[13C]-galactose breath test in a patient with galactokinase deficiency and spastic diparesis

Abstract

Galactokinase deficiency is an inborn error of carbohydrate metabolism due to a block in the formation of galactose-1-phosphate from galactose. Although the association of galactokinase deficiency with formation of cataracts is well established, the extent of the clinical phenotype is still under investigation. We describe a 6-year-old female who was diagnosed with galactokinase deficiency due to cataract formation when she was 10 months of age and initially started on galactose-restricted diet at that time for 5 months. She developed gait abnormality at 4 years of age. Breath tests via measurement of ¹³C isotope in exhaled carbon dioxide following ¹³C-labeled galactose administration at carbon-1 and carbon-2 positions revealed oxidation rates within the normal range. The results in this patient strikingly contrast with the results of another patient with GALK1 deficiency that underwent breath testing with [1-¹⁴C]-galactose and [2-¹⁴C]-galactose. Extension of in vivo breath tests to other galactokinase patients is needed to better understand the pathophysiology of this disease.

Keywords: GALK1 deficiency; galactosemia; in vivo galactose oxidation; stable‐isotope labeled galactose.

FIGURE 1

Breath tests results in the galactokinase deficiency patient after administration of 100 mg [1‐¹³C]‐galactose or [2‐¹³C]‐galactose. A, The difference between the ratio ¹³CO₂/¹²CO₂ in the expired air after administration of the dose is given as delta over baseline. B, Cumulative percent dose of ¹³CO₂ over time is shown. C, Fractional elimination of the dose as the μmol ¹³CO₂/min/μmol dose × 10⁴ over 5 hours is shown

FIGURE 2

¹³C‐labeled plasma galactose and enrichment of ¹³C in plasma glucose after administration of [1‐¹³C]‐galactose (top panel) or [2‐¹³C]‐galactose (bottom panel) over time are shown