Persistent elevations of alkaline phosphatase as an early indicator of GM1 gangliosidosis.

Abstract

GLB1-related disorders are autosomal recessive lysosomal diseases caused by enzymatic deficiency of β-galactosidase. Enzymatic deficiency of β-galactosidase may lead to one of two phenotypes, GM1 gangliosidosis or mucopolysaccharidosis IVB (MPS IVB). GM1 gangliosidosis is a neurodegenerative disorder with variable skeletal disease and involvement of other systems. The age of onset correlates with the extent of neurological involvement and established genotype/phenotype correlations. Mucopolysaccharidosis IVB is characterized by a skeletal dysplasia without neurological involvement. Diagnostic work-up for GLB1-related disorders includes enzyme analysis, biomarker analysis, molecular testing, and laboratory imaging studies. We report a patient who presented with persistent elevations of alkaline phosphatase (ALP) and subtle dysmorphic facial features. An initial skeletal survey at birth was unrevealing; however, a repeat at 3 months of age was abnormal with anterior beaking of the lumbar vertebrae and hemivertebrae of the lower cervical spine. Urinary glycosaminoglycan (GAG) analysis revealed a marked elevation of keratan sulfate (KS). Clinical exome sequencing revealed pathogenic heterozygous variants in GLB1, consistent with GLB1-related GM1 gangliosidosis. Our case demonstrates that persistent elevations of ALP may be an early indicator for GM1 gangliosidosis in an infant with progressive multisystem disease, indicating the need for early genetic consultation. This case also highlights the utility of repeat skeletal surveys with abnormalities detected at 3 months of age.