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ACAD9 deficiency

 ACAD9 deficiency



Overview

ACAD9 deficiency is a rare, autosomal recessive metabolic disorder that impairs mitochondrial function, leading to reduced energy production. It primarily causes severe muscle weakness, hypertrophic cardiomyopathy (enlarged heart), and lactic acidosis. Often presenting in infancy, it can be fatal but may respond to high-dose Riboflavin therapy.

Symptoms

Muscle Issues (Myopathy): Low muscle tone (hypotonia), muscle weakness (myopathy), and exercise intolerance (fatigue).

Cardiac Issues (Cardiomyopathy): Enlarged and weakened heart muscle (hypertrophic cardiomyopathy is common), rhythm abnormalities, and potential heart failure. Neurological Issues: Intellectual disability, developmental delays, seizures, and sometimes movement disorders.

Metabolic Crisis: Acute symptoms can include severe lactic acidosis, liver dysfunction, vomiting, and failure to thrive in infants.

Other Symptoms: Shortness of breath, fatigue, and in some cases, Leigh's syndrome (a severe progressive neurodegenerative disease).

Causes

Autosomal Recessive Inheritance: Both copies of the ACAD9 gene in each cell must have mutations for a person to be affected. Parents are generally unaffected carriers.

Defective Complex I Assembly: The primary cause of symptoms is the failure to properly assemble complex I within the mitochondria, leading to impaired oxidative phosphorylation (the process of producing cell energy).Impaired Fatty Acid Oxidation: Some mutations also disrupt the enzyme’s role in breaking down long-chain fatty acids, causing further energy deficits.

Mutation Impact: At least 30 mutations have been identified, most changing single amino acids (missense mutations), which can lead to severe structural instability of the enzyme.

Risk Factors

Genetic Inheritance: Autosomal recessive. Carriers (parents) are asymptomatic, while each child of carrier parents has a 25% (1 in 4) chance of inheriting the condition

.Disease Severity Factors: The type of mutation influences the severity. Mutations impacting both enzyme stability and Complex I assembly (as described by MedlinePlus Genetics) often present more severely than those affecting only Complex I.

Clinical Indicators: Key indicators that prompt testing include early-onset hypertrophic cardiomyopathy (weakened heart), lactic acidosis, muscle weakness (myopathy), and developmental delays.

Age of Onset: Severe cases typically manifest in infancy with rapid onset, while milder cases can appear later in childhood, sometimes associated with metabolic triggers.

Complication

Cardiac Involvement: Hypertrophic cardiomyopathy is a common, often fatal complication, with some presenting with severe neonatal progression of cardiomegaly.

Neurological Dysfunction: Encephalopathy and severe intellectual disability are frequent.

Metabolic Crisis: Severe lactic acidosis, hypoglycemia, and Reye-like syndrome (vomiting, confusion) can occur.

Neuromuscular Issues: Severe hypotonia (low muscle tone), weakness, and exercise intolerance are common, especially in survivors.

Other Organ Involvement: Hepatic dysfunction and kidney problems have been reported in rare cases.

High Risk of Death: Severely affected individuals often experience fatal outcomes in infancy or early childhood.

Diagnosis

Genetic Testing (Gold Standard): Next-generation sequencing (NGS) of the ACAD9 gene, or comprehensive whole-exome sequencing, is necessary to identify pathogenic variants.

Biochemical Testing: Elevated plasma lactate levels are commonly seen. Acylcarnitine profile analysis often reveals elevated C4- and C16-carnitine species.

Enzyme Activity Assays: Measurements can show a decrease in complex I activity in mitochondrial respiratory chain studies.

Clinical Evaluation: Diagnosis is often suspected in cases of unexplained early-onset heart failure (hypertrophic cardiomyopathy), severe muscle weakness, and liver dysfunction

Treatment

Riboflavin (Vitamin B2) Therapy: High-dose riboflavin (\(100 \text{ mg/kg/day}\) or similar) is often effective in roughly 65% of cases. It works by enhancing the assembly of the ACAD9 protein.

Bezafibrate and Nicotinamide Riboside: Recent studies suggest these may provide stabilization for cardiomyopathy and help manage metabolic acidosis, although some patients may still experience progression.

Cofactor Support: Supplementation with Coenzyme Q10 and sodium pyruvate can be added to improve energy metabolism.

Symptom Management: Treatment includes addressing specific symptoms like cardiomyopathy with appropriate medications (e.g., beta-blockers).Monitoring and Lifelong Care:

Type of Doctor Department : Metabolic Specialist/Biochemical Geneticist , Pediatrician or Pediatric Neurologist


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