Congenital disorder of fucosylation type 2c (LADII) presenting with short stature and developmental delay with minimal adhesion defect

Abstract

Leukocyte adhesion deficiency type II is a hereditary disorder of neutrophil migration caused by mutations in the guanosine diphosphate-fucose transporter gene (SLC35C1). In these patients, inability to generate key fucosylated molecules including sialyl Lewis X leads to leukocytosis and recurrent infections, in addition to short stature and developmental delay. We report two brothers with short stature and developmental delay who are compound heterozygotes for novel mutations in SLC35C1 resulting in partial in vivo defects in fucosylation. Specifically, plasma glycoproteins including immunoglobulin G demonstrated marked changes in glycoform distribution. While neutrophil rolling on endothelial selectins was partially impeded, residual adhesion proved sufficient to avoid leukocytosis or recurrent infection. These findings demonstrate a surprising degree of immune redundancy in the face of substantial alterations in adhesion molecule expression, and show that short stature and developmental delay may be the sole presenting signs in this disorder.

Figure 1.

Photos of Proband 1 (left) and 2 (right).

Figure 2.

Characterization of N-glycans from purified IgG heavy chains by normal-phase HPLC. (A) N-Glycans were extracted from purified heavy chains of Probands 1 and 2 (green and red) and from male age matched pediatric controls undergoing evaluation for short stature (black, blue and gray). HPLC tracings normalized to the G1F/G1FB peak reveal that patients 1 and 2 show a striking abundance of afucosylated species (G0, G1, G2), whereas these species represent only a minor fraction of IgG glycans among controls. The letters reflect the specific glycan species shown, including the number of galactoses (G, 0–2), core-fucosylation if present (F) and the presence of a bisecting N-acetylglucosamine if present (B). For example, G1FB defines a monogalactosylated structure with both a core fucose and a bisecting N-acetylglucosamine. (B) HPLC tracings from the same patients and controls following defucosylation, demonstrating normalization of differences; see Figure S1 for before and after tracings from representative patients. (C) Quantitation of non-fucosylated and fucosylated species among agalactosyl (G0 + G0F) IgG heavy chain glycans. *P < 0.05, ***P < 0.001 by Student's t-test. (D) Glycan profiles from patients compared with unaffected family members (mother M, turquoise; father F, purple; sister S, pink). A TSKgel amide-80 column (4.6 mm ID × 15 cm, 3 µm) was used for the separation in (A)–(C), while a TSKgel amide-80 column (4.6 mm ID × 25 cm, 5 µm) was used for separation in (D), accounting for differences in trace profiles.

Figure 3.

Biochemical and functional analysis of granulocytes. (A) Live peripheral blood granulocytes from family members were stained for surface expression of CD15s and PSGL-1. Granulocytes from the probands had profoundly less CD15s expression than the unaffected family members. Conversely, no appreciable difference was observed in expression of PSGL-1 among the family members. (B) Lysates of equivalent granulocyte numbers from all family members were analyzed by western blot, staining for both CD15s and PSGL-1. Granulocytes from the unaffected family members express a 120 kDa CD15s band that corresponds to a 120 kDa PSGL-1 band. Conversely, granulocytes from the affected subjects, while maintaining the PSGL-1 band, are notably lacking CD15s expression. (C) Live peripheral blood granulocytes were perfused over activated HUVEC monolayers under increasing shear stress. Rolling events were totaled over four individual FOV for each shear stress. (D) The velocities of each observed rolling event were also evaluated. At a low shear stress (0.5 dynes/cm²), the total number of rolling granulocytes from the affected individuals were not different from the unaffected family members. However, the rolling velocities of the probands' granulocytes at this shear stress level are significantly faster than the velocities of the unaffected family members.