Systematic cascade screening in the Danish Fabry Disease Centre: 20 years of a national single-centre experience

Abstract

The lysosomal storage disorder Fabry disease is caused by deficient or absent activity of the GLA gene enzyme α-galactosidase A. In the present study we present the molecular and biochemical data of the Danish Fabry cohort and report 20 years' (2001-2020) experience in cascade genetic screening at the Danish National Fabry Disease Center. The Danish Fabry cohort consisted of 26 families, 18 index patients (9 males and 9 females, no available data for 8 index-patients) and 97 family members with a pathogenic GLA variant identified by cascade genetic testing (30 males and 67 females). Fourteen patients (5 males and 9 females; mean age of death 47.0 and 64.8 years respectively) died during follow-up. The completeness of the Fabry patient identification in the country has resulted in a cohort of balanced genotypes according to gender (twice number of females compared to males), indicating that the cohort was not biased by referral, and further resulted in earlier diagnosis of the disease by a lower age at diagnosis in family members compared to index-patients (mean age at diagnosis: index-patients 42.2 vs. family members 26.0 years). Six previously unreported disease-causing variants in the GLA gene were discovered. The nationwide screening and registration of Fabry disease families provide a unique possibility to establish a complete cohort of Fabry patients and to advance current knowledge of this inherited rare lysosomal storage disorder.

Fig 1. Flow chart of the principle of the procedure of the cascade screening.

Cascade screening begins once an index-case has been identified. Three generations surrounding the index-case are genetically screened. Each time a family member with a pathogenic GLA variant is identified, the procedure is repeated. When the index-case/family member with a pathogenic GLA variant was male, his mother, his daughter and all his siblings were offered testing. When the index-case/family member with a pathogenic GLA variant was female, both her parents, and all her children were offered testing and depending on the parents’ result, either only her female siblings in case of a father with pathogenic GLA variant or all her siblings in case of a mother with pathogenic GLA variant were tested (♂ = male, ♀ = female).

Fig 2. Structure of human GLA and positions of the amino acid substitutions resulting from the missense pathogenic variants identified in the Danish Fabry patients.

The backbone is displayed as a ribbon model, and the ligand and sugars as a stick model. The amino acids involved in the substitutions and the catalytic residues (D170 and D231) are indicated as a space-filling calotte (Corey-Pauling-Koltun CPK) model. Front view (top) and back view (bottom).

Fig 3. Residual α-galactosidase A activity in Fabry males and females.

Activity is expressed, as nmol/h/mg protein. Grey area represents the normal α-galactosidase A activity range (20–65 nmol/h/mg protein). Available measurements in n = 35/39 males and females n = 61/76 females. ****: p-value <0.001.