Alpha-Mannosidosis in a 3.5-Year-Old Girl: A Case Report

Alpha-mannosidosis is a rare lysosomal storage disease caused by a deficiency of the enzyme alpha-mannosidase. It manifests as a continuous spectrum of signs and symptoms characterized by dysmorphic features, skeletal abnormalities, delayed psychomotor and speech development, impaired hearing, and psychiatric involvement. When suspected, alpha-mannosidosis must be confirmed by biochemical and molecular testing, namely, assessment of blood levels of alpha-mannosidase in leukocytes or fibroblasts and Sanger or next-generation sequencing of the MAN2B1 gene. The disease must be diagnosed and treatment started as quickly as possible, since the long-term prognosis for untreated patients is very poor. Enzyme replacement therapy (ERT, human recombinant alpha-mannosidase) has replaced allogeneic stem cell transplant as the mainstay of therapy, thus improving disease-related outcomes with, for example, reduced serum oligosaccharide levels, greater functional capacity, and improved quality of life, all with a good safety profile. We report the seventh case of alpha-mannosidosis in Spain. The patient was a 3.5-year-old girl assessed in the clinical genetics department for developmental delay and marked dysmorphic features (trigonocephaly, exophthalmos, hypertelorism, and a flat nasal bridge). Radiography revealed shortening and thickening of the long bones, as well as metopic and coronal synostosis. Craniosynostosis was treated with surgery. Assessment of alpha-mannosidase revealed complete absence of enzymatic activity. Genetic analysis revealed the homozygous pathogenic variant of MAN2B1, c.2248C>T, which is associated with alpha-mannosidosis. ERT is the only currently available pharmacological option for treating children with mild-to-moderate alpha-mannosidosis. Without ERT, patients' quality of life would be impaired, and their prognosis would worsen significantly.