Alkaline Phosphatase and Infantile <scp>GM1</scp> Gangliosidosis: A Simple Biomarker for a Complex Disease?

GM1 gangliosidosis is a lysosomal storage disease (LSD) caused by β-galactosidase deficiency, characterized by the accumulation of gangliosides in various tissues. Among different GM1 forms (infantile form, late-infantile and juvenile form, and late-onset form), the infantile form is the most severe: despite an early clinical onset with rapid neurodegeneration, coarse face, abdominal visceromegaly and skeletal abnormalities, the diagnosis is usually delayed, given the lack of recognized early disease-specific markers. We report the case of a newborn presenting with mild edema of hands and feet, mild transient hypoalbuminemia and isolated hyperphosphatasemia at three weeks of life. The first cardiological evaluation showed mild mitral regurgitation. Despite the absence of neurological symptoms, organomegaly, or a coarse face, the turgid consistency of the limbs, together with mitral regurgitation and persistent hyperphosphatasemia, led to multiorgan investigations with discovery of bilateral cherry-red spots and a beak-shaped lumbar vertebra. The cardiological follow-up revealed a dysplastic mitral valve. In the suspicion of a lysosomal disease, biochemical investigations were planned. An altered profile of urinary oligosaccharides, along with low β-galactosidase activity in leukocytes, led to the diagnosis of infantile GM1 gangliosidosis at 3 months of age. The <i>GLB1</i> gene analysis confirmed the diagnosis. Genetic testing for GLB1 should be considered in cases of persistent hyperphosphatemia, especially if it is associated with any other clinical indicator of GM1, such as limb edema.