Report on the International Co-Operative Study of the Effects of L-Selectin Gene Polymorphisms on the Development of Complications in Sickle Cell Disease.
Authors: Okpala Iheanyi , Ugochukwu Cynthia C. , Pantelidis Panagiotis , Inusa Baba , Ibegbulam Obike , Onyekwere Onyinye 
Published: April 2020

Abstract
Our previous study showed that patients with sickle cell disease (SCD) and high steady-state expression of the adhesion molecules L-selectin and αMβ2 integrin on leukocytes developed complications [Blood. 2002;100(suppl):11a. Eur J. Haematol. 2002; 69:135–144]. The aim of this study was to find out if L-selectin protein expression by leukocytes and the development of complications in SCD are affected by previously described single nucleotide polymorphisms within the coding regions of the gene. To detect F206L, T49S and P213S polymorphisms we determined the L-selectin genotype in 142 HbSS patients (64M, 78F, age 2 – 62 yr, mean 27 yr ±12); and 102 racially-matched HbAA controls with similar age and sex distribution. The T49S and P213S amino acid changes in L-selectin are respectively associated with increased risk of vasculopathy and nephropathy; important features of SCD. [Hum Genet. 1996; 97:15–20. Am. J. Hum. Genet.2002; 70: 781–786]. All HbSS patients were evaluated for disease complications. Steady-state expression of L-selectin on neutrophils, lymphocytes and monocytes was measured by flow cytometry in 44 HbSS patients. With respect to F206L polymorphism, 100/142 (70%) patients and 73/102 (72%) controls were FF homozygous, 42 patients and 28 controls were heterozygous FL, and 1 control individual was LL homozygous. There was no significant difference in distribution of the polymorphic variants between patients and controls [Chi-squared (X2) = 0.1, p&gt;0.05]. In codon 213, 48 (33.8%) patients and 42 (41.2%) controls were PP homozygous, 91 patients and 55 controls PS heterozygous, 1 patient and 5 controls SS homozygous [X2 =1.9, p&gt;0.05]. With regard to the T49S polymorphism, 100% of the patients and controls were TT homozygous. At least one complication of SCD was observed in 110 SCD patients; 32 had uncomplicated disease. The most common complications observed were avascular joint necrosis (n=39), sickle nephropathy (n=31), stroke (n=25) and acute chest syndrome (n=20). The observed frequencies of FF genotype in codon 206 among patients with complications (74), and without complication (26) were not significantly different from the expected values [X2 = 2.37, p&gt;0.05]. Similarly, none of the other genotypes (FL, PP, PS) was significantly associated with complications of SCD. Of the 44 patients in who leukocyte L-selectin expression was measured, 31 turned out to be FF homozygous in codon 206, and 13 FL. No significant differences were observed between FF and FL patients in the mean levels of L-selectin expression by neutrophils (FF: 4.00+ 4.56 vs FL: 3.24+ 3.4), monocytes (FF: 4.30+ 5.6 vs FL: 2.56+ 3.39) or lymphocytes (FF: 2.61+ 3.02 vs FL: 2.11+ 2.0); p&gt;0.05. Similarly, the P213S polymorphism had no effect on the level of L-selectin expression. The findings suggest that neither F206L nor P213S L-selectin gene polymorphism predisposes to high leukocyte surface expression of this adhesion molecule, or the development of complications in SCD.