Biochemical Studies in Sphingomyelin Storage Disorders

Abstract

Inherited sphingomyelin storage disorders, more often referred to as Niemann-Pick disease, constitute a heterogeneous group both from a clinical and a biochemical point of view. The division into four types, first proposed by Crocker in 1961 (5), which is still widely used, delineates an infantile neuropathic form, or type A, a non-neuropathic form or type B, a subacute or juvenile form, also called type C, and a so-called Nova Scotia variant or type D. From a clinical point of view, the classification appears quite satisfactory as regards type A and B. Biochemically, a severe storage of sphingomyelin in visceral organs and a profound deficiency of sphingomyelinase have constantly been found in patients with these two phenotypes, but storage in brain only occurs in type A. With regard to the other forms of the disease, there is however much confusion. Delineation between type C and D is quite unclear. Furthermore, on the basis of specific clinical signs, other subgroups have been proposed (14), and some patients reported in the literature have been considered to represent a new nosological entity (26). With regard to the biochemical findings in those patients, a varying degree of sphingomyelin storage and either partial deficiency or normal activity of sphingomyelinase have been reported, without systematic correlation to a given clinical form.