With over 50 different disorders and a combined incidence of up to 1/3000 births, lysosomal storage diseases (LSDs) constitute a major public health problem and place an enormous burden on affected individuals and their families. Many factors make LSD diagnosis difficult, including phenotype and penetrance variability, shared signs and symptoms, and problems inherent to biochemical diagnosis. Developing a powerful diagnostic tool could mitigate the protracted diagnostic process for these families, lead to better outcomes for current and proposed therapies, and provide the basis for more appropriate genetic counseling.

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is the most common inherited defect in the mitochondrial fatty acid oxidation pathway, resulting in significant morbidity and mortality in undiagnosed patients.

This method will allow the determination of bound copper to low relative molecular mass compounds in milk. The milk whey obtained by ultracentrifugation was submitted to fractionation by size exclusion chromatography (SEC) on a TSK-Gel2000 (Toso Haas) column with a mobile phase of 0.2 M NH₄NO₃ + NH₃, pH 6.7. Fractions of effluent corresponding to the protein peaks were collected and the copper content was determined by ETAAS. The method was sensitive (LOD 0.4 μg l⁻¹ and LOQ 1.5 μg l⁻¹ in the fraction; LOQ 7.5–22.5 μg l⁻¹ referred to the milk sample and depended on fraction volume) and precise (RSD ± 10%). Media sample recoveries from the column were 101.2%. Cu was predominantly present in fractions corresponding to relative molecular mass 76 and 15 kDa of breast milk while copper was mostly found in fractions corresponding to 14 and 38 kDa of cow’s milk-based infant formulae; moreover, copper was eluted in the relative molecular mass region <6 kDa.

A method to determine the selenium distribution in milk whey fractions was developed. After milk whey preconcentration by ultrafiltration, selenium in the protein fractions was separated by size exclusion chromatography (SEC) and determined by electrothermal atomic absorption spectroscopy (ETAAS) using a sampling procedure based on fraction collection, fraction preconcentration by ultrafiltration and introduction into the furnace after digestion, hydride generation and hydride preconcentration. The digestion and reduction conditions of the milk whey fractions obtained by SEC were studied. The hydride generation parameters and preconcentration into an iridium coated graphite tube using ETAAS with a Zeeman background correction were optimised. The method was applied to six infant formula milks and selenium was found in three fractions of cow-based infant formulas: 40 kDa, >160 kDa and mostly in the <10 kDa fraction.