A Study of Apolipoprotein E (Apo E) Gene Polymorphisms in Chronic Spinal Cord Compression and their Relation with Cervical Spondylotic Myelopathy

Object: Cervical spondylotic myelopathy is a common disease of multifactorial origin
in which neural and vascular processes contribute to the final neurological damage.
Apolipoprotein (Apo) E is a multifunctional protein with central roles in lipid
metabolism and neurobiology. The aim of present study is to determine the possible
relationship of polymorphisms of apolipoprotein E (Apo E) gene with occurrence of
cervical spondylotic myelopathy (CSM) in spinal cord compression patients.
Methods: The present study was carried out on 60 consecutive patients (34 men, 26
women), with spinal cord compression who underwent anterior microsurgical
decompression. The studied subjects were classified into two groups: Group (I): It
included 32 patients with chronic spinal cord compression without cervical
spondylotic myelopathy (18 males and 14 females), Group (II): It included 28
patients with chronic spinal cord compression with cervical spondylotic myelopathy
(16 males and 12 females). Neurological deficits were classified according to the
modified Japanese Orthopedic Association Scale. All studied persons were subjected
to full history taking, general clinical examination, MRI and laboratory investigations
including ApoE genotyping which was carried out by isolation of DNA from venous
blood samples. The APOE genotypes were determined by polymerase chain reaction
followed by restriction enzyme digestion (PCR-RFLP) analysis followed by agarose
gel electrophoresis of digested fragments. Results: The results of the present study
showed a significant increase in group II when compared to group I as regarding the
age (P<0.05), duration of symptoms (P<0.001), number of affected segment
s(P<0.001) and a significant decrease in the diameter of spinal canal (P< 0.001),
whereas no significant difference regarding gender. On comparing the two studied
groups a significant difference was found as regards apolipoprotein E genotype
distribution with increased frequency of the E4 genotype in group II, the E4 allele
was significantly increased in patients with CSM when compared with the other
group without CSM, whereas no significant differences in the distribution of E2 and
E3 alleles. The odds ratio for E4 allele was 3.2 (95% CI: 1.3-9.8). Multiple regression
analysis revealed that duration of symptoms, number of affected segments and
diameter of spinal canal are independent risk factors for CSM. Conclusions: It could
be concluded that E4 polymorphism of the ApoE gene is associated with the
susceptibility to CSM in spinal cord compression and that, longer duration of
symptoms, smaller diameter of spinal canal and more number of affected segments 
are risk factors for such complication. The presence of the ApoE E4 allele is an
independent predictor for presence of CSM. Further studies are needed to evaluate
the type of ApoE polymorphism in patient with improvement or no improvement after
surgery.