eMedicine Specialties > Endocrinology > Metabolic Disorders

Low LDL Cholesterol (Hypobetalipoproteinemia)

Vibhuti N Singh, MD, MPH, FACC, FSCAI, Director, Suncoast Cardiovascular Center; Chair, Cardiology Division and Cath Labs, Department of Medicine, Bayfront Medical Center; Clinical Assistant Professor, Division of Cardiology, University of South Florida College of Medicine
Elena Citkowitz, MD, PhD, FACP, Clinical Professor of Medicine, Yale University School of Medicine; Director, Cholesterol Management Center, Director, Cardiac Rehabilitation, Department of Medicine, Hospital of St Raphael

Updated: Aug 4, 2009

Introduction

Background

Abetalipoproteinemia (ABL) and familial hypobetalipoproteinemia (FHBL) are relatively uncommon inherited disorders of lipoprotein metabolism that cause low cholesterol levels. Although persons whose low-density lipoprotein (LDL) cholesterol levels are moderately low (ie, individuals with FHBL) exhibit an enhanced tendency to develop fatty liver disease (FLD),^{[1 ]}persons with a profound reduction of LDL cholesterol may have a decreased risk for heart disease.

ABL is a rare disease associated with a unique plasma lipoprotein profile in which LDL and very low-density lipoprotein (VLDL) are essentially absent. The disorder is characterized by fat malabsorption, spinocerebellar degeneration, acanthocytic red blood cells, and pigmented retinopathy. It is caused by a homozygous autosomal recessive mutation in the gene for microsomal triglyceride transfer protein (MTP). MTP mediates intracellular lipid transport in the intestine and liver and thus ensures the normal function of chylomicrons (CMs) in enterocytes and of VLDL in hepatocytes.^{[2 ]}

Affected infants may appear normal at birth, but by the first month of life, they develop steatorrhea, abdominal distention, and growth failure. Children develop retinitis pigmentosa and progressive ataxia, with death usually occurring by the third decade. Early diagnosis, high-dose vitamin E (tocopherol) therapy, and medium-chain fatty acid dietary supplementation may slow the progression of the neurologic abnormalities. Obligate heterozygotes (ie, parents of patients with ABL) have no symptoms and no evidence of reduced plasma lipid levels.

FHBL is also a rare disorder of apolipoprotein B (apoB) metabolism characterized by levels of plasma cholesterol and LDL cholesterol that are less than one-half normal in heterozygotes and are very low (<50 mg/dL) in homozygotes. FHBL is caused by an autosomal, codominant mutation in the gene for apoB (APOB), which is carried on chromosome 2. This mutation results in a truncated form of apoB.^{[3,4 ]}Homozygotes present with fat malabsorption and low plasma cholesterol levels at a young age. They develop progressive neurologic degenerative disease, retinitis pigmentosa, and acanthocytosis, similar to patients with ABL. Although heterozygotes are usually asymptomatic, they exhibit decreased LDL cholesterol and apoB levels and possibly have a decreased risk of atherosclerosis.^{[5 ]}

The nonfamilial forms of hypobetalipoproteinemia are secondary to a number of clinical states, such as occult malignancy, malnutrition, and chronic liver disease.

Pathophysiology

Cholesterol and triglycerides are transported from sites of synthesis to sites of utilization in the form of lipoproteins. These particles consist of a core of cholesterol esters and triglycerides surrounded by a monolayer of free cholesterol, phospholipids, and proteins (apolipoproteins). The 4 major lipoproteins are very low-density lipoprotein (VLDL), low-density lipoprotein (LDL), high-density lipoprotein (HDL), and chylomicrons (CMs). VLDL and CMs are assembled within the lumen of the endoplasmic reticulum of hepatocytes and enterocytes, respectively, transported to the Golgi complex, and then secreted into the circulation.

Each lipoprotein is characterized by its lipid composition and by the type and number of apolipoproteins it possesses. CMs, VLDL, and LDL carry apolipoproteins on their surface; these apolipoproteins have lipid-soluble segments, the beta apolipoproteins, which remain part of the lipoprotein throughout its metabolism. Other apolipoproteins (A, C, D, E, and their subtypes) are soluble and are exchanged between lipoproteins during metabolism.

Beta apolipoproteins

Beta apolipoproteins are the largest of the apolipoproteins. They are critically important for the formation and secretion of CMs and VLDL; abnormalities that impede this process result in abetalipoproteinemia (ABL) and hypobetalipoproteinemia.

The 2 beta apolipoproteins are B-100 and B-48. ApoB-100 is carried on VLDL and the lipoproteins derived from its metabolism, including VLDL remnants or intermediate-density lipoprotein and LDL. ApoB-100, which is synthesized by the liver, is larger than apoB-48, being made up of 4536 amino acids. Unlike apoB-48, apoB-100 contains the binding site essential for LDL uptake by hepatocyte LDL receptors.^{[6 ]}ApoB-48 is carried on CMs, is derived from the same gene as apoB-100, and is approximately half its size, consisting of 2152 amino acids.

Abetalipoproteinemia

MTP gene mutation

Formation and exocytosis of CMs at the basolateral membrane of intestinal epithelial cells is necessary for the delivery of lipids to the systemic circulation. One of the proteins required for the assembly and secretion of CMs is MTP. The gene for this protein (MTP) is mutated in patients with ABL.^{[7,8 ]}

Several mutations in the MTP gene have been described. In most patients with ABL, the mutation involves a gene encoding the 97-kd subunit of MTP. Consequently, children with ABL develop fat malabsorption and, in particular, suffer the results of vitamin E deficiency (ie, retinopathy, spinocerebellar degeneration).^{[9 ]}Biochemical test results show low plasma levels of apoB, triglycerides, and cholesterol. Membrane lipid abnormalities also affect the erythrocytes, causing acanthocytosis (burr cells). Long-chain fatty acids are very poorly absorbed, and the intestinal epithelial cells become engorged with lipid droplets. Such children respond to a low-fat diet rich in medium-chain fatty acids, as well as to supplementation with high-dose, fat-soluble vitamins, especially vitamin E.^{[10 ]}

Role of vitamin E

Most of the clinical symptoms of ABL are the result of defects in the absorption and transport of vitamin E. Normally, vitamin E is transported from the intestine to the liver, where it is repackaged and incorporated into the assembling VLDL particle by the tocopherol-binding protein. In the circulation, VLDL is converted to LDL, and vitamin E is transported by LDL to peripheral tissues and delivered to cells via the LDL receptor. Patients with ABL are markedly deficient in vitamin E because of the deficient plasma transport of vitamin E, which requires hepatic secretion of apoB-containing lipoproteins. Most of the major clinical symptoms, especially those of the nervous system and retina, are primarily due to vitamin E deficiency. This hypothesis is supported by the fact that other disorders involving vitamin E deficiency are characterized by similar symptoms and pathologic changes.^{[8 ]}

Familial hypobetalipoproteinemia

APOB gene mutation

FHBL is a rare autosomal dominant disorder of apoB metabolism. Most cases of known origin result from mutations in the APOB gene, involving 1 or both alleles. More than 30 mutations have been described. Most often, a mutation involving a 4–base–pair deletion in the APOB gene prevents translation of a full-length apoB-100 molecule, leading to the formation of truncated apoB molecules (apoB-37, with 1728 amino acids; apoB-46, with 2057 amino acids; or apoB-31, with 1425 amino acids).^{[3,4,11,12 ]}

Metabolic turnover studies indicate that in some persons, these APOB gene mutations result in impaired synthesis of apoB-containing lipoproteins, and that in other patients, they cause increased catabolism of these proteins. Overall, beta-lipoprotein levels remain low.

Heterozygotes may have LDL cholesterol levels less than or equal to 50 mg/dL, but they often remain asymptomatic and have normal life spans. In the homozygous state, the absence of apoB leads to significant impairment of intestinal CM formation, which in turn leads to impaired absorption of fats and fat-soluble vitamins. Cholesterol absorption may also be impaired. Subsequent vitamin E malabsorption results in low tissue stores of vitamin E and leads to the development of degenerative neurologic disease.^{[4 ]}

Secondary causes

The secondary causes of hypobetalipoproteinemia include occult malignancy, as well as conditions such as malnutrition, liver disease, and chronic alcoholism. These conditions must be excluded before the diagnosis of FHBL can be made.

Frequency

United States

Abetalipoproteinemia (ABL) and familial hypobetalipoproteinemia (FHBL) are rare inborn errors of lipoprotein metabolism. ABL occurs in less than 1 in 1 million persons. FHBL occurs in approximately 1 in 500 heterozygotes and in about 1 in 1 million homozygotes. Approximately one third of ABL and FHBL cases result from consanguineous marriages.

International

Frequency is similar to that reported in the United States.

Mortality/Morbidity

• Abetalipoproteinemia (ABL) - Infants exhibit failure to thrive, with fat malabsorption and abdominal distention occurring during the first month of life. Spinocerebellar degeneration and pigmented retinopathy develop during childhood. Death usually occurs by the third decade. Obligate heterozygotes are asymptomatic and have normal plasma lipid levels; their risk of developing cardiovascular disease is probably lower than average.
  
  The most prominent and debilitating clinical manifestations of ABL in adults are neurologic in nature and usually manifest for the first time in the second decade of life. Severe ataxia and spasticity develop by the third or fourth decade. Progressive central nervous system involvement is the eventual cause of death in most patients and often occurs by the fifth decade. Moreover, ophthalmic symptoms begin with decreased night and color vision, with progression to virtual blindness by the fourth decade.
• Familial hypobetalipoproteinemia (FHBL) - Homozygotes are identified at a young age because of fat malabsorption and through the detection of decreased plasma cholesterol levels. A deficiency of fat-soluble vitamins may lead to retinitis pigmentosa, acanthocytosis (or burr cells due to altered red blood cell membrane lipids), and progressive, degenerative neurologic disease. Heterozygotes are asymptomatic and are often diagnosed when routine lipid screening discloses abnormally low plasma cholesterol levels. Fat malabsorption is rarely noted. Neurologic examination may reveal diminished or absent deep tendon reflexes and, less frequently, deficits in proprioception and ataxia. The syndrome is associated with normal longevity. Compound heterozygotes (ie, patients with mutations of the APOB gene at 2 different sites) have a clinical presentation similar to that of homozygotes.

Race

No race predilection for abetalipoproteinemia or familial hypobetalipoproteinemia has been described. Cases have been reported from every continent.

Sex

No sex predilection for abetalipoproteinemia or familial hypobetalipoproteinemia has been noted. Both disorders are caused by a mutation on an autosomal chromosome.

Age

The homozygous disorders are identified during infancy or childhood.

• Persons with homozygous abetalipoproteinemia (ABL) are detected in the first decade of life. Heterozygotes are asymptomatic throughout life.
• Familial hypobetalipoproteinemia heterozygotes are carriers of the recessive gene that leads to ABL and are asymptomatic. Heterozygotes are usually identified in adulthood after routine blood work, lipid screening, or a workup for gastrointestinal (GI) or neurologic disorders.

Clinical

History

The phenotypic expression of homozygous abetalipoproteinemia (ABL) is essentially the same as that for homozygous familial hypobetalipoproteinemia (FHBL). Chylomicrons (CMs), very low-density lipoprotein (VLDL), and low-density lipoprotein (LDL) are essentially absent. Severe fat malabsorption and all of the sequelae of that condition are present during infancy and beyond. ABL, if left untreated, can result in early mortality.

A study by Sankatsing and colleagues of patients with FHBL evaluated (a) the arterial wall stiffness and carotid intima-media thickness (IMT), measured by B-mode ultrasonography, as noninvasive, surrogate markers for cardiovascular disease (CVD), and (b) the presence and severity of hepatic steatosis, as assessed by abdominal ultrasonography.^{[13 ]}The hepatic transaminase levels were found to be only modestly elevated, although the prevalence (54% vs 29%; P = 0.01) and severity of steatosis were significantly higher in individuals with FHBL than they were in controls. Furthermore, despite similar IMT measurements, arterial stiffness was significantly lower in patients with FHBL (P = 0.04) than it was in controls, suggesting cardiovascular protection.

Heterozygotes with the mutation that leads to either ABL or FHBL are generally asymptomatic. However, because FHBL is a codominant condition (unlike ABL, which is a recessive disorder), carriers have half the normal levels of beta lipoproteins. Cholesterol levels range from 40-180 mg/dL. Some carriers may present with signs and symptoms of neurologic involvement.

• Failure to thrive in infancy
  • Homozygous ABL and homozygous FHBL are associated with severe fat malabsorption from birth.
  • Children fail to thrive during first year of life.
• Gastroenterologic symptoms
  • Steatorrhea and diarrhea are present.
  • Stools are pale, malodorous, and bulky.
  • The abdomen may be distended.
  • In patients older than 10 years, intestinal symptoms tend to be less severe, probably due, in part, to the learned avoidance of high fat intake.
• Neurologic symptoms
  • Intellectual development tends to be slow.
  • Deep tendon reflexes are absent.
  • Patients develop peripheral neuropathy.
  • Loss of position and vibration sense occurs.
  • Intention tremors develop.
• Ophthalmologic symptoms
  • Retinitis pigmentosa occurs in adolescents.
  • Symptoms begin with decreased night and color vision.
  • Daytime visual acuity gradually deteriorates.
  • Virtual blindness occurs by the fourth decade of life.

Physical

The physical examination usually reveals fat malabsorption stigmata, spinocerebellar tract involvement, and ocular involvement. Some of the signs encountered due to fat malabsorption may include the following:

• Gastroenterologic - Patients may have abdominal distension.
• Neurologic
  • The first sign of disease is usually the loss of deep tendon reflexes.
  • Next, distal lower extremity vibratory and proprioceptive senses decrease.
  • Cerebellar signs, such as dysmetria, ataxia, and spastic gait, then ensue.
  • Finally, patients develop extensor plantar responses.
• Ophthalmologic
  • Patients develop angioid streaks and retinal degeneration (or retinitis pigmentosa).^{[14 ]}
  • Ophthalmoplegia is also reported.
• Hepatic - Patients may have an enlarged, fatty liver with signs of chronic liver disease (eg, cirrhosis).

Causes

Abetalipoproteinemia (ABL) and familial hypobetalipoproteinemia (FHBL) are caused by genetic defects that encode for MTP or apoB molecules, respectively.

• ABL is caused by mutations in the MTP gene.
• FHBL is caused by a mutation in the APOB gene.
• Secondary hypobetalipoproteinemia may be associated with cancers, liver disease, severe malnutrition, and other wasting disorders.

Differential Diagnoses

Other Problems to Be Considered

Anderson disease (CM retention disease)^{[15 ]}
Disorders of fat malabsorption
Ataxia
Spinocerebellar disorders
Retinal degeneration
Secondary cancers
Friedreich disease
Hereditary sensorimotor neuropathies
Combined neuropathy and ataxia
Familial vitamin E deficiency
Chronic cholestatic liver disease
Machado-Joseph disease

Workup

Laboratory Studies

• Routine complete blood cell count with differential, including platelet count - Some patients present with thrombocytopenia. In the absence of another obvious explanation, a low platelet count may be considered secondary to vitamin cofactor malabsorption, and one must consider the possibility of abetalipoproteinemia (ABL) and familial hypobetalipoproteinemia (FHBL).
• Blood smear to assess erythrocyte morphology - Acanthocytosis (burr cells) may be evident in patients with FHBL, but even when the erythrocytes appear normal, an exceptionally low sedimentation rate can be demonstrated. Patients with ABL uniformly demonstrate acanthocytosis. From 40-80% of erythrocytes are acanthocytic. Mild to moderate anemia with mild to moderate reticulocytosis may also be present.
• Basic chemistry (metabolic) panel - This test is used to exclude multisystem illness or evidence of malnutrition from another cause.
• Liver function tests, including transaminases - Hepatic transaminases have been reported to be elevated in patients with ABL and FHBL. The mechanism for this finding is unclear.^{[16 ]}
• Stool studies - Search the stool for ova, parasites, and white blood cells in order to exclude other common causes of fat malabsorption.
• Fasting lipid profile - A fasting lipid profile should be obtained from patients and their first-degree relatives, in the latter case to assist in distinguishing between ABL and homozygous FHBL. The parents of a patient with ABL have normal cholesterol levels, while the parents of a patient with homozygous FHBL have lower-than-average cholesterol levels.
  • Heterozygous FHBL - Patients with heterozygous FHBL may have total cholesterol levels that are below the fifth percentile (and may be less than 100 mg/dL). Plasma low-density lipoprotein (LDL) cholesterol levels are also reduced by one half or more. High-density lipoprotein (HDL) cholesterol levels are normal or slightly increased. Plasma triglyceride levels are reduced in some kindreds.
  • Homozygous FHBL - Patients with homozygous FHBL show extremely low plasma cholesterol and triglyceride levels.
  • ABL - Characteristically, extremely low levels of plasma cholesterol (<50 mg/dL) and triglycerides are detected in infants and young children. Patients who are obligate heterozygotes have normal cholesterol levels.
• ABL or homozygous FHBL diagnosis - This depends on finding acanthocytes in the peripheral blood and extremely low plasma levels of cholesterol (<50 mg/dL). Chylomicrons (CMs) and very low-density lipoprotein (VLDL) are not detectable, and LDL is virtually absent.

Imaging Studies

• Hepatic scan or ultrasonography to assess changes of fatty liver - Patients with liver enlargement, splenomegaly, or elevated levels of transaminases may need hepatic imaging studies to ascertain anatomy and function.
• Magnetic resonance imaging (MRI) of the spinocerebellar region - This may become necessary in patients presenting with ataxic gait or vision loss.
• Eye and retinal examination and imaging - An ophthalmic examination and retinal imaging may be needed in patients with visual disturbance and retinal degeneration.

Other Tests

• The molecular diagnosis of familial hypobetalipoproteinemia can be performed only in specialized laboratories; it is accomplished through the examination of the plasma apoB, using gel electrophoresis or deoxyribonucleic acid (DNA) analysis to identify specific mutations.
• The demonstration of the molecular defect in persons with abetalipoproteinemia requires a specialized laboratory for the detection of low or absent MTP in intestinal biopsy specimens or DNA analysis to identify specific mutations.

Procedures

• Intestinal biopsy may be needed, along with electron microscopy.
  • The endoscopic appearance of the mucosa of the small intestine may be whitish, although this characteristic is usually limited to the villi.
  • The diagnosis is confirmed by the typical hematologic finding of acanthocytosis and the appearance of the small-bowel biopsy specimen, in which the tip enterocytes are filled with lipid droplets. The villi are normal but are lined with fat-containing enterocytes (engorged with triglycerides) that constitute the lipid droplets.
  • In specialized cases, light and transmission electron microscopy may show fat-loaded enterocytes (from marked triglyceride accumulation).
• Liver biopsy is rarely needed but may become necessary to assess for fatty liver, chronic liver disease, or cirrhosis and to rule out other causes of hepatomegaly, fatty liver, and transaminase elevation.

Histologic Findings

Intestinal biopsy reveals the gross appearance of white mucosa, usually limited to the villi. Histologically, the villi are normal but are lined with fat-containing enterocytes (engorged with triglycerides). In specialized cases, light and transmission electron microscopy may show fat-loaded enterocytes.

Treatment

Medical Care

Abetalipoproteinemia (ABL) and familial hypobetalipoproteinemia (FHBL) are rare genetic disorders. Infants and children who present with homozygous FHBL or ABL require early treatment with very high doses of vitamin E. Management in adults includes treatment of the complications of the disorders.

To prevent the neurologic manifestations that occasionally occur with FHBL, heterozygous patients receive modest supplementation with vitamin E.

• Dietary manipulation^{[4 ]}
  • Severe restriction of long-chain fatty acids to 15 g per day is recommended to improve the complications of fat malabsorption.
  • In infants with failure to thrive, brief supplementation with medium-chain triglycerides may be necessary, but the amount must be closely monitored to avoid liver toxicity.
• Vitamin supplementation^{[4 ]}
  • Very large doses of oral vitamin E (100-300 mg/kg/d) are used to raise the tissue vitamin E concentration and to prevent neurologic complications in homozygotes.
  • Heterozygotes with FHBL should receive modest doses of vitamin E to prevent the development of neurologic complications.
  • Vitamin A (10,000-25,000 IU/d) supplementation is instituted if an elevated prothrombin time suggests vitamin K depletion.
• Symptomatic treatment and treatment of complications

Consultations

Patients who present with advanced complications of abetalipoproteinemia (ABL) or familial hypobetalipoproteinemia (FHBL), as well as the patients' first-degree relatives, require a comprehensive evaluation for the diagnosis and management of these conditions and for genetic counseling.^{[4 ]}Expertise from the following consultants may be needed:

• Lipidologist - Patients with ABL or FHBL may require an extensive and time-consuming assessment, including genetic studies and chromosomal analyses. A lipidologist at a major center specializing in the disorders of lipid metabolism is the most appropriate consultant to involve from the start.
• Gastroenterologist - In patients with malabsorption syndrome, a thorough assessment by a gastroenterologist is necessary to exclude the many other common causes of this condition.
• Hepatologist - Patients presenting with transaminase elevation and hepatic enlargement may require specialized evaluation by a liver specialist.
• Ophthalmologist - Patients require assessment of any visual disturbance by an ophthalmologist. They also may need monitoring and periodic follow-up assessments for the development of retinal degeneration.
• Neurologist - A complete neurologic evaluation is necessary in each patient. Patients, particularly those who present with gait disturbances or ataxia, need a thorough evaluation and subsequent monitoring of any spinocerebellar degeneration.
• Nutritionist - A nutritionist must carefully evaluate the diets of patients with ABL or FHBL and suggest appropriate modifications.

Diet

• A low-fat diet, especially a reduction in the intake of long-chain fatty acids to less than 15 g per day, may alleviate intestinal symptoms.
• Oral supplementation of fat-soluble vitamins (ie, A, D, E, K) is needed.
• Supplementation of vitamin E (alpha tocopherol in high doses) may prevent progression and may even reverse some of the stigmata of spinocerebellar degeneration. However, no randomized or case-controlled study is available to support this intervention.

Activity

• No particular restriction in activity is recommended. Patients should be as active as dictated by their general health.
• In patients with spinocerebellar degeneration or ataxia, only well-tolerated and supervised activity should be advised. Such patients may benefit from orthotic devices.

Medication

Abetalipoproteinemia (ABL) and familial hypobetalipoproteinemia (FHBL) have no specific medical therapy other than vitamin supplementation, particularly high doses of vitamin E. Symptomatic medications for diarrhea and treatment of the cause of malabsorption may be needed. Dietary treatment related to ABL and FHBL is quite rigorous.

Vitamins

High-dose vitamin E therapy is used to raise tissue levels of tocopherol and to prevent the development of neurologic sequelae.

Alpha tocopherol, vitamin E (Vita-Plus E Softgels, Vitec, Aquasol E)

Vitamin E protects polyunsaturated fatty acids in membranes from attack by free radicals and protects red blood cells against hemolysis.

Dosing

Adult

100-300 mg/kg/d PO in divided doses
Heterozygous FHBL: 400-800 mg/d

Pediatric

Not established but should be strongly considered

Interactions

Mineral oil decreases absorption of vitamin E; vitamin E delays absorption of iron and increases effects of anticoagulants

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Large doses may induce vitamin K deficiency or necrotizing enterocolitis

Vitamin A (Del-Vi-A, Palmitate-A 5000)

Cofactor in many biochemical processes.

Dosing

Adult

10,000-25,000 IU/d PO

Pediatric

Not established

Interactions

None reported

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

A - Fetal risk not revealed in controlled studies in humans

X - Contraindicated; benefit does not outweigh risk

Precautions

Monitor for toxicity if dose >25,000 U/d

Follow-up

Further Inpatient Care

• Infants who present with failure to thrive may require additional monitoring and therapy in the hospital. This therapy may include the following:
  • Parenteral vitamin supplementation
  • Electrolyte and nutrient supplementation
• Patients with spinocerebellar degeneration and severe gait disturbances may need supportive measures. They may also need orthotic appliances.
• Visual assessment and therapy are indicated for retinal degeneration.

Further Outpatient Care

• Diet low in long-chain fatty acids
• Antidiarrheal medication as needed
• High-dose fat-soluble vitamin supplementation, particularly vitamin E

Inpatient & Outpatient Medications

• Vitamin E (alpha tocopherol)
• Vitamin A
• Vitamin K if prothrombin time is prolonged

Transfer

• Transfer is rarely required for patients who are finally identified as having abetalipoproteinemia (ABL) or familial hypobetalipoproteinemia (FHBL).
• Patients with advanced spinocerebellar degeneration who are unable to walk may occasionally require transfer to a tertiary care facility. Any safe method of transfer is adequate for these patients.

Deterrence/Prevention

• Abetalipoproteinemia (ABL) and familial hypobetalipoproteinemia (FHBL) are inherited disorders caused by genetic mutations.
• Obligate heterozygotes (ie, parents or offspring of homozygote patients) and possible heterozygotes (ie, siblings) should be informed that if their spouse has a very low plasma cholesterol level, the possibility exists that their children could have homozygous or compound heterozygous hypobetalipoproteinemia. Such persons should be referred to a genetic counselor at a lipid clinic.^{[4 ]}

Complications

• Gastrointestinal
  • Steatorrhea
  • Malabsorption of fat-soluble vitamins (ie, vitamins A, D, E, and/or K)
  • Steatorrhea-induced calcium malabsorption (may lead to rickets)
• Ophthalmologic
  • Ophthalmoplegia
  • Retinal degeneration
• Neurologic - Spinocellular degeneration
• Hematologic - Acanthocytosis

Prognosis

• Prognosis is reasonably good for most patients who are diagnosed early.
• Patients with prolonged vitamin deficiency, especially of vitamin E, may develop very limiting ataxia and gait disturbances.
• Some patients may develop retinal degeneration and blindness.

Patient Education

• Educating patients about the implications of their disease is of paramount importance. They should be counseled about the possible long-term complications, including blindness and gait disturbances. The need for periodic monitoring should be emphasized.
• Genetic counseling is needed for patients and their first-degree relatives.^{[4 ]}
• Nutritional counseling should include dietary recommendations for a low-fat diet (low in long-chain fatty acids) and advice to take prescribed vitamins as directed.
• For excellent patient education resources, visit eMedicine's Cholesterol Center. Also, see the eMedicine's patient education articles Cholesterol and Children and Understanding Your Cholesterol Level.

Miscellaneous

Medicolegal Pitfalls

• The diagnosis of abetalipoproteinemia (ABL) or familial hypobetalipoproteinemia (FHBL) must be considered in infants and children presenting with malabsorption syndromes. Failure to recognize the syndrome may result in long-term vitamin E deficiency and neurologic sequelae, which may have legal consequences for the health care providers.

Special Concerns

• Genetic issues pertaining to abetalipoproteinemia (ABL) or familial hypobetalipoproteinemia (FHBL) should be addressed with patients and their first-degree relatives.

References

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Keywords

low LDL cholesterol, cholesterol, LDL, LDL cholesterol, ABL, abetalipoproteinemia, hypobetalipoproteinemia, cholesterol levels, good cholesterol, triglyceride, triglycerides, lipoprotein, lipoproteins, apolipoprotein, Bassen-Kornzweig syndrome, HBL, familial hypobetalipoproteinemia, FHBL, FH-beta, low low-density lipoprotein cholesterol, Anderson disease, Anderson's disease

chylomicron retention disease, chylomicron-retention disease, lipoprotein metabolism dysfunction, lipoprotein metabolism disorder, fat malabsorption, spinocerebellar degeneration, acanthocytosis, acanthocytic red blood cells, pigmented retinopathy, malabsorption syndrome, vitamin E deficiency, vitamin deficiency, failure to thrive, ataxia, steatorrhea, retinal degeneration, blindness, spinocellular degeneration, retinitis pigmentosa

Contributor Information and Disclosures

Author

Vibhuti N Singh, MD, MPH, FACC, FSCAI, Director, Suncoast Cardiovascular Center; Chair, Cardiology Division and Cath Labs, Department of Medicine, Bayfront Medical Center; Clinical Assistant Professor, Division of Cardiology, University of South Florida College of Medicine
Vibhuti N Singh, MD, MPH, FACC, FSCAI is a member of the following medical societies: American College of Cardiology, American College of Physicians, American Heart Association, American Medical Association, and Florida Medical Association
Disclosure: Nothing to disclose.

Coauthor(s)

Elena Citkowitz, MD, PhD, FACP, Clinical Professor of Medicine, Yale University School of Medicine; Director, Cholesterol Management Center, Director, Cardiac Rehabilitation, Department of Medicine, Hospital of St Raphael
Elena Citkowitz, MD, PhD, FACP is a member of the following medical societies: American College of Physicians, American Heart Association, National Lipid Association, and Sigma Xi
Disclosure: Nothing to disclose.

Medical Editor

Udaya M Kabadi, MD, Professor, Department of Medicine, University of Iowa College of Medicine
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Yoram Shenker, MD, Chief of Endocrinology Section, Veterans Affairs Medical Center of Madison; Interim Chief, Associate Professor, Department of Internal Medicine, Section of Endocrinology, Diabetes and Metabolism, University of Wisconsin at Madison
Yoram Shenker, MD is a member of the following medical societies: American Heart Association, Central Society for Clinical Research, and Endocrine Society
Disclosure: Nothing to disclose.

CME Editor

Mark Cooper, MBBS, PhD, FRACP, Head, Diabetes & Metabolism Division, Baker Heart Research Institute, Professor of Medicine, Monash University
Disclosure: Nothing to disclose.

Chief Editor

George T Griffing, MD, Professor of Medicine, St Louis University School of Medicine
George T Griffing, MD is a member of the following medical societies: American Association for the Advancement of Science, American College of Medical Practice Executives, American College of Physician Executives, American College of Physicians, American Diabetes Association, American Federation for Medical Research, American Heart Association, Central Society for Clinical Research, Endocrine Society, International Society for Clinical Densitometry, and Southern Society for Clinical Investigation
Disclosure: Nothing to disclose.

Related eMedicine topics:
Acanthocytosis
Low HDL Cholesterol (Hypoalphalipoproteinemia)
Malabsorption
Malabsorption Syndromes
Neuroacanthocytosis
Pediatric Lipid Disorders in Clinical Practice
Retinitis Pigmentosa
Vitamin E Deficiency

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