Fabry disease (FD) is a rare X-linked lysosomal storage disorder due to mutations in the α-galactosidase A gene (GLA) that result in absent or markedly reduce α-galactosidase A (α-GalA) enzymatic activity. As a result, the major glycosphingolipid substrates, globotriaosylceramide (Gb3) and globotriaosylsphingosine (LysoGb3) accumulate in plasma, urine and tissue lysosomes. In females, the diagnosis can be complicated by the fact that 40-50% of GLA-mutation confirmed heterozygotes have normal or only slightly decreased leukocyte α-GalA activities. Recently, LysoGb3 has been appreciated as a novel FD biomarker, especially for therapeutic monitoring. Among our GLA-mutation proven FD patients, we screened 18 heterozygotes whose leukocyte α-GalA activity was determined at initial diagnosis. For these females, we measured their serum LysoGb3 levels using highly-sensitive electrospray ionization liquid chromatography tandem mass spectrometry. We identified three unrelated females in whom the accumulating LysoGb3 was increased, whereas their leukocyte α-GalA activities were in the normal range. LysoGb3 serves as an useful biomarker to improve the diagnosis of FD heterozygotes and for therapeutic evaluation and monitoring.

Fabry disease is an X-linked lysosomal storage disorder due to α-galactosidase A (α-Gal A) deficiency. Clinical onset of Fabry disease is preceded by significant storage of globotriaosylceramide (Gb3) and related glycosphingolipids, but the extent of the metabolic progression before symptoms is unknown. Using a newly recognized effector and marker of Fabry disease, globotriaosylsphingosine (LysoGb3), we aimed to provide a metabolic picture of classic Fabry disease from the neonatal period to childhood. LysoGb3 was assessed at different times in two brothers with classic Fabry disease (genotype c. 370–2 A > G). The firstborn was diagnosed after clinical onset at 11 years of age, whereas the second-born was diagnosed in the neonatal period. LysoGb3 was measured in dried blood spots by high-sensitive electrospray ionization liquid chromatography tandem mass spectrometry. Blood LysoGb3 concentrations were consistent with patients’ age and clinical picture, with lower levels in the asymptomatic neonate (19.1 ng/ml) and higher levels in the symptomatic child (94.3 ng/ml). In the second-born, LysoGb3 doubled during the first 5 months of life (37.4 ng/ml), reaching ~40% concentration observed in the symptomatic period. The neonatal LysoGb3 concentration in classic Fabry disease exceeded that observed in normal subjects by over 15 times. A substantial increase of LysoGb3 was documented during the first months of life in classic Fabry disease, suggesting an early plateau during the pre-symptomatic period. Such a progressive metabolic trend during the pre-symptomatic period implies the potential definition of a metabolic threshold useful for a preventive therapeutic approach of classic Fabry disease. Additionally, the consistent increase of LysoGb3 in the neonatal period in classic Fabry disease suggests LysoGb3 as a useful marker for improving the specificity of newborn screening for Fabry disease.

Fabry disease (FD) is a rare X-linked lysosomal storage disease caused by mutations in the α-galactosidase A (GLA) gene causing deficiency of α-galactosidase A which results in progressive glycosphingolipid accumulation, especially globotriaosylceramide (Gb3), in body liquids and lysosomes. In a large cohort of FD patients, we aimed to establish genotype/phenotype relations as indicated by serum LysoGb3 (deacylated Gb3). In 69 consecutive adult FD patients (males: n=28 (41%)) with a GLA-mutation confirmed diagnosis, we conducted a multidisciplinary clinical characterization during their routine annual examinations, and measured serum LysoGb3 levels by high-sensitive electrospray ionization liquid chromatography tandem mass spectrometry. Serum levels of LysoGb3 were significantly higher in Classic compared with Later-Onset phenotype and higher in the latter compared with controls, both in males (52 [40-83] vs 9.5 [4.5-20] vs 0.47 [0.41-0.61] ng/ml, P<0.001) and in females (9.9 [7.9-14] vs 4.9 [1.6-4.9] vs 0.41 [0.33-0.48] ng/ml, P<0.001), respectively. Multivariate linear regression analysis showed that LysoGb3 levels were independently associated with, serum creatinine (β=0.09, 95%CI 0.04-0.13, P<0.001) and the presence of cardiomyopathy (β=25, 95%CI 9.8-41, P=0.002). LysoGb3 levels were higher in males with frame-shift and nonsense mutations than in males with missense mutations (84 [72-109] vs 41 [37-52] ng/ml, P=0.002). LysoGb3 relates to disease severity, enzyme replacement response, and to the genotype severity in males. LysoGb3 supports identifying patients at risk who require intensive monitoring and treatment. LysoGb3 appears to be one marker of metabolic phenotyping of FD.

Fabry disease (FD), an X-linked lysosomal storage disorder, results from the deficient activity of α-galactosidase A (α-Gal A) and the accumulation of its substrates, globotriaosylceramide (Gb3) and its deacylated derivative, globotriaosyl-sphingosine (Lyso-Gb3). Here, we compared the levels of Lyso-Gb3 in dried blood spots (DBS) and sera in affected males and heterozygotes with the "Classic" and "Later-Onset" phenotypes. The Lyso-Gb3 concentrations in DBS and sera from 56 FD patients were determined by highly sensitive electrospray ionization liquid chromatography tandem mass spectrometry. The serum Lyso-Gb3 levels in 18 and 5 affected males with the Classic and Later-Onset phenotypes, were 61±38 and 14±12ng/mL, respectively. Lyso-Gb3 levels in 30 females from Classic families and three females from Later-Onset families were 10±5.4 and 2.4±1.0ng/mL, respectively. The linear regression model with serum Lyso-Gb3 as the dependent variable and DBS Lyso-Gb3 an independent variable was described by the function y=-1.83+1.68∗x and showed a high coefficient of determination, R2=0.976. The overall correlation between the Lyso-Gb3 levels in DBS and sera was high (R=0.99; p<0.001). DBS provides a convenient, sensitive, and reproducible source to measure Lyso-Gb3 levels for diagnosis, initial phenotypic assignment, and therapeutic monitoring in patients with Fabry disease.

A fast and reliable method for the determination of hemoglobinopathies and thalassemias by high-resolution accurate mass spectrometry (HRAM/MS) is presented. The established method was verified in a prospective clinical study (HRAM/MS vs. high-pressure liquid chromatography [HPLC]) of 5335 de-identified newborn samples from the Hamburg area. The analytical method is based on a dual strategy using intact protein ratios for thalassemias and tryptic digest fragments for the diagnosis of hemoglobinopathies. Due to the minimal sample preparation and the use of flow injection, the assay can be considered as a high-throughput screening approach for newborn screening programs (2 min/sample). Using a simple dried blood spot (DBS) extraction (tryptic digest buffer), the following results were obtained: (1) a carrier incidence of 1:100 newborns (35 FAS, nine FAC, eight FAD and two FAE), and (2) no homozygous affected patient was detected. Using the HRAM/MS protocol, an unknown Hb mutation was identified and confirmed by genetic testing. In addition to greater specificity toward rare mutations and β-thalassemia, the low price/sample (1–2€) as well as an automated data processing represent the major benefits of the described HRAM/MS method.