Abetalipoproteinemia is a rare autosomal recessive disorder characterized by the inability of the body to absorb lipoproteins from the gastroenterological system due to mutations of proteins responsible for their transport across enterocytes. Diarrhea, failure to thrive, acanthocytosis and central nervous system complications are most important features. The diagnosis requires a thorough diagnostic workup, including laboratory and genetic studies.
The clinical presentation of abetalipoproteinemia (ABL) stems from an insufficient physiological transport of plasma B-containing lipoproteins - chylomicrons, very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL), due to mutations of the microsomal triglyceride transfer protein (MTP), responsible for their transfer through enterocytes [1] [2]. Malabsorption of fat and fat-soluble vitamins, principal pathological events, lead to a very early onset of failure to thrive, reduced growth and severe fatty diarrhea (steatorrhea) [1] [3]. Gradually, diarrhea can subside as patients learn to avoid foods that have shown to induce diarrhea, but the deficiency of fat-soluble vitamins can cause numerous symptoms [1] [3]. Central nervous system damage and visual deficits, due to deficiencies of vitamins E and A, respectively, are most important long-term complications. Reduced deep-tendon reflexes, dysmetria, ataxia, diminished proprioception and vibratory sense, as well as progressive neuropathy, may develop in the first two decades of life [1] [4]. Conversely, pigmentary retinopathy leads to scotomas, loss of color and night vision, and even blindness [1] [4]. Additional complications that have been documented in the literature include coagulopathies (due to vitamin K deficiency), myopathy and demyelination that can cause a spastic gait, while reduced fertility is also reported [1] [2] [4].
Diarrhea and failure to thrive that appears in infancy are strongly suggestive of a malabsorption syndrome. For this reason, a detailed patient history regarding the onset and course of symptoms is detrimental. In addition, a complete physical examination can detect signs of malnourishment, defects in both lower and upper motor neurons, as well as hepatomegaly and visual deficits, strengthening its equally important role in workup [1]. Laboratory studies will reveal minimal or absent low-density lipoprotein (LDL) and triglycerides, whereas increased liver enzymes (alanine and aspartate aminotransferases, or ALT and AST) due to frequent hepatic steatosis are readily observed [2]. A complete blood count (CBC) with a subsequent peripheral blood smear demarcates the presence of acanthocytes, abnormally shaped cells that comprise up to 50% of visible erythrocytes [1] [2], and their presence is considered a cardinal feature of ABL. Moreover, a profoundly reduced erythrocyte sedimentation rate (ESR), anemia and elevated prothrombin time (PT) are other notable findings, suggesting that a full coagulation panel should be included in initial workup [1]. If clinical and laboratory findings provide sufficient evidence to pursue a diagnosis of ABL, genetic testing must be conducted, even without a positive family history, which is common due to the autosomal recessive pattern of inheritance and frequent absence of symptoms in both parents. Detection of mutations in the MTP protein located on chromosome 4q22-24 will confirm the diagnosis [1]. Hepatomegaly may be seen as a result of steatosis of liver. The biopsy of liver in the diseased patients may reveal steatosis along with the raise in the level of serum transaminase.
