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Short/Branched Chain Acyl-CoA Dehydrogenase (SBCAD) Deficiency

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Guidance for primary care clinicians receiving a positive newborn screen result

Other Names

2-methylbutyrylglycinuria

ICD-10 Coding

E71.19, Other disorders of branched-chain amino-acid metabolism

Disorder Category

Organic acidemia

Screening

Abnormal Finding

Elevated C5 acylcarnitine

Tested By

Tandem mass spectrometry

Description

Short/branched chain acyl-CoA dehydrogenase (SBCAD) deficiency is a disorder of isoleucine metabolism that is often found incidentally on newborn screening with an elevated C5 level. The clinical significance of this biochemical finding is to be determined - the majority of patients remain asymptomatic. Estimates suggest that approximately 10% of patients may develop symptoms, which can include variable onset from neonatal to early childhood with seizures, developmental delay, hypotonia, and failure to thrive. [Porta: 2019]

Clinical Characteristics

With treatment: Although there is not much information regarding treatment, some may recommend a low-protein diet and L-carnitine supplementation. However, most individuals with this condition will not require treatment, though this needs to be determined in consultation with a pediatric metabolic specialist.
Without treatment: Although most people with SBCAD deficiency do not have symptoms, some children with variants that cause severe disease may present with early-onset seizures, hypotonia, and failure to thrive. Infants/children with this condition may be susceptible to metabolic acidosis when fasting and/or during illnesses.
Gene therapy trials are in progress but are currently targeted only towards adults. Supportive Treatment: May include physical therapy, occupational therapy, speech therapy, feeding tubes, and mechanical ventilation depending on severity of symptoms.
Initial signs and symptoms of SBCAD deficiency, consistent with metabolic acidosis, may include:
  • Poor appetite
  • Lethargy
  • Irritability
  • Developmental delays
  • Poor growth
  • Hypotonia

Incidence

The incidence is unknown but very rare except in the Hmong population, whereas many as 1 out of every 250-500 is affected. Those affected by the common Hmong variant are even less likely to develop symptoms. [Porta: 2019]

Inheritance

Autosomal recessive

Primary Care Management

Next Steps After a Positive Screen

  • Contact the family and evaluate the infant for seizures, poor feeding, lethargy, and vomiting.
  • Provide emergency treatment/referral as needed.
  • Educate the family about signs/symptoms of metabolic acidosis (see above) and the need for urgent treatment if symptoms are present.

Confirming the Diagnosis

  • To confirm the diagnosis of SBCAD deficiency, work with Newborn Screening Services (see NM providers [3]).
  • Follow-up biochemical testing for suspected cases may include plasma acylcarnitine analysis to confirm the increased C5 and urine organic acids to identify 2-methylbutyrylglycine. Urine acylglycine may also be informative. Confirmation can also be made with genetic testing for ACADSB gene variants.

If the Diagnosis is Confirmed

  • For evaluation and ongoing collaborative management, consult Biochemical Genetics (Metabolics) Clinics (see NM providers [2]).
  • Educate the family regarding the signs and symptoms of metabolic acidosis and the need for urgent care when the infant becomes ill.
  • Work with the metabolic specialist for evaluation and collaborative management.

Resources

Information & Support

Related Portal Content
After a Diagnosis or Problem is Identified
Families can face a big change when their baby tests positive for a newborn condition. Find information about A New Diagnosis - You Are Not Alone; Caring for Children with Special Health Care Needs; Assistance in Choosing Providers; Partnering with Healthcare Providers; Top Ten Things to Do After a Diagnosis.

For Professionals

2-Methylbutyryl-CoA Dehydrogenase Deficiency (OMIM)
Information about clinical features, diagnosis, management, and molecular and population genetics; from Online Mendelian Inheritance in Man, authored and edited at the McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine

For Parents and Patients

Baby's First Test: 2-Methylbutyrylglycinuria
Information about early signs, follow-up testing, treatment, accessing care, and expected outcomes. Provides links to support services.

2MBC (2-Methylbutyryl-CoA Dehydrogenase Deficiency) (STAR-G)
Very detailed information for families, including description, causes, outcomes, genetic testing, incidence, and more from the Screening, Technology And Research in Genetics Project, begun by the Hawaii Department of Health and now maintained by the Western States Regional Genetics Network.

2-Methylbutyryl-CoA Dehydrogenase Deficiency (GARD)
Includes information about symptoms, inheritance, diagnosis, finding a specialist, related diseases, and support organizations; Genetic and Rare Diseases Information Center of the National Center for Advancing Translational Sciences.

Organic Acidemia Association (OAA)
A nonprofit organization that provides information, support, events, connections with other parents, a discussion board, and nutrition and recipe ideas.

Tools

NM ACT Sheet for Elevated C5 Acylcarnitine (ACMG) (PDF Document 117 KB)
Provides recommendations for clinical and laboratory follow-up of the newborn with out-of-range screening results, along with other resources for clinicians and families; American College of Medical Genetics.

Confirmatory Algorithm for Elevated C5 (ACMG) (PDF Document 194 KB)
An algorithm of the basic steps involved in determining the final diagnosis of an infant with a positive newborn screen; American College of Medical Genetics.

Services for Patients & Families in New Mexico (NM)

For services not listed above, browse our Services categories or search our database.

* number of provider listings may vary by how states categorize services, whether providers are listed by organization or individual, how services are organized in the state, and other factors; Nationwide (NW) providers are generally limited to web-based services, provider locator services, and organizations that serve children from across the nation.

Helpful Articles

Porta F, Chiesa N, Martinelli D, Spada M.
Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature.
J Pediatr Endocrinol Metab. 2019;32(2):101-108. PubMed abstract

Authors & Reviewers

Initial publication: March 2021; last update/revision: November 2021
Current Authors and Reviewers:
Author: Brian J. Shayota, MD, MPH
Authoring history
2018: update: Nicola Longo, MD, Ph.D.A
2011: update: Nicola Longo, MD, Ph.D.A
2007: first version: Nicola Longo, MD, Ph.D.A
AAuthor; CAContributing Author; SASenior Author; RReviewer

Page Bibliography

Porta F, Chiesa N, Martinelli D, Spada M.
Clinical, biochemical, and molecular spectrum of short/branched-chain acyl-CoA dehydrogenase deficiency: two new cases and review of literature.
J Pediatr Endocrinol Metab. 2019;32(2):101-108. PubMed abstract