Genetics
Hemoglobin C is produced when a point mutation in the HBB gene causes amino acid substitution of glutamic acid to lysine at the 6th position of the β-globin chain of the hemoglobin. The mutation can be homozygous, occurring on both the chromosomes (alleles), or heterozygous, affecting only one allele. Under heterozygous condition, people are said to have hemoglobin C trait, or as hemoglobin C carriers, and they have one gene for HbC with either one HbA gene or HbS gene. Their red blood cells contain both hemoglobin C and either normal hemoglobin A or hemoglobin S. Hemoglobin C mutation is an autosomal recessive disorder that results from the biparental inheritance of the allele that encodes for hemoglobin C. If both parents are carriers of hemoglobin C, there is a chance of having a child with hemoglobin C disease. Assuming both parents are carriers, there is a 25% chance of having a child with hemoglobin C disease, a 50% chance of having a child who is a carrier of hemoglobin C, and a 25% chance of having a child who is neither a carrier nor affected by hemoglobin C disease.This mutated form reduces the normal plasticity of host erythrocytes causing a hemoglobinopathy. In those who are heterozygous for the mutation, about 28–44% of total hemoglobin (Hb) is HbC, and no anemia develops. In homozygotes, nearly all Hb is in the HbC form, resulting in mild hemolytic anemia, jaundice and enlargement of spleen. Resistance to malaria
Individuals with HbC have reduced risk of P. falciparum malaria infection.
The conus medullaris (Latin for "medullary cone") or conus terminalis is the tapered, lower end of the spinal cord. It occurs near lumbar vertebral levels 1 (L1) and 2 (L2), occasionally lower. The upper end of the conus medullaris is usually not well defined, however, its corresponding spinal cord segments are usually S1-S5. After the spinal cord tapers out, the spinal nerves continue to branch out diagonally, forming the cauda equina.The pia mater that surrounds the spinal cord, however, projects directly downward, forming a slender filament called the filum terminale, which connects the conus medullaris to the back of the coccyx. The filum terminale provides a connection between the conus medullaris and the coccyx which stabilizes the entire spinal cord. Blood supply
The blood supply consists of three spinal arterial vessels—the anterior median longitudinal arterial trunk and the right and left posterior spinal arteries. Other less prominent sources of blood supply include radicular arterial branches from the aorta, lateral sacral arteries, and the fifth lumbar, iliolumbar, and middle sacral arteries. The latter contribute more to the vascular supply of the cauda equina. Pathology
Conus medullaris syndrome is a collection of signs and symptoms associated with injury to the conus medullaris. It typically causes back pain and bowel and bladder dysfunction, spastic or flaccid weakness depending on the level of the lesion, and bilateral sensory loss. Comparatively, cauda equina syndrome may cause radicular pain, bowel/bladder dysfunction, patchy sensory loss or saddle anesthesia and lower extremity weakness at the level of the lumbar and sacral roots.