OMIM ID:
Mannosidosis, Alpha B
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
Many (probably most) patients have lens opacities and some have corneal opacities as well. Nystagmus and strabismus have been described. Pigmentary changes of a mottled nature can be present in the posterior pole and may be associated with retinal vessel attenuation and diminished ERG responses. Retinal thinning can be demonstrated. A mixture of hypo- and hyperautofluorescence is often visible. Mild optic atrophy has been seen. There is evidence for progressive visual loss, even late in life. Eyebrows appear thick.
Systemic Features
Mannosidosis is a highly variable multisystem disorder. Onset may be in infancy but in other patients symptoms appear later in the first decade. Progression of disease is more rapid in individuals with early onset (type 3) with rapid mental, motor deterioration and early death. The characteristic coarse facial features usually are evident later in milder cases (types 1 and 2) that have mild or moderate intellectual disabilities. Regardless, mannosidosis is relentlessly progressive with mental deterioration and motor disabilities. Ataxia is a common feature. Dental anomalies (diastema), large ears, macroglossia, joint stiffness,, hepatosplenomegaly, enlarged head circumference, hearing loss (sensorineural), increased susceptibility to infections, dysarthria, and spondylolysis may be present.
Genetics
Inheritance
Pedigree
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.