Hepatic storage of glycogen in Niemann-Pick disease type B

Lysosomal storage diseases

Lysosomes are cytoplasmic organelles that contain a variety of different hydrolases. A genetic deficiency in the enzymatic activity of one of these hydrolases will lead to the accumulation of the material meant for lysosomal degradation. Examples include glycogen in the case of Pompe disease, glycosaminoglycans in the case of the mucopolysaccharidoses, glycoproteins in the cases of the oligosaccharidoses, and sphingolipids in the cases of Niemann-Pick disease types A and B, Gaucher disease, Tay-Sachs disease, Krabbe disease, and metachromatic leukodystrophy. Sometimes, the lysosomal storage can be caused not by the enzymatic deficiency of one of the hydrolases, but by the deficiency of an activator protein, as occurs in the AB variant of GM2 gangliosidosis. Still other times, the accumulated lysosomal material results from failed egress of a small molecule as a consequence of a deficient transporter, as in cystinosis or Salla disease. In the last couple of decades, enzyme replacement therapy has become available for a number of lysosomal storage diseases. Examples include imiglucerase, taliglucerase and velaglucerase for Gaucher disease, laronidase for Hurler disease, idursulfase for Hunter disease, elosulfase for Morquio disease, galsulfase for Maroteaux-Lamy disease, alglucosidase alfa for Pompe disease, and agalsidase alfa and beta for Fabry disease. In addition, substrate reduction therapy has been approved for certain disorders, such as eliglustat for Gaucher disease. The advent of treatment options for some of these disorders has led to newborn screening pilot studies, and ultimately to the addition of Pompe disease and Hurler disease to the Recommended Uniform Screening Panel (RUSP) in 2015 and 2016, respectively.

Early pulmonary involvement in Niemann-Pick type B disease: lung lavage is not useful

Niemann-Pick disease (NPD) is a rare, autosomal-recessively inherited lipid storage disease which is characterized by intracellular deposition of sphingomyelin in various body tissues. The disease is heterogeneous and classified into six groups. Pulmonary parenchymal involvement may be a feature of several subtypes of NPD, including type B. Progressive pulmonary involvement in NPD type B is a major cause of morbidity and mortality. It is usually diagnosed at older ages. Only a few cases with early pulmonary involvement have been reported. In this report, a patient with NPD type B, hospitalized with the diagnosis of pneumonia at age 3 months, is presented. Following treatment for pneumonia, she continued to have persistent respiratory symptoms and became oxygen-dependent. High-resolution computed tomography of the chest revealed diffuse interstitial changes. During follow-up, the patient developed hepatosplenomegaly. Lung, liver, and bone marrow biopsies showed characteristic findings for NPD. Biochemical studies also confirmed the diagnosis, and the sphingomyelinase enzyme level of the patient was low. Unilateral lung lavage was performed in order to decrease lipid storage as a treatment modality. However, there was no clinical or radiological improvement. The patient died at age 15 months due to progressive respiratory failure. Pulmonary involvement is a rare entity in early childhood in patients with NPD type B, but should be considered in the differential diagnosis of persistent interstitial lung disease. It may cause progressive respiratory failure, but the treatment options remain limited.