LAD II is an extremely rare immunodeficiency disorder with autosomal recessive inheritance, only a few cases worldwide have been reported. A mutation in the SLC35C1 gene, which encodes for GDP-fucose transporter 1 located in the Golgi apparatus membrane, leads to the absence of fucosylated glycans on the cell surfaces, including CD15 and H blood group substance. While a lack of CD15 on leukocytes prevents adhesion to endothelial cells and transmigration into the tissue, the absence of H substance results in the Bombay blood group phenotype. Clinically patients suffer from recurrent bacterial infections, persistent leukocytosis, developmental delay and an impaired mental capacity.

Here we present a case of a 2-year-old girl with missing expression of CD15 on granulocytes and monocytes in flow cytometry and genetically confirmed LAD II. An immunohematological workup was performed before and after initiation of oral fucose therapy.

The initial serological blood group typing revealed the Bombay phenotype, on molecular level blood group A1O1 was determined. As a sign of missing H substance, serological testing for A1 and H as well as Le(a) and Le(b) on erythrocytes were negative. Indicating the presence of anti-H, the O cell in reverse typing was positive, antibody screening and identification were strongly panreactive and enzyme-resistant (Papain).

About three months after starting fucose therapy, forward typing showed a very weak A antigen after 30 minutes of incubation at room temperature; in reverse typing the reaction with the O cell was significantly weaker. Therefore, the blood type resembled a weak blood group A phenotype. Additionally, the titer of anti-H was clearly weaker compared to the initial testing. To confirm the weak expression of A antigen, after an adsorption with pooled plasma of blood group B with subsequent heat elution, anti-A could be eluted from the patient"s erythrocytes.

In a follow-up sample four months later, the blood group typing showed no visible A antigen, even after 30 minutes of incubation. However, the A antigen was still detectable in adsorption-elution testing.

Oral administration of fucose in a child suffering from LAD II led to a transient and very weak expression of A antigen. Independently of serological results, adsorption-elution studies revealed an A antigen, although it should be noted that this method was not applied to a blood sample before initiation of fucose therapy.

Nothing to disclose.