<!-- add content re livestock -->
Alpha-mannosidosis is a lysosomal storage disorder, first described by Swedish physician Okerman in 1967. In humans it is known to be caused by an autosomal recessive genetic mutation in the gene MAN2B1, located on chromosome 19, affecting the production of the enzyme alpha-D-mannosidase, resulting in its deficiency. Consequently, if both parents are carriers, there will be a 25% chance with each pregnancy that the defective gene from both parents will be inherited, and the child will develop the disease. There is a two in three chance that unaffected siblings will be carriers (Figure 1).
Symptoms and signs
thumb|Facial features in alpha-mannosidosis. A. Twins aged 18 Months. Note enlarged head, short neck, rounded eyebrows, saddle nose, and prominent forehead. B. Same twins aged 8 years. Note slight muscular atrophy of the hands. C. Boy, aged 27. Note: Hearing aid.|left
Alpha-mannosidosis is a lifelong multi-systemic progressive disease, with neuromuscular and skeletal deterioration over decades. This delays diagnosis, particularly as milder forms of the disease involve only mild to moderate intellectual disability, which progresses gradually during childhood or adolescence.
The first decade of life is characterised by the development of hearing impairment, psychomotor delay, recurrent infections, especially upper airway infections, pulmonary infections and acute/serous otitis media infections. Complete absence of functionality in this enzyme leads to death during early childhood due to deterioration of the central nervous system.
Generally, phenotypes of alpha-mannosidosis patients are not clearly distinguishable, which makes a prediction of the clinical course for an individual patient challenging.
Prognosis
The long-term forecast for the condition is poor.