Lysosomal storage disorders.

Lysosomes are intra-cellular organelles that are responsible for degrading and recycling macromolecules. Lysosomal diseases (LDs) are a group of rare inherited diseases caused by deleterious variants affecting genes that encode the lysosomal enzymes, their transporter or their cofactor. Among LDs that are associated with lung involvement and/or interstitial lung disease (ILD) acid sphingomyelinase deficiency [ASMD formerly called Niemann-Pick A, AB and B diseases]) is the most common. An history of lower respiratory tract infections and exertional dyspnoea are the most frequent respiratory manifestations. In ASMD, ILD is frequent and is usually associated with spleen and/or liver enlargement, low platelet count, and low level of high-density lipoprotein-cholesterol. A restrictive lung functional pattern and a reduction in DLCO value are usually observed. Analysis of bronchoalveolar lavage fluid and lung biopsy showing foamy cells can orientate the diagnosis, based on the demonstration of an enzymatic deficiency in sphingomyelinase in the blood, associated with biallelic pathogenic variants of the SMPD1 gene. An enzyme replacement therapy (ERT), based on intravenous recombinant enzyme infusions (olipudase alfa), is available from 2021 with very encouraging results both in pediatric and adult patients affected with type B or AB. Olipudase alfa administration decreased liver and spleen volume, increased DLCO value and improved radiological lung involvement. Available enzyme replacement therapy supports an early diagnosis to implement therapy before any irreversible organ damage.