Autosomal recessive mental retardation, deafness, ankylosis, and mild hypophosphatemia associated with a novel ANKH mutation in a consanguineous family
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SourceJournal of Clinical Endocrinology and Metabolism, 96, 1, (2011), pp. E189-98
Article / Letter to editor
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Paediatrics - OUD tm 2017
Laboratory of Genetic, Endocrine and Metabolic Diseases
Journal of Clinical Endocrinology and Metabolism
SubjectDCN 1: Perception and Action IGMD 4: Glycostation disorders; DCN 3: Neuroinformatics; IGMD 3: Genomic disorders and inherited multi-system disorders; IGMD 3: Genomic disorders and inherited multi-system disorders DCN 2: Functional Neurogenomics; IGMD 6: Hormonal regulation; NCMLS 5: Membrane transport and intracellular motility IGMD 9: Renal disorder; NCMLS 6: Genetics and epigenetic pathways of disease DCN 2: Functional Neurogenomics
CONTEXT: Mutations in ANKH cause the highly divergent conditions familial chondrocalcinosis and craniometaphyseal dysplasia. The gene product ANK is supposed to regulate tissue mineralization by transporting pyrophosphate to the extracellular space. OBJECTIVE: We evaluated several family members of a large consanguineous family with mental retardation, deafness, and ankylosis. We compared their skeletal, metabolic, and serological parameters to that of the autosomal recessive progressive ankylosis (ank) mouse mutant, caused by a loss-of-function mutation in the murine ortholog Ank. PARTICIPANTS: The studied patients had painful small joint soft-tissue calcifications, progressive spondylarthropathy, osteopenia, mild hypophosphatemia, mixed hearing loss, and mental retardation. RESULTS: After mapping the disease gene to 5p15, we identified the novel homozygous ANK missense mutation L244S in all patients. Although L244 is a highly conserved amino acid, the mutated ANK protein was detected at normal levels at the plasma membrane in primary patient fibroblasts. The phenotype was highly congruent with the autosomal recessive progressive ankylosis (ank) mouse mutant. This indicates a loss-of-function effect of the L244S mutation despite normal ANK protein expression. Interestingly, our analyses revealed that the primary step of joint degeneration is fibrosis and mineralization of articular soft tissues. Moreover, heterozygous carriers of the L244S mutation showed mild osteoarthritis without metabolic alterations, pathological calcifications, or central nervous system involvement. CONCLUSION: Beyond the description of the first human progressive ankylosis phenotype, our results indicate that ANK influences articular soft tissues commonly involved in degenerative joint disorders. Furthermore, this human disorder provides the first direct evidence for a role of ANK in the central nervous system.
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