Background. Fabry disease (FD) is an X-linked lysosomal storage and multi-system disorder due to mutations in the a-galactosidase A (a-GalA) gene. We investigated the impact of individual amino acid exchanges in the a-GalA 3D-structure on the clinical phenotype of FD patients. Patients and methods. We enrolled 80 adult FD patients with a-GalA missense mutations and stratified them into three groups based on the amino acid exchange location in the a-GalA 3Dstructure: patients with active site mutations, buried mutations and other mutations. Patient subgroups were deep phenotyped for clinical and laboratory parameters and FD-specific treatment. Results. Patients with active site or buried mutations showed a severe phenotype with multi-organ involvement and early disease manifestation. Patients with other mutations had a milder phenotype with less organ impairment and later disease onset. a-GalA activity was lower in patients with active site or buried mutations than in those with other mutations (P < 0.01 in men; P < 0.05 in women) whilst lyso-Gb3 levels were higher (P < 0.01 in men; <0.05 in women). Conclusions. The type of amino acid exchange location in the a-GalA 3D-structure determines disease severity and temporal course of symptom onset. Patient stratification using this parameter may become a useful tool in the management of FD patients.

Background Although Fabry disease (FD) is an X‐linked lysosomal storage disorder caused by mutations in the α‐galactosidase A gene (GLA), women may develop severe symptoms. We investigated X‐chromosomal inactivation patterns (XCI) as a potential determinant of symptom severity in FD women. Patients and Methods We included 95 women with mutations in GLA (n = 18 with variants of unknown pathogenicity) and 50 related men, and collected mouth epithelial cells, venous blood, and skin fibroblasts for XCI analysis using the methylation status of the androgen receptor gene. The mutated X‐chromosome was identified by comparison of samples from relatives. Patients underwent genotype categorization and deep clinical phenotyping of symptom severity. Results 43/95 (45%) women carried mutations categorized as classic. The XCI pattern was skewed (i.e., ≥75:25% distribution) in 6/87 (7%) mouth epithelial cell samples, 31/88 (35%) blood samples, and 9/27 (33%) skin fibroblast samples. Clinical phenotype, α‐galactosidase A (GAL) activity, and lyso‐Gb3 levels did not show intergroup differences when stratified for X‐chromosomal skewing and activity status of the mutated X‐chromosome. Conclusions X‐inactivation patterns alone do not reliably reflect the clinical phenotype of women with FD when investigated in biomaterial not directly affected by FD. However, while XCI patterns may vary between tissues, blood frequently shows skewing of XCI patterns.