Congenital bile acid synthesis defect type 1

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Congenital bile acid synthesis defect type 1 is a disorder characterized by cholestasis, a condition that impairs the production and release of a digestive fluid called bile from liver cells. Bile is used during digestion to absorb fats and fat-soluble vitamins, such as vitamins A, D, E, and K. People with congenital bile acid synthesis defect type 1 cannot produce (synthesize) bile acids, which are a component of bile that stimulate bile flow and help it absorb fats and fat-soluble vitamins. As a result, an abnormal form of bile is produced.

The signs and symptoms of congenital bile acid synthesis defect type 1 often develop during the first weeks of life, but they can begin anytime from infancy into adulthood. Affected infants often have difficulty gaining weight and growing at the expected rate (faltering weight). They may also have yellowing of the skin and eyes (jaundice) due to impaired bile flow and a buildup of partially formed bile. Excess fat in the feces (steatorrhea) is an additional feature of congenital bile acid synthesis defect type 1. As the condition progresses, affected individuals can develop liver abnormalities including an enlarged liver (hepatomegaly), inflammation, or chronic liver disease (cirrhosis). The spleen may also become enlarged (splenomegaly). The inability to absorb certain fat-soluble vitamins (vitamin D in particular) can result in softening and weakening of the bones (rickets) in some individuals.

If left untreated, congenital bile acid synthesis defect type 1 often leads to cirrhosis and death in childhood.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the HSD3B7 gene cause congenital bile acid synthesis defect type 1. The HSD3B7 gene provides instructions for making an enzyme called 3 beta-hydroxysteroid dehydrogenase type 7 (3β-HSD7). This enzyme is found in liver cells that produce bile acids. Bile acids are produced from cholesterol in a multi-step process. The 3β-HSD7 enzyme is responsible for the second step in that process, which converts 7alpha(α)-hydroxycholesterol to 7α-hydroxy-4-cholesten-3-one.

HSD3B7 gene mutations result in a 3β-HSD7 enzyme with little or no function. Without enough functional 3β-HSD7 enzyme, the conversion of 7α-hydroxycholesterol to 7α-hydroxy-4-cholesten-3-one is impaired. The 7α-hydroxycholesterol instead gets converted into abnormal bile acid compounds that cannot be transported out of the liver into the intestine, where the bile acids are needed to digest fats. As a result, cholesterol and other fats build up in the liver and fat-soluble vitamins are not absorbed, which contribute to the signs and symptoms of congenital bile acid synthesis defect type 1.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

The prevalence of congenital bile acid synthesis defect type 1 is unknown; however, it is the most common of all the congenital defects of bile acid synthesis. Together, these conditions are thought to have a prevalence of 1 to 9 per million people.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Biliary tract abnormality · Very frequent (99-80%)

An abnormality of the biliary tree.

Elevated circulating hepatic transaminase concentration · Very frequent (99-80%)

Elevations of the levels of SGOT and SGPT in the serum. SGOT (serum glutamic oxaloacetic transaminase) and SGPT (serum glutamic pyruvic transaminase) are transaminases primarily found in the liver and heart and are released into the bloodstream as the result of liver or heart damage. SGOT and SGPT are used clinically mainly as markers of liver damage.

Failure to thrive · Very frequent (99-80%)

Failure to thrive (FTT) refers to a child whose physical growth is substantially below the norm.

Hepatomegaly · Very frequent (99-80%)

Abnormally increased size of the liver.

Jaundice · Very frequent (99-80%)

Yellow pigmentation of the skin due to bilirubin, which in turn is the result of increased bilirubin concentration in the bloodstream.

Malabsorption · Very frequent (99-80%)

Impaired ability to absorb one or more nutrients from the intestine.

Neonatal cholestatic liver disease · Very frequent (99-80%)

Abnormality of coagulation · Frequent (79-30%)

An abnormality of the process of blood coagulation. That is, altered ability or inability of the blood to clot.

Other findings in the same source

From: Orphanet

Additional reported features include Gastrointestinal hemorrhage (Frequent (79-30%)); Splenomegaly (Frequent (79-30%)); Abnormal bleeding (Occasional (29-5%)); Cirrhosis (Occasional (29-5%)); Nyctalopia (Occasional (29-5%)); Osteoporosis (Occasional (29-5%)); Peripheral neuropathy (Occasional (29-5%)); Pruritus (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Congenital bile acid synthesis defect type 1 is Hepatology, with a hepatologist / gastroenterologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• What is known about the cause and extent of liver involvement?
• Which medicines, supplements or exposures should be reviewed?
• What follow-up is appropriate for the specific diagnosis and stage?

Treatment discussions and follow-up

Where the source describes treatments, these are an overview of possible care, not a prescription for an individual. Ask which option applies to the confirmed diagnosis, what benefit is expected, what adverse effects to watch for and how progress will be assessed. Availability, approvals and local practice can differ from the country described in the source.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.