P-16

Clinical, biochemical and molecular studies: stepwise to achieve diagnosis of fabry disease

Isaura Ribeiro^I; Sónia Rocha^I; Célia Ferreira^I; Eugénia Pinto^I; Elisabete Silva^I; Fernanda Pinto^I; Helena Ribeiro^I; Domingos Sousa^I; Sara Pacheco^I; Francisco Laranjeira^I; Carla Caseiro^I; Lúcia Lacerda^I

^IUnidade de Bioquímica Genética, Centro de Genética Médica Doutor Jacinto Magalhães, Centro Hospitalar do Porto E.P.E., Porto, Portugal

isaura.ribeiro@chporto.min-saude.pt

Introduction: Fabry  disease (FD, OMIM # 301500), a treatable X-linked storage disorder, is caused by deficient activity of the lysosomal enzyme l1l -galactosidase A (l1l -Gal A). Over 400 pathogenic mutations in GLA gene  have been associated with FD. Enzymatic deficiency leads to lysosomal accumulation of globotriaosylceramide (Gb3) and lyso-Gb3. The first clinical manifestations of FD (pain in the extremities, corneal changes and angiokeratoma) develop in childhood. Progressive renal insufficiency and cardiovascular involvement are the main causes of premature death.

Aims: This work provide evidence for the needful of combining biochemical and molecular tests to diagnose hemizygotes, heterozygotes and symptomatic female carriers of FD.

Methods: FD diagnosis methodologies  underlay  in three approaches:l1l -Gal A activity: measured in capillary Dried Blood Spots (DBS), peripheral blood plasma and total leukocytes, and in cultured skin fibroblasts;GB3: urinary excretion measured in 24 hour urine;Genotype analysis: GLA gene mutations identified by sequencing of exons and exonintron boundaries.

Results: This work report clinical, biochemical and molecular data of 105 patients from 51 unrelated Portuguese families. Partial reduction or absence of l1l -Gal A activity confirmed diagnosis in all male patients. Mutated alleles associated with l1l -Gal A pseudodeficiency may also result in low/reduced l1l -Gal A activity. Wide phenotypic variability in clinical manifestations and biochemical parameters was observed in these cases, which remain to be classified as Fabry patients. In female carriers, l1l -Gal A activity may range from zero to control values, thus, FD diagnosis in females can only be made through molecular genetic tests.

Conclusions: FD diagnosis is not straight forward through l1l -Gal A enzymatic activity, and frequently requires a combination of different technical approaches, even in male patients due to l1l -Gal A pseudodeficiency. X chromosome inactivation can mask obligate carriers, leading to normal l1l -Gal A activity, so molecular analysis is the only effective approach to overcome this obstacle. Identification of a l1l -Gal A mutation associated with a clinically relevant phenotype would be extremely useful for disease progression evaluation, as well as for enzyme replacement therapeutic decisions.