<prompt> A 8-yrs-old child has a history since early childhood of malabsorption, ataxia, acanthocytes in the peripheral blood, and very low cholesterol and triglyceride levels. In addition, the patient has been developing progressive, bilateral, concentric contraction of the visual fields and loss of central vision. The underlying pathogenesis of this patients disease isA degenerative disease involving the cerebellumA defect in the synthesis of apolipoprotein BDegeneration of the posterior columns, spinocerebellar tracts, and coicospinal tractsAn absence of high-density lipoproteins  <response>: The patient has abetalipoproteinemia, which is a rare autosomal recessive disease characterized by an absence of apolipoprotein B. Apolipoprotein B is an integral component of chylomicrons, very-low-density lipoproteins VLDL, and low-density lipoproteins LDL. Without the apoprotein, triglyceride and cholesterol cannot be packaged into chylomicrons and VLDL. The disease has its onset in childhood. Malabsorption occurs because dietary fat cannot be packaged into chylomicrons, and intestinal cells fill with lipid. This blocks the reabsorption of fat and other nutrients. Loss of essential fatty acids results in membrane abnormalities in red blood cells with production of acanthocytes thorny-appearing cells. Neurologic findings, including ataxia, nystagmus, and sensory abnormalities, also occur.. 