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.

We used exome sequencing of blood DNA in four unrelated patients to identify the genetic basis of metaphyseal chondromatosis with urinary excretion of D-2-hydroxy-glutaric acid (MC-HGA), a rare entity comprising severe chondrodysplasia, organic aciduria, and variable cerebral involvement. No evidence for recessive mutations was found; instead, two patients showed mutations in IDH1 predicting p.R132H and p.R132S as apparent somatic mosaicism. Sanger sequencing confirmed the presence of the mutation in blood DNA in one patient, and in blood and saliva (but not in fibroblast) DNA in the other patient. Mutations at codon 132 of IDH1 change the enzymatic specificity of the cytoplasmic isocitrate dehydrogenase enzyme. They result in increased D-2-hydroxy-glutarate production, a-ketoglutarate depletion, activation of HIF-1a (a key regulator of chondrocyte proliferation at the growth plate), and reduction of N-acetylaspartyl-glutamate level in glial cells. Thus, somatic mutations in IDH1 may explain all features of MC-HGA, including sporadic occurrence, metaphyseal disorganization, and chondromatosis, urinary excretion of D-2-hydroxy-glutaric acid, and reduced cerebral myelinization.

Congenital disorders of glycosylation type 1 (CDG-I) comprise a group of 27 genetic defects with heterogeneous multisystem phenotype, mostly presenting with nonspecific neurological symptoms. The biochemical hallmark of CDG-I is a partial absence of complete N-glycans on transferrin. However,

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.

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