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Disease Profile

Holocarboxylase synthetase deficiency

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.


US Estimated

Europe Estimated

Age of onset






Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

Early-onset multiple carboxylase deficiency; Neonatal multiple carboxylase deficiency


Congenital and Genetic Diseases; Newborn Screening; Skin Diseases


The following summary is from Orphanet, a European reference portal for information on rare diseases and orphan drugs.

Orpha Number: 79242

A life-threatening early-onset form of multiple carboxylase deficiency, an inborn error of biotin metabolism, that, if untreated, is characterized by vomiting, tachypnea, irritability, lethargy, exfoliative dermatitis, and seizures that can worsen to coma.

The exact prevalence of HCSD is unknown, but the condition is one of the rarest inborn errors of metabolism. Annual incidence is estimated to be less than 1/200,000 live births.

Clinical description
Clinical onset is usually within hours, days or weeks of birth. Individuals with the disorder usually exhibit poor appetite, vomiting, lethargy, irritability, hypotonia and exfoliative dermatitis. Metabolically, they have ketolactic acidosis, organic acidemia (-uria) and hyperammonemia. Without treatment, affected infants may progress to intractable seizures, cerebral edema and coma. These children often develop growth and developmental delays.

Holocarboxylase synthetase deficiency is caused by mutations in the HLCS gene (21q22.1) resulting in reduced HCS activity. This enzyme is important in covalent binding of biotin to the various biotin-dependent carboxylases that require the vitamin for activity. Failure to attach the biotin results in multiple carboxylase deficiency and accumulation of various, specific abnormal organic acids.

Diagnostic methods
Some affected individuals are identified through newborn screening by demonstration of abnormal organic acids, consistent with multiple carboxyalse deficiency. Diagnosis is based on clinical signs and typical organic acid abnormalities. Confirmational testing can be performed by demonstrating deficient HCS activity in leukocytes or fibroblast extracts or by mutation analysis.

Differential diagnosis
Conditions to be considered in the differential diagnosis based on organic acids include biotinidase deficiency (see this term) and isolated carboxyalse deficiencies; based on hyperammonemia, include urea cycle defects (see this term); and based on neurological compromise and seizures in the neonatal period, include sepsis and other inborn errors of metabolism.

Antenatal diagnosis
Prenatal diagnosis can be performed by organic acid analysis by stable isotope dilution techniques in amniotic fluid, enzymatic determination of HCS activity in amniocytes, or mutation analysis on DNA from chorionic villus biopsy or amniocentesis.

Genetic counseling
HCS deficiency is inherited as an autosomal recessive trait. Genetic counseling is available to families who have children with the disorder. Siblings of affected children are unlikely to have the disorder or they would have developed symptoms, but they may be carriers.

Management and treatment
The primary treatment for HCS deficiency is free biotin supplementation which can improve the clinical status of symptomatic individuals with the enzyme deficiency and prevent some or all symptoms from developing in asymptomatic individuals with the disorder. Treatment should be started as soon as possible after diagnosis and must be continued lifelong. Affected individuals should be monitored for later-onset complications and for compliance with therapy. Timely and ongoing treatment makes it possible to reduce symptoms considerably, although some patients develop complications despite appropriate treatment often requiring higher doses of biotin.

In the absence of early diagnosis and treatment, mortality is high. Morbidity in surviving affected individuals depends on the time of diagnosis and on the degree of damage related to metabolic crises.

Visit the Orphanet disease page for more resources.


This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
80%-99% of people have these symptoms
Growth delay
Delayed growth
Growth deficiency
Growth failure
Growth retardation
Poor growth
Retarded growth

[ more ]

Muscular hypotonia
Low or weak muscle tone
Nausea and vomiting
Perioral eczema
Eczema around the mouth
Weight loss
30%-79% of people have these symptoms
High blood ammonia levels
Organic aciduria
Respiratory distress
Breathing difficulties
Difficulty breathing

[ more ]

Increased respiratory rate or depth of breathing
5%-29% of people have these symptoms
Hair loss
Desquamation of skin soon after birth
Low platelet count
Percent of people who have these symptoms is not available through HPO
Autosomal recessive inheritance
Feeding difficulties in infancy
Generalized hypotonia
Decreased muscle tone
Low muscle tone

[ more ]

Global developmental delay
Rapid breathing
Metabolic acidosis
Skin rash
Throwing up


Making a diagnosis for a genetic or rare disease can often be challenging. Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis. The following resources provide information relating to diagnosis and testing for this condition. If you have questions about getting a diagnosis, you should contact a healthcare professional.

Testing Resources

  • The Genetic Testing Registry (GTR) provides information about the genetic tests for this condition. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.

Newborn Screening

  • An ACTion (ACT) sheet is available for this condition that describes the short-term actions a health professional should follow when an infant has a positive newborn screening result. ACT sheets were developed by experts in collaboration with the American College of Medical Genetics.
  • An Algorithm flowchart is available for this condition for determining the final diagnosis in an infant with a positive newborn screening result. Algorithms are developed by experts in collaboration with the American College of Medical Genetics.
  • Baby's First Test is the nation's newborn screening education center for families and providers. This site provides information and resources about screening at the local, state, and national levels and serves as the Clearinghouse for newborn screening information.
  • National Newborn Screening and Global Resource Center (NNSGRC) provides information and resources in the area of newborn screening and genetics to benefit health professionals, the public health community, consumers and government officials.

Learn more

These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

Where to Start

  • Genetics Home Reference (GHR) contains information on Holocarboxylase synthetase deficiency. This website is maintained by the National Library of Medicine.
  • The National Organization for Rare Disorders (NORD) has a report for patients and families about this condition. NORD is a patient advocacy organization for individuals with rare diseases and the organizations that serve them.
  • The Screening, Technology And Research in Genetics (STAR-G) Project has a fact sheet on this condition, which was written specifically for families that have received a diagnosis as a result of newborn screening. This fact sheet provides general information about the condition and answers questions that are of particular concern to parents.

In-Depth Information

  • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
  • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.