Abetalipoproteinemia typically presents in infancy with failure to thrive, diarrhea, vomiting, and malabsorption of fat. Hematologic manifestations may include acanthocytosis (irregularly spiculated erythrocytes), anemia, reticulocytosis, and hemolysis with resultant hyperbilirubinemia. Malabsorption of fat-soluble vitamins (A, D, E, and K) can result in an increased international normalized ratio (INR). Untreated individuals may develop atypical pigmentation of the retina that may present with progressive loss of night vision and/or color vision in adulthood. Neuromuscular findings in untreated individuals including progressive loss of deep tendon reflexes, vibratory sense, and proprioception; muscle weakness; dysarthria; and ataxia typically manifest in the first or second decades of life.

Congenital defects of bile acid synthesis are autosomal recessive disorders characterized by neonatal onset of progressive liver disease with cholestatic jaundice and malabsorption of lipids and lipid-soluble vitamins from the gastrointestinal tract resulting from a primary failure to synthesize bile acids. Affected infants show failure to thrive and secondary coagulopathy. In most forms of the disorder, there is a favorable response to oral bile acid therapy (summary by Cheng et al., 2003). Genetic Heterogeneity of Congenital Defects in Bile Acid Synthesis There are several disorders that result from defects in bile acid synthesis. See CBAS2 (235555), caused by mutation in the delta(4)-3-oxosteroid 5-beta-reductase gene (AKR1D1; 604741) on chromosome 7q33; CBAS3 (613812), caused by mutation in the 7-alpha hydroxylase gene (CYP7B1; 603711) on chromosome 8q12; CBAS4 (214950), caused by mutation in the AMACR gene (604489) on chromosome 5p13; CBAS5 (616278), caused by mutation in the ABCD3 gene (170995) on chromosome 1p21; and CBAS6 (617308), caused by mutation in the ACOX2 gene (601641) on chromosome 3p14. See also progressive familial intrahepatic cholestasis (PFIC1; 211600), which has a similar phenotype.

Syndrome with characteristics of progressive sensorineural deafness, progressive sensory neuropathy and gastrointestinal abnormalities (progressive loss of gastric motility, small bowel diverticulosis). It has been described in five patients (three sisters in a family and two sisters born to consanguineous parents). This syndrome is transmitted as an autosomal recessive trait.

Congenital bile acid synthesis defect type 4 (BAS defect type 4) is an anomaly of bile acid synthesis (see this term) characterized by mild cholestatic liver disease, fat malabsorption and/or neurological disease.

Congenital pancreatic lipase deficiency is a rare, monoenzymatic form of exocrine pancreatic failure. All reported patients have presented with similar symptoms and clinical findings, including oily/greasy stools from infancy or early childhood and the absence of discernible pancreatic disease. Failure to thrive has not been observed. Analyses of duodenal contents consistently show a marked decrease of pancreatic lipolytic activity (summary by Figarella et al., 1980).

The phenotypic spectrum of ATP8B1 deficiency ranges from severe through moderate to mild. Severe ATP8B1 deficiency is characterized by infantile-onset cholestasis that progresses to cirrhosis, hepatic failure, and early death. Although mild-to-moderate ATP8B1 deficiency initially was thought to involve intermittent symptomatic cholestasis with a lack of hepatic fibrosis, it is now known that hepatic fibrosis may be present early in the disease course. Furthermore, in some persons with ATP8B1 deficiency the clinical findings can span the phenotypic spectrum, shifting over time from the mild end of the spectrum (episodic cholestasis) to the severe end of the spectrum (persistent cholestasis). Sensorineural hearing loss (SNHL) is common across the phenotypic spectrum.

The phenotypic spectrum of ATP8B1 deficiency ranges from severe through moderate to mild. Severe ATP8B1 deficiency is characterized by infantile-onset cholestasis that progresses to cirrhosis, hepatic failure, and early death. Although mild-to-moderate ATP8B1 deficiency initially was thought to involve intermittent symptomatic cholestasis with a lack of hepatic fibrosis, it is now known that hepatic fibrosis may be present early in the disease course. Furthermore, in some persons with ATP8B1 deficiency the clinical findings can span the phenotypic spectrum, shifting over time from the mild end of the spectrum (episodic cholestasis) to the severe end of the spectrum (persistent cholestasis). Sensorineural hearing loss (SNHL) is common across the phenotypic spectrum.

Familial hypercholanemia-1 (FHCA1) is an autosomal recessive disorder characterized by elevated concentrations of bile acids (usually conjugated), itching, and fat malabsorption, leading to poor overall growth and deficiencies of fat-soluble vitamins. Vitamin D deficiency results in rickets, and vitamin K deficiency results in a coagulopathy (Morton et al., 2000; Shneider et al., 1997; summary by Carlton et al., 2003). See also bile acid conjugation defect-1 (BACD1; 619232), which can also show increased bile acid levels, although the bile acids in BACD1 are unconjugated. Genetic Heterogeneity of FHCA See FHCA2 (619256), caused by mutation in the SLC10A1 gene (182396) on chromosome 14q24.

Primary bile acid malabsorption (PBAM) is an intestinal disorder associated with chronic watery diarrhea, excess fecal bile acids, and steatorrhea. Bile acid malabsorption has been classified into 3 main types depending on the etiology. Types 1 and 3 are secondary disorders: type 1 is due to ileal dysfunction resulting from Crohn disease or ileal resection, and type 3 is secondary to other conditions, including cholecystectomy, post-vagotomy, celiac disease, and pancreatic insufficiency. Type 2 bile acid malabsorption is a primary congenital disorder, including the rare type due to mutations in the SLC10A2 gene (review by Pattni and Walters, 2009). Genetic Heterogeneity of Primary Bile Acid Malabsorption Also see PBAM2 (619481), caused by mutation in the SLC51B gene (612085).