Comprehensive Creatine and Guanidinoacetate Determination

Casandra

Casandra Test Code BA90271Version 1 (DRAFT)

Performing Lab

Lab Baylor GeneticsLab Test ID 4015CPT Codes 82540, 82570, 83789

Comprehensive Creatine and Guanidinoacetate Determination

Clinical Use

Use

This test provides quantitative analysis of creatine and guanidinoacetate in plasma and urine; it is useful for evaluating patients with clinical suspicion of inborn errors of creatine metabolism, such as GAMT deficiency, AGAT deficiency, and creatine transporter deficiency. Creatine deficiency syndromes are characterized by intellectual disability, cognitive speech disturbances, seizures, and movement disorders, often marked by cerebral creatine depletion detectable by magnetic resonance spectroscopy. Elevated GAA levels in plasma or urine are characteristic of GAMT deficiency, while low GAA and normal-low creatine concentrations are indicative of AGAT deficiency. Male CTD patients often exhibit an increased urine creatine-to-creatinine ratio. Both syndromes can manifest in patients with developmental delays and seizures.

Special Instructions

Indications for Testing include patients with a history of seizures, global developmental delay, failure to thrive, speech delay, and/or behavioral difficulties. How this disease is inherited involves that GAMT deficiency and AGAT deficiency are both inherited in an autosomal recessive manner, needing both parents to be carriers for at-risk conditions. CTD is inherited in an X-linked manner, involving pathogenic variants in the SLC6A8 gene. Female carriers have a 50% chance of passing down the variant to children.

Limitations

This test relies on the accurate collection and preservation of plasma and urine specimens. Timing and storage conditions are critical for valid results. False negatives may occur if the specimens are not properly handled or if the patient has atypical presentation of the conditions. Additionally, while this analysis is useful for detecting creatine metabolism disorders, it may not completely rule out other metabolic or genetic disorders.

Test Details