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Familial hypobetalipoproteinemia (FHBL) is a disorder that impairs the body's ability to absorb and transport fats, causing low levels of cholesterol in the blood. The severity of the condition varies widely. Mildly affected people may have no signs or symptoms. Many affected people develop an abnormal buildup of fats in the liver (called hepatic steatosis, or fatty liver). In severe cases, this may progress to cirrhosis. Some people also have digestive problems in childhood, resulting in failure to thrive. FHBL is usually caused by mutations in the APOB gene. In a few cases, it may be caused by mutations in other genes, or the cause may be unknown. It is inherited in an autosomal codominant manner; a mutation in one copy of the APOB gene can cause the condition, but changes in both copies of the gene cause more severe symptoms. Management may include reducing fat in the diet and vitamin E supplementation.
Source: GARD Last updated on 05-01-20
The long-term outlook (prognosis) for people with familial hypobetalipoproteinemia (FHBL) can vary considerably. Because it is usually inherited in a codominant manner, a mutation in one copy of the APOB gene can cause the condition, but changes in both copies of the gene can cause more severe symptoms. A person with one mutated copy of the gene is referred to as a heterozygote; a person with 2 mutated copies of the gene is referred to as a homozygote. Furthermore, severity and symptoms in each person can depend on the specific mutation(s) in the gene that each affected person has.
Most people with FHBL are heterozygotes and are generally asymptomatic, but may develop fatty liver. Progression to steatohepatitis (a swollen liver that can cause cirrhosis over time) or the development of other complications is uncommon. To date, only a few case reports linking heterozygotes and severe liver diseases have been published. A few FHBL heterozygotes may have loose stools due to partial fat malabsorption. In some families with a mild (benign) form, longevity has been observed, with many affected people living past the age of 85. Generally, for people with a mild or moderate form of FHBL who do not have destruction of liver cells or fatty liver, the prognosis is very good.
Homozygotes with FHBL are much more rare, and signs and symptoms vary. Some people are asymptomatic or have mild fatty liver disease, while others have severe hepatic steatosis (swelling), intestinal fat malabsorption, failure to thrive, and/or neurological and ocular (eye) dysfunctions. If left untreated, adults can develop retinal degeneration and/or cerebellar dysfunction resulting in ataxia and loss of sensory ability and deep tendon reflexes. Severe vitamin E deficiency is reportedly responsible for the development of neurological symptoms. The development of cirrhosis has been seen in both adulthood and early infancy. Generally, the prognosis is severe when the condition manifests in early childhood.
People with specific questions about how FHBL may affect themselves or family members should speak with a liver specialist or other health care provider.
Last updated on 05-01-20
Familial hypobetalipoproteinemia (FHBL) is estimated to occur in more than 1 in 1000 people in Europe. Some sources report that in the United States, the heterozygous form affects about 1 in 500, while the homozygous form affects about 1 in 1 million. The international frequency is thought to be similar.
Last updated on 05-01-20
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