Child Neurology: Exaggerated dermal melanocytosis in a hypotonic infant: A harbinger of GM1 gangliosidosis

Abstract

Gangliosidoses are a group of rare lysosomal storage diseases (LySD) involving the accumulation of lipids in multiple organ systems, including the central and peripheral nervous systems. These disorders are inherited in an autosomal recessive pattern and are broadly grouped into 2 types. GM1 gangliosidoses (GM1) are due to a deficiency of the enzyme β-galactosidase, and GM2 diseases (Tay-Sachs, AB variant, and Sandhoff disease) are due to a deficiency of the enzyme β-hexosaminidase. GM1, first described biochemically by Dr. John S. O'Brien in the 1960s, is estimated to occur in 1 in 100,000–200,000 newborns.1 Despite being the first of the gangliosidoses identified as well as the most prevalent, GM1 often presents a diagnostic challenge to the child neurologist. GM1 type 1, the infantile form, is the most common and the most severe. Patients present with nonspecific neurologic features including hypotonia, sensory impairment, and developmental regression within the first year of life; thus, a broad differential diagnosis is often entertained. We report a complex case of infantile GM1 diagnosed following identification of an extensive dermal melanocytosis on physical examination. This distinguishing feature has been increasingly recognized as a harbinger of GM1.2,–5 In rare disorders where expensive genetic testing and invasive procedures are often used to reach a diagnosis, recognition of unique clinical features on the physical examination can be a great asset.