Hyperprolinemia in Type 2 Glutaric Aciduria and MADD-Like Profiles

Abstract

Classical neonatal-onset glutaric aciduria type 2 (MAD deficiency) is a severe disorder of mitochondrial fatty acid oxidation associated with poor survival. Secondary dysfunction of acyl-CoA dehydrogenases may result from deficiency for riboflavin transporters, leading to severe disorders that, nevertheless, are treatable by riboflavin supplementation. In the last 10 years, we identified nine newborns with biochemical features consistent with MAD deficiency, only four of whom survived past the neonatal period. A likely iatrogenic cause of riboflavin deficiency was found in two premature newborns having parenteral nutrition, one of whom recovered upon multivitamin supplementation, whereas the other died before diagnosis. Four other patients had demonstrated mutations involving ETF or ETF-DH flavoproteins, whereas the remaining three patients presumably had secondary deficiencies of unknown mechanism. Interestingly, six newborns among the seven tested for plasma amino acids had pronounced hyperprolinemia. In one case, because the initial diagnostic workup did not include organic acids and acylcarnitine profiling, clinical presentation and hyperprolinemia suggested the diagnosis. Analysis of our full cohort of >50,000 samples from >30,000 patients suggests that the proline/alanine ratio may be a good marker of MAD deficiency and could contribute to a more effective management of the treatable forms.

Fig. 1

Box plots of age-normalized levels of 21 plasma amino acids for samples from patients with primary (yellow) or presumably secondary (blue) MAD deficiency at presentation. Y-axis: age-normalized standard deviations from a hospital reference population. Amino acids are ordered from the lowest (alanine, ALA) to the highest median levels (proline, PRO) across all samples. The boxes cover the ±25th percentile from the median (horizontal line in the boxes); the dotted lines cover the ±95th percentile from the median

Fig. 2

The plasma levels of alanine (“ALA”, x-axis) and proline (“PRO”, y-axis) in micromoles/liter are shown for 53,338 samples corresponding to our complete cohort (gray). The samples collected at presentation from the patients reported in this study are shown as red (newborns with primary MADD) or blue circles (newborn with suspected secondary MADD). The equality line is blue, indicating that average reference alanine levels are greater than proline. Useful cutoffs are shown by black dashed lines and a proposed continuous cutoff by a red line (corresponding to the equation PRO = 1.4 × ALA + 140) (see text). The black ellipse represents the estimated bivariate normal distribution at alpha = 10⁻⁵