RESUMEN
Genomics methodologies have significantly improved elucidation of Mendelian disorders. The combination with high-throughput functional-omics technologies potentiates the identification and confirmation of causative genetic variants, especially in singleton families of recessive inheritance. In a cohort of 99 individuals with abnormal Golgi glycosylation, 47 of which being unsolved, glycomics profiling was performed of total plasma glycoproteins. Combination with whole-exome sequencing in 31 cases revealed a known genetic defect in 15 individuals. To identify additional genetic factors, hierarchical clustering of the plasma glycomics data was done, which indicated a subgroup of four patients that shared a unique glycomics signature of hybrid type N-glycans. In two siblings, compound heterozygous mutations were found in SLC10A7, a gene of unknown function in human. These included a missense mutation that disrupted transmembrane domain 4 and a mutation in a splice acceptor site resulting in skipping of exon 9. The two other individuals showed a complete loss of SLC10A7 mRNA. The patients' phenotype consisted of amelogenesis imperfecta, skeletal dysplasia, and decreased bone mineral density compatible with osteoporosis. The patients' phenotype was mirrored in SLC10A7 deficient zebrafish. Furthermore, alizarin red staining of calcium deposits in zebrafish morphants showed a strong reduction in bone mineralization. Cell biology studies in fibroblasts of affected individuals showed intracellular mislocalization of glycoproteins and a defect in post-Golgi transport of glycoproteins to the cell membrane. In contrast to yeast, human SLC10A7 localized to the Golgi. Our combined data indicate an important role for SLC10A7 in bone mineralization and transport of glycoproteins to the extracellular matrix.
Asunto(s)
Enfermedades del Desarrollo Óseo/etiología , Calcificación Fisiológica , Trastornos Congénitos de Glicosilación/complicaciones , Genómica , Glicómica , Mutación , Transportadores de Anión Orgánico Sodio-Dependiente/genética , Péptido-N4-(N-acetil-beta-glucosaminil) Asparagina Amidasa/deficiencia , Simportadores/genética , Adulto , Animales , Enfermedades del Desarrollo Óseo/metabolismo , Enfermedades del Desarrollo Óseo/patología , Células Cultivadas , Estudios de Cohortes , Exoma , Femenino , Fibroblastos/metabolismo , Fibroblastos/patología , Glicosilación , Aparato de Golgi/metabolismo , Aparato de Golgi/patología , Humanos , Lactante , Masculino , Transportadores de Anión Orgánico Sodio-Dependiente/metabolismo , Linaje , Fenotipo , Transporte de Proteínas , Simportadores/metabolismo , Adulto Joven , Pez Cebra/genética , Pez Cebra/crecimiento & desarrollo , Pez Cebra/metabolismoRESUMEN
PURPOSE: Spinal cord involvement in Kearns-Sayre (KSS) syndrome could be more frequent than commonly thought. Our aims were to evaluate the involvement of the spinal cord in patients with KSS by means of MRI and to investigate possible correlations of spinal and brain disease with patient disability. METHODS: Eleven patients with KSS disease and spinal cord MRI were retrospectively recruited. The severity of spinal disease was defined as follows: grade 0 (none), grade 1 (focal), and grade 2 (extensive). We calculated a radiologic score of brain involvement based on typical features. We performed a chi-square test to correlate spinal cord and brain MRI involvement to patient disability. For significant variables, a contingency coefficient, phi factor, and Cramer's V were also computed. RESULTS: Spinal cord lesions were detected in 6/11 patients, showing four patterns: involvement of gray matter, gray matter and posterior columns, posterior columns, and anterior columns. The severity of spinal disease was grade 1 in two and grade 2 in four patients. All patients showed brain involvement (9-point average for patients with spinal involvement and 10 for the others). A significant correlation was found between disability score and spinal cord involvement (χ2 = 7.64; p = 0.022) or brain score (χ2 = 26.85; p = 0.043). Significance for brain score-disability correlation increased with the spinal cord as a cofactor (χ2 = 24.51; p = 0.017, phi factor = 1.201, Cramer's V = 0.849, contingency effect = 0.767; p = 0.017). CONCLUSION: Spinal cord lesions are common in KSS. Patients with spinal disease show higher disability than patients without spinal cord lesions, supporting the inclusion of dedicated acquisitions to routine MRI of the brain in patients with KSS.