Table 2. Diagnostic criteria for ABL in Japan.

A.Entry criterion ・Plasma LDL-C level ＜15 mg/dL AND/OR plasma apoB level ＜15 mg/dL. B.Clinical manifestations 1. Gastrointestinal: fat-malabsorption related symptoms (steatorrhea, chronic diarrhea, vomiting, failure to thrive, etc.). 2. Neuromuscular: ataxia, spastic paralysis, hypoesthesia due to peripheral neuropathy, diminution of deep tendon reflexes, etc. 3. Ophthalmological: retinitis pigmentosa, loss of night vision, constriction of visual field, decreased visual acuity, etc. C.Laboratory findings 1. Acanthocytosis D.Differential diagnosis Familial hypobetalipoproteinemia 1 (FHBL1)(OMIM 615558), chylomicron retention disease (Anderson disease) (OMIM 246700), hyperthyroidism. ＊ ABL and homozygous FHBL (Ho-FHBL) can not be distinguished only from the clinical manifestations and laboratory findings of a proband. Family history is helpful. As FHBL1 is an autosomal dominant disorder, obligate heterozygote parents of Ho-FHBL1 patients have ＜50% of normal LDL-C and apoB plasma levels. On the other hand, obligate heterozygote parents of ABL patients have normal plasma lipid levels. Plasma levels of lipids, apoB, and fat-soluble vitamin of other family members may be helpful. E.Genetic test Pathogenic mutations in the MTTP gene <Diagnosis> Definite ABL: Entry criterion (A) is associated with at least one item of B or C AND exclusion of differential diagnosis (D) AND genetic diagnosis (E). Probable ABL: Entry criterion (A) is associated with at least two items of B or C AND exclusion of differential diagnosis (D).