Lysosomal Diseases

Key Features

• Lysosomal storage disorders may present clinically with multisystem involvement including hepatosplenomegaly, cardiac disease, and skeletal features, with or without neurologic involvement.

• Brain imaging, skeletal survey, and urinary mucopolysaccharide or oligosaccharide screen may be helpful initial screening studies; most diagnoses are made by enzyme assay.

• Most are inherited as autosomal recessive traits, and all can be diagnosed in utero

Clinical Findings

• Deficiency of a lysosomal enzyme causes its substrate to accumulate in the lysosomes, resulting in a characteristic clinical picture

• These storage disorders are classified as mucopolysaccharidoses, lipidoses, or mucolipidoses, depending on the nature of the stored material

• Two additional disorders, cystinosis and Salla disease, are caused by defects in lysosomal proteins that normally transport material from the lysosome to the cytoplasm

• See Table 36–3

Diagnosis

• The diagnosis of mucopolysaccharidosis is suggested by certain clinical and radiologic findings (dysostosis multiplex, which includes enlarged sella turcica, scaphocephaly, broad ribs, hook-shaped vertebrae [L1 and L2 most affected], and prominent pointing of the metacarpals and broad phalanges)

• Urine screening tests can detect increased mucopolysaccharides and further identify which specific mucopolysaccharides are present

• Diagnosis must be confirmed by enzyme assays of leukocytes or cultured fibroblasts

• Molecular analysis is also available for most conditions

Treatment

• Most conditions cannot be treated effectively

• Hematopoietic stem cell transplantation can greatly improve the course of some lysosomal diseases and is first-line treatment in some, such as infantile Hurler syndrome

• Several disorders are treated with infusions of recombinant modified enzyme