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2. Explanation of the reference case

The tutorial uses as a reference case, the model developed to assess the cost-effectiveness of adding Biotinidase Deficiency (BD) newborn screening (NBS) to the national NBS program in Spain, as described by Vallejo-Torres et al. (2015). The analysis takes the perspective of the Spanish National Health Service (NHS), using Quality-Adjusted Life Years (QALYs) as the measure of effectiveness.

2.1. Biotinidase deficiency

  • Nature: BD is an autosomal recessive inherited disorder where the enzyme biotinidase is defective, preventing the recycling of the vitamin biotin.
  • Forms: Categorized as profound BD (<10% of normal activity) and partial BD (10%–30% of normal activity).
  • Consequences (Untreated): Untreated profound BD can lead to severe neurologic and cutaneous symptoms including seizures, hypotonia, skin rash, alopecia, cognitive deficits, optic atrophy, and sensorineural hearing loss. Some consequences, like developmental delay, optic atrophy, and hearing loss, are generally irreversible once they occur.
  • Incidence (Galicia, Spain): Combined BD incidence was estimated at 1 in 22,540 newborns, higher than the worldwide estimate.

2.2. Interventions Compared

  1. Screening Strategy (Intervention): Universal NBS for BD, including two initial screening tests, diagnostic confirmation, and lifelong oral biotin supplementation for confirmed cases. Cases detected early and treated are assumed to remain asymptomatic.
  2. No Screening Strategy (Comparator): Cases are detected only after the onset of clinical symptoms (clinical detection), leading to complications if not treated rapidly.