Long-term outcome of patients with alpha-mannosidosis – A single center study

INTRODUCTION: Alpha-mannosidosis (AM) is a rare autosomal recessive lysosomal storage disease which the natural history has not been exhaustively described yet. The aim of this study was to present the long-term follow-up of 12 Polish patients with AM, evaluate the clinical, biochemical, and molecular findings and progression of the disease. MATERIAL AND METHODS: The article presents a long-term (over 30 years) observational, retrospective, single-center study of patients with AM. RESULTS: The hearing loss, as one of the first symptoms, was detected in childhood (mean age of 2 years and 6 months) in 10 patients. The other symptoms include: recurrent infections (all patients), inguinal hernias (6 patients), craniosynostosis (1 patient). The mean age at AM diagnosis was 6 years while median was 4 years (age range: 1 year and 8 months – 12 years). The most commonly identified variant in the MAN2B1 gene was c.2245C > T, p.(Arg749Trp). The mean time of follow-up in our study was approximately 14 years (range: 1 year – 26 years). Following birth, children with AM grow slowly, finally reaching the 3rd percentile (or values below the 3rd percentile). Hearing loss was not progressive while a gradual exacerbation of intellectual disability with no developmental regression was observed in all patients. Ataxia was diagnosed in 6 patients in the second decade of life (age range 15–20 years). CONCLUSIONS: Our study revealed the sensorineural hearing loss as one of the first noted symptom in AM which was congenital and non-progressive during the natural course of disease. A detailed anthropometric phenotype of AM patients was provided with observation of the growth decline during the long-term follow-up. Our study confirmed the existence of two distinguished clinical phenotypes of AM (mild and moderate), and also the lack of clear genotype-phenotype correlation.