Clinical characteristics: The phenotypic spectrum of untreated glutaric acidemia type 1 (GA-1) ranges from the more common form (infantile-onset disease) to the less common form (later-onset disease – i.e., after age 6 years). Of note, the GA-1 phenotype can vary widely between untreated family members with the same genotype, primarily as a function of the age at which the first acute encephalopathic crisis occurred: three months to six years in infantile-onset GA-1 and after age six years in later-onset GA-1. Characteristically these crises result in acute bilateral striatal injury and subsequent complex movement disorders. In the era of newborn screening (NBS), the prompt initiation of treatment of asymptomatic infants detected by NBS means that most individuals who would have developed manifestations of either infantile-onset or later-onset GA-1 remain asymptomatic; however, they may be at increased risk for other manifestations (e.g., renal disease) that are becoming apparent as the understanding of the natural history of treated GA-1 continues to evolve.
Diagnosis/testing: Because the early initiation of treatment dramatically improved the outcome for persons with GA-1, an international guideline group has recommended NBS. The diagnosis of GA-1 in a proband with a positive NBS result or suggestive biochemical and/or clinical findings is confirmed by identification of biallelic pathogenic variants in GCDH or, when molecular genetic test results are uncertain, by detection of significantly reduced activity of the enzyme glutaryl-CoA dehydrogenase (GCDH) in cultured fibroblasts or leukocytes.
Management: Prevention of primary manifestations: When GA-1 is suspected during the diagnostic evaluation of a newborn with an elevated concentration of 3-OH-GA in plasma or urine, metabolic treatment should be initiated immediately. Development and evaluation of treatment plans, training and education of affected individuals and their families, and avoidance of side effects of dietary treatment (i.e., malnutrition, growth failure) require a multidisciplinary approach by experienced subspecialists from a specialized metabolic center. The main principles of treatment are to reduce lysine oxidation and enhance physiologic detoxification of glutaryl-CoA. Combined metabolic therapy includes low-lysine diet, carnitine supplementation, and emergency treatment during episodes with the goal of averting catabolism and minimizing CNS exposure to lysine and its toxic metabolic byproducts.
Surveillance: Regular evaluations by a metabolic specialist and metabolic dietician; routine evaluation of growth parameters and head circumference, developmental progress and educational needs, clinical signs and symptoms of movement disorders, biochemical parameters, and renal function (in adolescents and adults).
Agents/circumstances to avoid: Excessive dietary protein or protein malnutrition inducing catabolic state, prolonged fasting, catabolic illness (intercurrent infection; brief febrile illness post vaccination), inadequate caloric provision during other stressors (e.g., surgery or procedure requiring fasting/anesthesia).
Evaluation of relatives at risk: Testing of all at-risk sibs of any age to allow for early diagnosis and treatment. For at-risk newborn sibs when prenatal testing was not performed: in parallel with NBS either test for the familial GCDH pathogenic variants or measure urine organic acids, plasma amino acids, and acylcarnitine profile.
Pregnancy management: It is recommended that care for a pregnant woman with GA-1 be provided by a multidisciplinary team including the treating obstetrician, a metabolic physician, and a specialist metabolic dietician.
Genetic counseling: GA-1 is inherited in an autosomal recessive manner. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Once the GCDH pathogenic variants in an affected family member are known, carrier testing for at-risk relatives, prenatal testing for a pregnancy at increased risk, and preimplantation genetic testing are possible.
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