Newborn Screening for Inherited Metabolic Disease

Abstract

Routine screening of all newborns for inherited disorders began in the 1960s after Horst Bickel had established an effective dietary therapy for phenylketonuria (PKU) and Robert Guthrie introduced a simple bacterial inhibition assay to detect elevated concentrations of phenylalanine in dried blood spots, a type of specimen universally known as the “Guthrie card.” Over time newborn screening was extended to several other treatable metabolic and endocrine disorders including galactosemia, maple syrup urine disease, biotinidase deficiency, hypothyroidism, congenital adrenal hyperplasia, and hemoglobinopathies. Beginning in the late 1990s, the scope of newborn screening has leaped forward exponentially by the introduction of acylcarnitine and amino acid analysis in Guthrie cards by tandem mass spectrometry (MS/MS). This technology has been used in biochemical genetics laboratories for the detection and analysis of acylcarnitines since the 1980s and has become amenable to newborn screening because of the development of automated, high-throughput techniques of sample preparation (typically to butyl esters derivatives) and injection into the instrument, as well as simultaneous quantitative analysis of amino acids and acylcarnitines under 2 min per sample. Amino acids are the building blocks of proteins. Acylcarnitines are formed from free carnitine and acyl-CoA moieties derived from fatty acids and organic acids (which may have been derived from amino acids) through the action of one of several carnitine-acyl-CoA transferases. This multiplex platform therefore enables the concurrent detection of disorders of amino acid, fatty acid, and organic acid intermediary metabolism and thus several of the most prevalent treatable inborn errors of metabolism. The concentrations of amino acids and acylcarnitine species fluctuate in response to many possible metabolic defects leading to complex profiles with more than 60 informative markers that require various degrees of differential diagnosis. In other words, the significant progress achieved at the analytical level has no remedy, or substitute, for the inevitable complexity of post-analytical interpretation. Additional MS/MS applications have been proposed for newborn screening, most notably several enzyme assays for lysosomal storage disorders, and lysophosphatidylcholines for X-adrenoleukodystrophy.