注阿加糖酶β 3次后24 h尿蛋白升至1 015.6 mg,未予处理,1周后复查降至正常。结论法布里病在儿童期临床表现多样,需要多学科联合协同诊断并探讨酶替代治疗的时机,阿加糖酶β治疗患儿短期严重不良反应少见。     

Severe X-linked chronic granulomatous disease in two unrelated females

Chronic granulomatous disease (CGD) is a rare primary immunodeficiency caused by mutations of one of the subunits of phagocyte reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase leading to decreased or complete absence of neutrophil oxidative burst. We report the clinical and laboratory findings in two young unrelated females 14 and 9 years of age and natives of Tahiti and Reunion Islands, respectively, with severe X-linked granulomatous disease. In both cases, the infectious pattern was unusual, with convergent symptoms suggesting underlying mycobacterial infection. Functional analysis revealed low residual NADPH oxidase activity with about 5–10% of normal neutrophil population. De novo null mutations affecting the CYBB gene that encodes the gp91 protein were found in both cases in the heterozygous state (in patient 1, p.Arg130X in exon 5, and in patient 2, a novel insertion in exon 6, c.632_633insCATC). Methylation analysis confirmed that phenotype expression was linked to skewed X inactivation and showed that the de novo mutation arose on the maternally inherited chromosome in one case and on the paternally inherited chromosome in the other case. In conclusion, X-linked CGD carriers could therefore be at risk for severe infectious diseases depending on the skewed X inactivation pattern and the infectious context.     

The Mainz Severity Score Index (MSSI): development and validation of a system for scoring the signs and symptoms of Fabry disease

Fabry disease is a rare lysosomal storage disorder caused by the deficient activity of the lysosomal enzyme α-galactosidase A. The resultant storage of undegraded glycolipids leads to the progressive development of potentially life-threatening manifestations affecting multiple organ systems in the body. This paper describes the development of the Mainz Severity Score Index (MSSI), a scoring system for patients with Fabry disease.
Conclusion: The MSSI score has been proven to be representative in patients with 'classic' Fabry disease and may be useful for monitoring clinical improvement in patients receiving enzyme replacement therapy.     

Effects of enzyme replacement therapy with agalsidase alfa on glomerular filtration rate in patients with Fabry disease: preliminary data

Progressive deposition of globotriaosylceramide results in severe complications involving the kidney, heart and brain in both hemizygous male and heterozygous female patients with Fabry disease. Analysis of renal data from FOS - the Fabry Outcome Survey - suggests that enzyme replacement therapy with agalsidase alfa can significantly improve renal function in patients with Fabry disease, at least in those with a mild decrease in glomerular filtration rate, and may also be able to slow down the natural decline in renal function in patients with a moderate reduction in glomerular filtration rate.
Conclusion : Initial results from the large cohort of patients within FOS indicate that treatment with agalsidase alfa has beneficial effects on kidney function in patients with Fabry disease.     

Isolated cardiac manifestations in Fabry disease: the UK experience

Cardiac abnormalities are common in patients with Fabry disease, and may be the only clinical manifestation of the disease in some patients. At St George's Hospital Medical School, a national referral centre for hypertrophic cardiomyopathy in the UK, a study of 153 consecutively referred male patients revealed that 4% had Fabry disease. This increased to 6% in patients over 40 years of age. All these patients had electrocardiographic (ECG) abnormalities, most of which were consistent with those found in patients with classic Fabry disease: left ventricular hypertrophy, repolarization abnormalities and a prolonged QRS complex. A study of heterozygote females with Fabry disease also showed ECG and echocardiographic abnormalities in most patients.
Conclusions : Fabry disease should be considered in the differential diagnosis of otherwise unexplained cardiac disease.     

Evolution of renal pathology in Fabry disease

Fabry disease is a rare lysosomal storage disorder which results from deficient activity of the enzyme alpha-galactosidase A. The resultant deposition and progressive accumulation of glycosphingolipids in all types of body tissue leads to severe clinical manifestations involving the heart, CNS and kidney. Renal manifestations are observed relatively early in the course of the disease, and progression to end-stage renal failure is common in hemizygous males in the third to fifth decades of life. Renal biopsy specimens reveal evidence of diffuse intracytoplasmic glycosphingolipid accumulation, mainly affecting podocytes and epithelial cells of distal tubules, which are strikingly enlarged and vacuolated. On electron microscopy the deposits appear as typical osmiophilic inclusion bodies in the cytoplasm of all kinds of renal cells, and show a characteristic 'onion skin' or 'zebra' appearance. These pathological features are also evident in heterozygous females. Deposits occur before the development of renal impairment. As patients age, the disease progresses in cells throughout the kidney, and is associated with increasing glycosphingolipid accumulation. CONCLUSION: The age-related evolution of renal pathology in Fabry disease is closely correlated with progressive intracellular deposition of glycosphingolipid and ultimately leads to end-stage renal failure.     

Natural history of the cerebrovascular complications of Fabry disease

Fabry disease is a rare, X-linked lysosomal storage disease caused by an inborn deficiency of α-galactosidase A, which results in progressive accumulation of globotriaosylceramide in a range of cells and tissues. Neurological symptoms of Fabry disease, including peripheral neuropathy and cerebrovascular events, are among the most significant clinical aspects. In this paper we present the natural history and mechanisms involved in the cerebrovascular complications of Fabry disease using data reported in FOS – the Fabry Outcome Survey – and other registries and clinical studies. We discuss ways in which these manifestations can be modified by intervention, including both general measures for cerebrovascular disease and enzyme replacement therapy.
Conclusion: Data from FOS have provided important insights into the natural history of the cerebrovascular complications of Fabry disease. Furthermore, the database has demonstrated that significant renal or cardiac disease often co-exists with cerebrovascular disease, and may predispose patients with Fabry disease to neurological disability and stroke.     

Fabry disease and the heart: an overview of the natural history and the effect of enzyme replacement therapy

Fabry disease is a genetic disorder caused by the deficiency of α-galactosidase A, resulting in the lysosomal accumulation of glycosphingolipids. Fabry disease may result in cardiac, cerebral and renal complications. Cardiac abnormalities in patients with Fabry disease were first described in the 1960s. In the 1990s a form of Fabry disease confined to the heart was reported; however, this variant is extremely rare and a more appropriate concept is of cardiac predominance of the disease in some patients. Up to 60% of males with classic Fabry disease have cardiac abnormalities, including left ventricular hypertrophy, valvular dysfunction and conduction abnormalities. Recent data suggest that left ventricular mass and systolic function in patients with Fabry disease improve after 12 months of enzyme replacement therapy (ERT); however, many of the patients studied are relatively young and have mild cardiac abnormalities, suggesting that more research into the efficacy of ERT in older patients is necessary.
Conclusion: Cardiac manifestations are common in patients with Fabry disease and are not confined to a 'cardiac variant' of the disease.     

Head-impulse testing in Fabry disease - vestibular function in male and female patients

Aim : To study the prevalence of peripheral vestibular deficit in male and female patients with Fabry disease and to assess the effect of enzyme replacement therapy (ERT) on peripheral vestibular function using quantitative head-impulse testing. Methods : Using dual search-coils the vestibulo-ocular reflex during rapid rotational head thrusts to both sides was recorded in 21 patients (13 male, 8 female) with Fabry disease prior to ERT initiation. ERT consisted of infusions of gene-activated human α-galactosidase A (agalsidase alfa; Replagal™) every 2 weeks at doses of 0.2mg/kg. Eight patients were tested again approximately 6 and 12 months after the initiation of ERT. Results : At baseline examination, 15 of the patients with Fabry disease (71%; 11 males, 4 females) showed reduced peripheral vestibular function. The deficit was unilateral in nine patients (3 females) and bilateral in six patients (1 female). The severity of the vestibular deficit was not significantly different between male and female patients. After 12 months of ERT, the average vestibular deficit on the weaker side tended to improve; however, the change was not significant ( p = 0.10).
Conclusion : Fabry disease affects peripheral vestibular function in both male and female patients. Females seem to be affected less frequently than males, but, on average, vestibular deficits are not different between the two groups. To confirm or reject the tendency for vestibular improvement during ERT, more patients need to be tested and longer follow-up periods are required.