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.

We describe two female monozygotic (MZ) twins heterozygous for Fabry disease, an X linked disorder resulting from the deficient activity of alpha-galactosidase A. While one of the twins was clinically affected, the other was asymptomatic. Enzymatic assay of alpha-galactosidase in blood leucocytes, skin fibroblasts, Epstein-Barr virus transformed lymphoid cell lines, and hair follicles of the twins and their parents confirmed the heterozygous status of the twins and indicated that Fabry disease had occurred as a result of a de novo mutation. The son of the unaffected twin sister was shown to be hemizygous. Molecular analysis of the alpha-galactosidase A gene permitted the identification of an as yet undescribed point mutation at position 10182 of exon 5 which causes an Asp to Asn substitution at codon 231. Single strand conformation polymorphism (SSCP) analysis again showed the heterozygous status of the twins and a normal pattern in their parents. The basis for the discordant expression of this d novo mutation in the twins was investigated by studying their X inactivation status. Analysis of the inactive X specific methylation at the androgen receptor gene showed unbalanced inactivation in the twins' fibroblasts and in opposite directions. While the maternally derived X chromosome was preferentially active in the asymptomatic twin, the paternal X chromosome was active in the other, affected twin and was found in her hemizygotic nephew. These data suggest that the paternal X chromosome carries the de novo alpha-galactosidase A mutation and that uneven X inactivation is the underlying mechanism for disease expression in this novel female MZ twin pair. This is the first documented case of female twins discordant for Fabry disease

Isolated and contiguous glycerol kinase gene disorders: a review

Glycerol kinase deficiency (GKD) is an X-linked recessive disorder. There are two types. an isolated form and a complex form. We review the clinical, biochemical and molecular genetic features of GKD. The clinical and biochemical phenotype of isolated GKD may vary from a life-threatening childhood metabolic crisis to asymptomatic adult 'pseudohypertriglyceridaemia', resulting from hyperglycerolaemia. To date 38 patients from 24 families with isolated GKD have been reported. At least 7 of these patients had a metabolic crisis during a catabolic condition. The complex GKD is an Xp21 contiguous gene syndrome involving the glycerol kinase locus together with the adrenal hypoplasia congenita (AHC) or Duchenne muscular dystrophy (DMD) loci or both. Clinical features of a patient with complex GKD depend on the loci that are involved. Approximately 100 patients from 78 families with a complex GKD have been reported. Seventeen patients with complex GKD (AHC-GKD-DMD or AHC-GKD) died in the neonatal period or early childhood because of unrecognized or inappropriate management of adrenal dysfunction. Since the outcome of the crisis in GKD is highly dependent on the physicians' knowledge of the disease, we devised an algorithmic approach to the diagnosis. From molecular genetic investigations of isolated GKD, 7 missense mutations, 2 splice site mutations, I nonsense mutation, 1 Alu Sx insertion and 2 small deletions were reported for isolated GKD in 13 unrelated families. In 4 families consisting of more than one patient with the same biochemical and genetic defect, the phenotypic variability of the isolated GKD was remarkable. The clinical variability in isolated GKD cannot be explained by biochemical or by molecular heterogeneity. Isolated GKD patients showed a tendency towards hypoglycaemia with hyperketonaemia; whether the clinical symptoms of GKD are caused by dysfunction of gluconeogenesis and/or ketolysis needs to be investigated furthe

Spectrum of mutations in the fumarylacetoacetate hydrolase gene of tyrosinemia type 1 patients in northwestern Europe and Mediterranean countries

Hereditary tyrosinemia type 1 (HT1) is a rare metabolic disease caused by a deficient activity of the enzyme fumarylacetoacetase (FAH). To investigate the molecular heterogeneity of tyrosinemia, the geographic distribution and the genotype-phenotype relationship, we have analyzed the FAH genotype of 25 HT1 patients. Mutation screening was performed by PCR amplification of exons 1-14 of the FAH gene, followed by SSCP analysis and direct sequencing of the amplified exons. Fourteen different mutations were found, of which seven were novel, viz. three missense mutations (G158D, P261L, F405H), a deletion of three nucleotides causing a deletion of serine (DEL366S) and three splice site mutations: IVS2+1(g-t), IVS6-1(g-c), IVS8-1(g-c). The splice site mutations IVS6-1(g-t) and IVS12+5(g-a) were frequently found in countries around the Mediterranean and northwestern Europe, respectively. No clear correlation between the genotype and the three major HT1 subtypes could be establishe

Influence of the type of F8 gene mutation on inhibitor development in a single centre cohort of severe haemophilia A patients

The development of neutralizing antibodies against factor VIII (FVIII) is a major complication of treatment with FVIII in patients with severe haemophilia A. This study was designed to describe the relationship between the type and location of the factor 8 (F8) gene mutation and the development of clinically relevant inhibitors in patients with severe haemophilia A. We conducted a single centre cohort study among 318 consecutive patients (baseline FVIII activity level <0.01 IU mL(-1)) born between 1934 and 2007 who were treated with FVIII on at least 50 exposure days. The primary outcome was clinically relevant inhibitor development, defined as the occurrence of at least two positive inhibitor titres and a decreased recovery. Clinically relevant inhibitors were diagnosed in 14% (43) of patients (30 high-titre). The cumulative incidence of inhibitor development was 18% (35 of 200) in high-risk gene defects (67% in patients with large deletions, 30% in patients with nonsense mutations, 15% in patients with intron 1 or 22 inversions) and 7% (8 of 118) in low-risk gene defects (7% in patients with small deletions and insertions, 6% in patients with missense mutations, 8% in patients with splice site mutations). In patients with point mutations, the cumulative risk of developing inhibitors was highest in patients with mutations in the A3 and C2 domains (13% and 17% respectively). In conclusion, in agreement with earlier observations, the type and location of the F8 gene mutation were important determinants of inhibitor development in patients with severe haemophilia

Clinical heterogeneity and novel mutations in the glycerol kinase gene in three families with isolated glycerol kinase deficiency.

Isolated glycerol kinase deficiency (GKD) is an X linked recessive disorder. The clinical and biochemical picture may vary from a childhood metabolic crisis to asymptomatic adult "pseudohypertriglyceridaemia", the result of hyperglycerolaemia. We performed glycerol kinase (GK) gene analysis to study the molecular heterogeneity and genotype-phenotype correlation in eight males from three families with isolated GKD. All patients had hyperglycerolaemia and glyceroluria. Four patients from two families were essentially free of symptoms. Three patients had gastrointestinal symptoms with ketoacidosis or hypoglycaemia or both. One patient had recurrent convulsions as the only acute sign, without evidence that it was correlated with a catabolic state. Fasting tests in two symptomatic patients of family 1 showed hyperketotic states, together with a tendency to hypoglycaemia. The diagnosis was confirmed by a defective 14C-glycerol incorporation into trichloroacetic acid precipitable macromolecules in intact skin fibroblasts. Mutation screening of the GK gene was performed by amplification and direct sequencing of exons using PCR. Three novel mutations were identified: (1) a deletion starting downstream of exon 9, extending to the 3' end of the gene; (2) a nonsense mutation R413X caused by a C1351T transition; and (3) a missense mutation W503R caused by a T1651C transition. In addition, we found differences from the reported sequence: (1) exon 9 actually consists of two exons, which consequently will change the number of GK gene exons from 19 to 20 exons, and (2) nucleotide differences in exon 19. So far, no genotype-phenotype correlation can be established in these GKD families

Genotype‐phenotype relationship in hereditary haemorrhagic telangiectasia

Hereditary haemorrhagic telangiectasia (HHT) is an autosomal dominant disorder characterised by vascular malformations in multiple organ systems, resulting in mucocutaneous telangiectases and arteriovenous malformations predominantly in the lungs (pulmonary arteriovenous malformation; PAVM), brain (cerebral arteriovenous malformation; CAVM), and liver (hepatic arteriovenous malformation; HAVM). Mutations in the ENG and ALK‐1 genes lead to HHT1 and HHT2 respectively. In this study, a genotype‐phenotype analysis was performed. A uniform and well classified large group of HHT patients and their family members were screened for HHT manifestations. Groups of patients with a clinically confirmed diagnosis and/or genetically established diagnosis (HHT1 or HHT2) were compared. The frequency of PAVM, CAVM, HAVM, and gastrointestinal telangiectases were determined to establish the genotype‐phenotype relationship. The analysis revealed differences between HHT1 and HHT2 and within HHT1 and HHT2 between men and women. PAVMs and CAVMs occur more often in HHT1, whereas HAVMs are more frequent in HHT2. Furthermore, there is a higher prevalence of PAVM in women compared with men in HHT1. In HHT1 and HHT2, there is a higher frequency of HAVM in women. HHT1 has a distinct, more severe phenotype than HHT2. There is a difference in the presence of symptoms between men and women. With these data, genetic counselling can be given more accurately when the family mutation is known