Fucose supplementation in leukocyte adhesion deficiency type II

Drs Etzioni and Tonetti report on 2 newly discovered leukocyte adhesion deficiency type II (LAD II) patients and their attempts to treat these 2 patients with oral fucose. The treatment did not lead to detectable improvements and did not cause re-expression of the carbohydrate epitope sLex (CD15s). These results need to be compared with our recently published results on the successful treatment of LAD II by oral fucose.1-1 

Taking a closer look at the quantitative details reveals that the fucose doses used in the described therapy were considerably lower than those used in our therapy. Those doses would not have been sufficient to rescue expression of sLex (CD15s) in our patient. Although the presented description of the therapy is very brief, we will try to compare the outcome with our recently published results.

Comparing the fucose doses used by Dr Etzioni with ours clearly shows that they are not sufficient to cause significant expression of the carbohydrate epitope sLex (CD15s). Expression of P-selectin ligands (monitored with P-selectin-IgG) is much earlier observed during fucose therapy and would have been the better epitope to monitor the outcome of the therapy.

The doses reported in the letter are not given as an amount of fucose administered per kilogram of body weight (b.w.) but as a total amount given per day per patient. The body weight of the patient is not reported. Since the starting dose was aimed at 4 daily doses of 200 mg/kg, and a total loading dose of 5 g was given for 1 day, the weight of the baby can be calculated as 6.25 kg. Since we usually give 5 doses per day, this would amount to a single dose of 160 mg/kg in our therapy. This dose was only given for 1 day during therapy of the Arabic patient. We observed significant expression of sLex (15% to 20% of normal expression) only above 5 single daily doses of 250 mg/kg, a dose level that was slowly reached after more than 60 days of treatment during which doses were steadily increased. We continuously increased our doses up to 492 mg/kg, a dose that we reached at day 277 of therapy. We observed the first signs of the expression of P-selectin ligands at a dose above 100 mg/kg.

The starting dose of 5 g/d was given to the Arabic patient only for a single day, followed by 1 week without fucose (according to the graph). The therapy was restarted with half the dose (comparable to single daily doses of 80 mg/kg if 5 doses per day are given, as in our therapy). After 1 month of treatment, the dose was reduced to 1 g/d (32 mg/kg of 5 single doses per day). If we take into account the rapid gain of body weight of a baby over time, these doses per kilogram would in fact be even lower. Clearly, these doses would not have been sufficient to rescue expression of significant amounts of sLex in our patient. No details were reported about the attempted therapy of the second patient (doses, duration of treatment).

In contrast to our paper,1-1 the letter only reports on total peripheral leukocyte counts, not on neutrophil counts. Our patient still has a mild lymphocytosis, leading to mild elevation of total leukocyte counts (12 000 leukocytes/μL). Soon after the onset of therapy, we observed a dramatic reduction of peripheral neutrophil counts.1-1 We agree with Drs Etzioni and Tonetti that treatment of their patient with 2.5 grams fucose per day (corresponding to 5 daily doses of 80 mg/kg) for 1 month might possibly have had a chance to reduce peripheral leukocyte counts in our patient, although treatment with this dose was not long in duration and the dose was at the lower limit. If this were the case, it would argue for a different sensitivity of the LAD II defect to the rescue by externally added fucose. Although unknown, it is still conceivable that the same genes would be mutated in the different patients, since different parts of the molecules could be affected (see below).

The total serum fucose concentrations determined during therapy are surprisingly high, given the low doses of fucose that were administered. Unfortunately, only 2 measurements are documented.

The letter reports that a loading dose of 5 grams of fucose was followed by hypoglycemia. We controlled for this over the whole period of our therapy and never found a sign of hypoglycemia, although for most of our therapy we gave much higher doses of fucose. Considering the biochemical pathways of glucose and fucose and the lack of interaction between them, it is unlikely that application of fucose could cause hypoglycemia.

The letter compares the unpublished therapy data of the 2 new patients with published in vitro data obtained with cells from 1 of the 2 first patients. It is important to keep in mind that these data were obtained with different patients. Determination of reduced GDP-D-mannose-4,6 dehydratase activity in lysates of lymphoblasts were probably obtained with the cells of 1 of the older LAD II patients.1-2 The rescue of α1,6-core fucosylation in fibroblasts and lymphoblastoid cells was also described for cells of 1 of the 2 older patients.1-3 It is unclear whether similar results were obtained for cells of the 2 new patients. It is also unclear from which patient the cells that allowed us to determine that GDP-L-fucose import into Golgi vesicles was defective were isolated (referred to as Tonetti, unpublished results).

We stated in our paper that the psychomotor development of the patient improved during fucose treatment. Indeed, before therapy the patient showed a severe psychomotor retardation, as evidenced by a total score of 28.5 EQ (Griffiths test; 100 EQ is equivalent to the fiftieth percentile).1-4 Reassessment after 3 months of fucose therapy showed a significant increase in psychomotor functioning, with a total score of 45 EQ. But naturally we do not know how the psychomotoric abilities of the patient would have developed in the absence of fucose treatment. Of course, the developmental defects of the patient have not been normalized. We have clearly stated in our paper that “at two years of age the boy is still severely retarded. He does not speak yet, but is able to actively turn around when lying on his back, takes toys that are presented in his hands, and starts to sit briefly without support.”

It is interesting and important that Drs Tonetti and Etzioni have detected a defect in GDP-fucose import into Golgi vesicles of 1 of the 4 Arabic patients (unpublished). Indeed, this would hint at a genetic defect similar to that published in our case.1-5 In agreement with Drs Tonetti and Etzioni, we can well imagine that different mutated alleles of a protein that mediates GDP-fucose import could lead to functional defects of this protein of various severity. Thus, an increase in the cytosolic GDP-fucose level that might be sufficient to overcome a low-efficiency GDP-fucose import in cells that express one mutated allele might not be sufficient to rescue the import in cells expressing another, more severely defective allele. It would be interesting to know whether expression of fucosylated glycoconjugates in cells of the 2 new patients could be rescued by culturing these cells in the presence of externally added fucose and, if so, what fucose concentrations would be necessary. Cloning of the gene(s) coding for a GDP-fucose transporter will allow testing of whether the defect in LAD II is indeed due to mutations in such gene(s). This will also allow researchers to finally determine if and to what extent the molecular defects in different LAD II patients vary.