What is the optimal clinical plan to initiate leucovorin (folinic acid) in a young, non‑verbal child with autism spectrum disorder when parents request treatment and the folate‑receptor autoantibody (FRAT) test is unavailable?

Clinical Plan for Initiating Leucovorin in a Young Non-Verbal Child with ASD When FRAT Testing is Unavailable

Given the high prevalence of folate receptor autoantibodies (FRAAs) in children with ASD (71-75%) and the demonstrated safety and efficacy of leucovorin treatment, empirical treatment with oral leucovorin calcium at 2 mg/kg/day (maximum 50 mg/day) is a reasonable and non-invasive approach when FRAT testing is unavailable, particularly in this young non-verbal child who represents a more severely affected phenotype. 1, 2

Rationale for Empirical Treatment

• High baseline probability: Children with ASD have a 71% prevalence of FRAAs without significant variation across studies, making them 19.03-fold more likely to be positive compared to typically developing children. 3

• Non-verbal status increases likelihood: The child's non-verbal presentation suggests more severe ASD, and cerebral folate deficiency (CFD) has been associated with more complex ASD presentations. 4, 3

• Safety profile supports empirical use: The most recent high-quality randomized controlled trial (2024) demonstrated that leucovorin is safe with no adverse reactions reported, though other studies note mild adverse effects including aggression (9.5%), excitement/agitation (11.7%), insomnia (8.5%), headache (4.9%), and increased tantrums (6.2%). 2, 3

Pre-Treatment Evaluation

Before initiating leucovorin, complete the following assessments:

• Baseline autism severity measurement: Administer the Childhood Autism Rating Scale (CARS) to establish baseline severity for monitoring treatment response. 2

• Behavioral assessment: Complete the Child Behavior Checklist (CBCL) to quantify baseline behavioral problems, particularly internalizing symptoms. 2

• Communication evaluation: Document current receptive and expressive language abilities, even if minimal, to track improvements in verbal communication. 1

• Rule out alternative causes: Ensure hearing has been formally assessed with audiogram, as hearing loss can mimic ASD symptoms and must be excluded. 5, 6

• Genetic workup: If not already completed, order chromosomal microarray and fragile X testing as first-tier genetic evaluation, since 38% of children with ASD have CFD and genetic abnormalities may coexist. 4, 3

Treatment Protocol

Dosing regimen:

• Start oral leucovorin calcium (folinic acid) at 2 mg/kg/day, with a maximum dose of 50 mg/day. 2, 1
• This dosing is based on the most recent 2024 RCT and multiple prior studies demonstrating efficacy at this dose. 2, 3

Concurrent standard care:

• Continue intensive behavioral interventions, particularly Applied Behavior Analysis (ABA) and sensory integration therapy, as these remain first-line treatment for ASD per American Academy of Child and Adolescent Psychiatry guidelines. 4, 5, 2
• Leucovorin is an adjunctive treatment, not a replacement for behavioral interventions. 4, 5

Monitoring and Response Assessment

Timeline for assessment:

• Evaluate treatment response at 4 months initially, as significant improvements in verbal communication, receptive/expressive language, attention, and stereotypical behavior have been demonstrated by this timepoint. 1
• Continue monitoring through 24 weeks (6 months) for maximal benefit assessment, as the 2024 RCT demonstrated continued improvement at this interval. 2

Specific outcomes to monitor:

• CARS score changes: The 2024 RCT showed a mean improvement of 3.6 points in the leucovorin group versus 2.4 in placebo (p < 0.001). 2
• Communication improvements: Look for gains in verbal communication, receptive language, and expressive language with medium-to-large effect sizes. 3, 1
• Behavioral changes: Monitor CBCL total score and internalizing score, with expected improvements of approximately 19.7 and 15.4 points respectively based on RCT data. 2
• Core ASD symptoms: Assess attention and stereotypical behaviors, which showed significant improvement in controlled studies. 3, 1

Response expectations:

• Approximately one-third of treated children demonstrate moderate to much improvement overall. 1
• In the 2024 RCT, 67% showed improvement in overall ASD symptoms, 58% in irritability, and significant improvements in communication domains. 2, 3

Addressing Parental Concerns About FRAT Testing

Explain the evidence-based rationale:

• The 2024 RCT found that while improvement was more pronounced in children with high-titer FRAAs (p = 0.03), children without high-titer antibodies also showed improvement, though less dramatic. 2
• The pooled prevalence of CFD in ASD is 38%, with 83% of CFD cases attributed to FRAAs, making empirical treatment reasonable given the high pre-test probability. 3

Consider delayed testing:

• If FRAT testing becomes available later, it can help predict magnitude of response but should not delay treatment initiation given the safety profile and potential benefits during this critical developmental window. 2, 1
• Serum FRAA concentrations significantly correlate with cerebrospinal fluid 5-methyltetrahydrofolate concentrations, validating the test's utility when available. 1

Safety Monitoring

Adverse effect surveillance:

• Monitor specifically for aggression, excitement/agitation, insomnia, headache, and increased tantrums, which are the most common mild adverse effects. 3
• The 2024 RCT reported no adverse reactions, but meta-analysis of multiple studies shows these effects occur in 4.9-11.7% of patients. 2, 3
• Discontinue if significant adverse effects emerge, though the overall incidence is low and effects are generally mild. 1

Common Pitfalls to Avoid

• Delaying treatment pending FRAT results: Given the 71-75% prevalence of FRAAs in ASD and excellent safety profile, waiting for testing delays potentially beneficial treatment during a critical developmental period. 3, 1

• Using leucovorin as monotherapy: Leucovorin must be combined with intensive behavioral interventions (ABA), as behavioral therapy remains the evidence-based first-line treatment per AACAP guidelines. 4, 5, 2

• Inadequate monitoring duration: Assess response for at least 4-6 months, as improvements may be gradual and continue to accrue over this timeframe. 2, 1

• Failing to establish baseline measurements: Without baseline CARS and CBCL scores, quantifying treatment response becomes subjective and unreliable. 2

• Overlooking comorbidities: Screen for ADHD, anxiety, and other psychiatric comorbidities that affect 75% of children with ASD and may require additional targeted treatment. 6