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 α-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.     

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.     

Steroid-resistant nephrotic syndrome associated with steroid sulfatase deficiency—x-linked recessive ichthyosis: a case report and review of literature

Nephrotic syndrome associated with X-linked recessive ichthyosis due to steroid sulfatase deficiency has rarely been reported in English literature. We describe a 4 and a half-year-old boy presenting with steroid-resistant nephrotic syndrome (SRNS) with an underlying ichthyotic skin present since birth. Renal biopsy revealed minimal change disease. As many of the male members of the family also showed similar skin manifestations, genetic analysis was done on the patient, which revealed deletion of the steroid sulfatase (STS) gene spanning both the 3′ as well as the 5′ends. The patient was thus diagnosed with SRNS associated with X-linked recessive ichthyosis. He was started on cyclosporine regimen, and remission was achieved in 5 weeks. We speculate that the deficiency of STS resulting in increased cholesterol sulfate accumulation interferes with the integrity of adherens junctions present between glomerular epithelial cells of the slit diaphragm, and this results in proteinuria and nephrotic syndrome. The nephrotic syndrome remitted with a calcineurin inhibitor medication. Conclusion: We suggest that the deficiency of STS is another one in an increasing list of genetic causes of podocytopathy and nephrotic syndrome. Remission of proteinuria in such a case may be achieved with immunosuppressive medication.     

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.     

Duchenne muscular dystrophy in a 4-year-old girl due to heterozygous frame shift deletion of the dystrophin gene and skewed X-inactivation

X-linked recessive diseases affect males, whereas female carriers are generally asymptomatic.We report on a 4-year-old girl who presented with a classical phenotype of Duchenne Muscular Dystrophy (DMD), a severe X-linked recessive type of muscular dystrophy affecting boys in early childhood.A thorough diagnostic work-up revealed that this resulted from a heterozygous out-of frame deletion in the DMD-gene in combination with an X-inactivation ratio of <10:90 in blood leukocytes and muscle.The case exemplifies that a skewed X-inactivation pattern has to be taken into account as mechanism causing clinical symptoms in female carriers of X-linked recessive disorders.     

Absence of testicular steroid sulphatase activity in a boy with recessive X-linked ichthyosis and testicular maldescent

We present a 14-year-old boy with recessive X-linked ichthyosis in whom only one testis could be found. In this apparently normal testis, a lack of activity of the enzyme steroid sulphatase was demonstrated. Several male patients with recessive X-linked ichthyosis have been reported to have testicular diseases, and it is suggested that this may be related to the absence of testicular steroid sulphatase activity.Abbreviations RXLI recessive X-linked ichthyosis - STS steroid sulphatase     

A case of Netherton's syndrome with cerebral infarction

Netherton's syndrome, a rare congenital disease of childhood, is characterized by variable cutaneous erythematous eruptions with different manifestations. A five-year-old boy, who presented with ichthyosis linearis circumflexa, atopic manifestations and pili torti, had spastic hemiparesia due to cerebral infarction. Netherton's syndrome can easily be misdiagnosed as Leiner's disease, generalized psoriasis or nonbullous congenital ichthyosiform erythroderma, especially in the neonatal period, because of its nonspecific clinical and histological features. Pediatricians should consider this syndrome in the differential diagnosis of the generalized erythematous skin disorders of childhood associated with various abnormalities.     

Clinical and molecular spectrum of somatic mosaicism in androgen insensitivity syndrome

We recently found that postzygotic de novo mutations occur at the expected high rate of an X-linked recessive mutation in androgen insensitivity syndrome. The resulting somatic mosaicism can be an important molecular determinant of in vivo androgen action caused by expression of the wild-type androgen receptor (AR). However, the clinical relevance of this previously underestimated genetic condition in androgen insensitivity syndrome has not been investigated in detail as yet. Here, we present the clinical and molecular spectrum of somatic mosaicism considering all five patients with mosaic androgen insensitivity syndrome, whom we have identified since 1993: Patient 1 (predominantly female, clitoromegaly), 172 TTA(Leu)/TGA(Stop); patient 2 (ambiguous), 596 GCC(Ala)/ACC(Thr); patient 3 (ambiguous), 733 CAG(Gln)/ CAT(His); patient 4 (completely female), 774 CGC(Arg)/TGC (Cys); and patient 5 (ambiguous), 866 GTG(Val)/ATG(Met). Serum sex hormone binding globulin response to stanozolol, usually correlating well with in vivo AR function, was inconclusive for assessment of the phenotypes in all tested mosaic individuals. An unexpectedly strong virilization occurred in patients 1, 3, and 5 compared with phenotypes as published with corresponding inherited mutations and compared with the markedly impaired transactivation caused by the mutant ARs in cotransfection experiments. Only the prepubertal virilization of patients 2 and 4 matched appropriately with transactivation studies (patient 4) or the literature (patients 2 and 4). However, partial pubertal virilization in patient 4 caused by increasing serum androgens and subsequent activation of the wild-type AR could not be excluded. We conclude that somatic mosaicism is of particular clinical relevance in androgen insensitivity syndrome. The possibility of functionally relevant expression of the wild-type AR needs to be considered in all mosaic individuals, and treatment should be adjusted accordingly.     

Variable expression in focal dermal hypoplasia. An example of differential X-chromosome inactivation

We encountered three women from three generations of the same family with features of focal dermal hypoplasia (FDH). Two of the patients, the proposita and her mother, demonstrated severe manifestations, including skin, dental, skeletal, and visceral abnormalities. The proposita's grandmother, the first family member affected, had very mild expression, with aplasia cutis congenita and dental caries as the only features expressed. This family illustrates both the marked variability of expression and the proposed X-linked dominant mode of inheritance of FDH. We postulate that early embryologic random inactivation of the X chromosome bearing the mutant gene responsible for FDH is the cause of the variable expression.     

X-linked icthyosis. A sulphatase deficiency.

In 3 pregnant women oestrogen excretion in the urine was very low. The pregnancies were otherwise uncomplicated and the 3 infants, boys, were normal at birth, but later developed ichthyosis of the X-linked inherited type. Histochemically, the placenta in each case showed deficiency in arylsulphatase-type C activity. In all three children the skin showed the same enzyme deficiency. In the skin of 9 other unrelated (adult) patients with proved X-linked inherited ichthyosis vulgaris, arylsulphatase C activity was deficient. Skin from 5 normal adults and 5 normal children showed arylsulphatase C activity to be present. It is concluded that a sulphatase deficiency is a factor in the causation of ichthyosis of the X-linked inherited type.     

Diagnostic problems in a 17-year-old patient with gastrointestinal manifestations of Fabry disease

Fabry disease is a rare X-linked recessive lysosomal storage disorder caused by deficiency of lysosomal enzyme alpha-galactosidase, which leads to accumulation of globotriasylceramides (GL-3) in visceral tissues and vascular endothelium, causing multi-organ failure. We presenta case of Fabry disease in a 17-year-old patient with mainly gastrointestinal manifestations, diagnosed 10 years after the manifestation of first symptoms. Significant and progressive weight loss with abdominal pain and vomiting, leading to cachexia, were observed in early childhood. The patient was investigated for non-inflammatory bowel diseases, Raynaud syndrome, polimyositis, mitochondrial cytopathies, intestinal lypodystrophies and others. The symptoms of intenstinal pseudo-obstruction syndrome were observed and surgical treatment was instituted because of necrosis of the colon. There was progressive cachexia and parenteral nutrition had to be instituted. Finally, plasma alpha-galactosidase was measured, and its deficit confirmed Fabry disease. In conclusion gastrointestinal symptoms in the course of Fabry disease can obscure other characteristic symptoms, may be prodromal and leading. Heart and renal failure may not occur in children. Unexplained abdominal pain and malnutrition may be gastrointestinal manifestations of metabolic disorders.     

Pigmentary abnormalities and mosaicism for chromosomal aberration: association with clinical features similar to hypomelanosis of Ito

Thirteen patients with hypopigmentation of the skin characteristic of hypomelanosis of Ito, and with developmental disabilities or structural malformations, or both, were examined at our center. Eight were found to have abnormal karyotypes in lymphocytes, fibroblasts, or both. No single clinical feature was predictive of chromosome imbalance in this group of patients. Cytogenetic findings included a balanced de novo X-autosome translocation; ring 10; 45,X/46,X,+ring; mosaic del 13q11 (fibroblasts); mosaic triploidy (fibroblasts); mosaic tetrasomy 12p (fibroblasts); mosaic apparently balanced 15;22 translocation (peripheral blood); and mosaic trisomy 18 (peripheral blood). Hypomelanosis of Ito is characterized by swirly hypopigmentation or depigmentation of the skin with or without other malformations. Autosomal dominant, autosomal recessive, and X-linked dominant inheritance have been suggested but not confirmed. Chromosomal aneuploidy has also been reported. We believe that hypomelanosis of Ito is an etiologically heterogeneous physical finding, and recommend karyotyping of multiple tissues of all patients with abnormal cutaneous pigmentation associated with developmental delay or structural malformations.     

The pattern of inheritance of X-linked traits is not dominant or recessive, just X-linked

Our modern concepts of genetic inheritance originated nearly a century ago. Early concepts of dominant and recessive inheritance were developed in insects and were subsequently applied to sex-linked inheritance in mammals. Years of clinical experience, however, suggest that the modern-day rules for X-linked dominant and recessive diseases do not explain why so many female carriers of X-linked 'recessive' disorders have an abnormal phenotype. In a review of 32 X-linked diseases we revealed an unexpectedly high degree of intermediate disease penetrance in females that cannot be explained by existing concepts. We recommend that the terms 'dominant' and recessive' be abandoned and that these disorders be referred to as X-linked. In this review we will present modified rules for X-linked inheritance and propose hypotheses related to the potential mechanisms that may explain differences in disease expression in females.
Conclusion : Past assumptions regarding factors that may affect phenotype in heterozygous females do not capture the extraordinarily variable expressivity of X-linked disorders in females and need to be revisited.     

Spondyloepiphyseal Dysplasia Tarda in Turner Syndrome

ABSTRACT. A girl with short stature is described in whom chromosomal analysis revealed a 45,X/46,XX mosaicism and in whom radiological investigations disclosed the diagnosis of X-linked spondyloepiphyseal dysplasia tarda. This is the first report of the occurrence of X-linked spondyloepiphyseal dysplasia tarda in a child with Turner syndrome.     

The pattern of inheritance of X-linked traits is not dominant or recessive, just X-linked

Our modern concepts of genetic inheritance originated nearly a century ago. Early concepts of dominant and recessive inheritance were developed in insects and were subsequently applied to sex-linked inheritance in mammals. Years of clinical experience, however, suggest that the modern-day rules for X-linked dominant and recessive diseases do not explain why so many female carriers of X-linked 'recessive' disorders have an abnormal phenotype. In a review of 32 X-linked diseases we revealed an unexpectedly high degree of intermediate disease penetrance in females that cannot be explained by existing concepts. We recommend that the terms 'dominant' and recessive' be abandoned and that these disorders be referred to as X-linked. In this review we will present modified rules for X-linked inheritance and propose hypotheses related to the potential mechanisms that may explain differences in disease expression in females.Conclusion: Past assumptions regarding factors that may affect phenotype in heterozygous females do not capture the extraordinarily variable expressivity of X-linked disorders in females and need to be revisited.     

Further delineation of the ichthyosis follicularis,atrichia, and photophobia syndrome

We describe an 18-month-old male infant suffering from the ichthyosis follicularis, atrichia, and photophobia (IFAP) syndrome and further delineate the clinical phenotype. Severe retardation of growth and psychomotor development, chill-like seizures, bronchial asthma, urticaria, a proneness to skin infections and transient nail dystrophy observed in our patient are nonobligatory manifestations of this disorder. Histological examination of the atrichia revealed poorly developed, shortened hair follicles and a complete absence of sebaceous glands. The sex ratio of published cases suggests an X-linked recessive inheritance. The marked clinical variability of the IFAP syndrome might be the expression of a contiguous gene defect.Presented in part at the Fifth International Congress of Paediatric Dermatology, Milan/Italy, 11–15 July, 1989     

Fabry's disease in a black kindred.

In a 16-member black kindred with Fabry's disease, four hemizygous males had plasma alpha-galactosidase levels less than 6% and seven heterozygous females had plasma alpha-galactosidase levels between 10% and 50% of normal. A 16-year-old index male had hypertension with left ventricular hypertrophy, abnormal renal function, tortuous retinal veins, "myelin" inclusions in bone marrow macrophages, and intraepithelial inclusion bodies in the kidney. Scrotal angiectasia developed a year after diagnosis. The three other affected males had left ventricular hypertrophy and retinal vein tortuosity. Of the seven carrier females, five had frequent headaches, four had retinal vessel changes, three had proteinuria with normal renal function, and two had bundle-branch blocks on ECGs. There was no deuteranomalopia in this family, although the inheritance pattern of the Fabry gene is X-linked recessive.     

Spondyloepiphyseal dysplasia tarda in Turner syndrome

A girl with short stature is described in whom chromosomal analysis revealed a 45,X/46,XX mosaicism and in whom radiological investigations disclosed the diagnosis of X-linked spondyloepiphyseal dysplasia tarda. This is the first report of the occurrence of X-linked spondyloepiphyseal dysplasia tarda in a child with Turner syndrome.     

Genetic counselling on brittle grounds: Recurring osteogenesis imperfecta due to parental mosaicism for a dominant mutation

Osteogenesis imperfecta (OI), a dominantly inherited connective tissue disorder, is usually caused by defects in collagen I. There is growing evidence for parental mosaicism that results in affected children born to unaffected parents. This situation poses a difficult task for the geneticist because a mosaic parent may appear clinically healthy while carrying the mutation in a fraction of her or his gonadal cells. To illustrate this problem, we report a Swiss couple whose first child was affected with severe OI. The unexpected recurrence of the disorder in the second child raised the suspicion of a recessive trait or, rather, of parental mosaicism. We identified the responsible collagen mutation in the COL1A2 gene (Gly688Ser in the 2(I)-chain) in both children and demonstrated the father to be a somatic mosaic for this mutation and to have subtle clinical signs such as soft skin and short stature that may be a result of his mosaic state.