Missense and Nonsense Mutations in the Lysosomal α-Mannosidase Gene (MANB) in Severe and Mild Forms of α-Mannosidosis

Abstract

alpha-Mannosidosis is an autosomal recessive lysosomal-storage disorder caused by a deficiency of lysosomal alpha-mannosidase activity. This disease shows a wide range of clinical phenotypes, from a severe, infantile form (type I), which is fatal at <3-8 years of age, to a less severe, late-onset form (type II), which ultimately may involve hearing loss, coarse face, mental retardation, and hepatosplenomegaly. To elucidate the molecular mechanism underlying this disease in both types of patients, we have used PCR, followed by either SSCP analysis or direct sequencing, to analyze the 24 exons and intron/exon boundaries of the alpha-mannosidase gene (MANB) from five patients. Two amino acid substitutions-H72L and R750W, in exons 2 and 18, respectively-and two nonsense mutations-Q639X and R760X, in exons 15 and 19, respectively-were identified in four type II patients. One amino acid substitution, P356R, was identified in exon 8 from a type I patient. This patient and three of the type II patients were homozygous for their mutations (H72L, P356R, R750W, and R760X) and one type II patient was heterozygous for the Q639X and R750W mutations. Transfection experiments of COS 7 cells, using the alpha-mannosidase cDNA containing one of the missense mutations-H72L, P356R, or R750W-revealed that each of these mutations dramatically reduces the enzymatic activity of alpha-mannosidase. These data demonstrate that widely heterogeneous missense or nonsense mutations of the MANB gene are the molecular basis underlying alpha-mannosidosis.

Early onset alpha‐mannosidosis with slow progression in three Hispanic males

“…3,4 This type is characterized by hepato-splenomegaly, severe dysostosis multiplex, hypotonia, rapidly progressive cognitive deterioration, and death, often occurring between 3 and 12 years of age. [3][4][5] The milder form of AMS is termed type II or the juvenile-adult phenotype. 3,4 Type II AMS is characterized by normal early development, mental retardation during childhood, and survival well into adulthood.…”

“…3,4 Type II AMS is characterized by normal early development, mental retardation during childhood, and survival well into adulthood. 4,5 Although patients have typically been placed into one of these two types of AMS, the clinical findings in patients may actually represent more of a continuum. 3 We describe three new cases of AMS in two families from Honduras.…”

Chronic enzyme replacement therapy ameliorates neuropathology in alpha‐mannosidosis mice

“…To enable chronic ERT, we developed immune‐tolerant alpha‐mannosidosis mice by transgenic expression of an active site mutant of human LAMAN under the control of the β ‐actin promotor in the alpha‐mannosidase knockout background. The insertion of a clinical mutation (c.215: A>T) within the human LAMAN cDNA leads to an exchange of a histidine to leucine at position 72 (H72L) in the active site resulting in an inactive form of the enzyme, which still localizes to lysosomes4, 5 (Fig. S1B–D).…”

Characterization of the mutant β-subunit of β-hexosaminidase for dimer formation responsible for the adult form of Sandhoff disease with the motor neuron disease phenotype

“…The enzyme activities using the MUG, MUGS and MUM substrates are referred to as MUG activity, MUGS activity and MUM activity, respectively. The efficiency of the DNA transfection was verified by measuring the E. coli b-galactosidase activity using o-nitrophenyl-b-D-galactopyranoside as the substrate (17). The protein concentration was determined using the Advanced Protein Assay Reagent (Cytoskeleton Inc., Denver, CO, USA).…”