Guemez-Gamboa, A., A. O. Çağlayan, V. Stanley, A. Gregor, M. S. Zaki, S. N. Saleem, D. Musaev, J. McEvoy-Venneri, D. Belandres, N. Akizu, et al.,
"Loss of Protocadherin-12 Leads to Diencephalic-Mesencephalic Junction Dysplasia Syndrome.",
Annals of neurology, vol. 84, issue 5, pp. 638-647, 2018 Nov.
AbstractOBJECTIVE: To identify causes of the autosomal-recessive malformation, diencephalic-mesencephalic junction dysplasia (DMJD) syndrome.
METHODS: Eight families with DMJD were studied by whole-exome or targeted sequencing, with detailed clinical and radiological characterization. Patient-derived induced pluripotent stem cells were derived into neural precursor and endothelial cells to study gene expression.
RESULTS: All patients showed biallelic mutations in the nonclustered protocadherin-12 (PCDH12) gene. The characteristic clinical presentation included progressive microcephaly, craniofacial dysmorphism, psychomotor disability, epilepsy, and axial hypotonia with variable appendicular spasticity. Brain imaging showed brainstem malformations and with frequent thinned corpus callosum with punctate brain calcifications, reflecting expression of PCDH12 in neural and endothelial cells. These cells showed lack of PCDH12 expression and impaired neurite outgrowth.
INTERPRETATION: DMJD patients have biallelic mutations in PCDH12 and lack of protein expression. These patients present with characteristic microcephaly and abnormalities of white matter tracts. Such pathogenic variants predict a poor outcome as a result of brainstem malformation and evidence of white matter tract defects, and should be added to the phenotypic spectrum associated with PCDH12-related conditions. Ann Neurol 2018;84:646-655.
Escande-Beillard, N., A. Loh, S. N. Saleem, K. Kanata, Y. Hashimoto, U. Altunoglu, A. Metoska, J. Grandjean, F. M. Ng, O. Pomp, et al.,
"Loss of PYCR2 Causes Neurodegeneration by Increasing Cerebral Glycine Levels via SHMT2.",
Neuron, vol. 107, issue 1, pp. 82-94.e6, 2020.
AbstractPatients lacking PYCR2, a mitochondrial enzyme that synthesizes proline, display postnatal degenerative microcephaly with hypomyelination. Here we report the crystal structure of the PYCR2 apo-enzyme and show that a novel germline p.Gly249Val mutation lies at the dimer interface and lowers its enzymatic activity. We find that knocking out Pycr2 in mice phenocopies the human disorder and depletes PYCR1 levels in neural lineages. In situ quantification of neurotransmitters in the brains of PYCR2 mutant mice and patients revealed a signature of encephalopathy driven by excessive cerebral glycine. Mechanistically, we demonstrate that loss of PYCR2 upregulates SHMT2, which is responsible for glycine synthesis. This hyperglycemia could be partially reversed by SHMT2 knockdown, which rescued the axonal beading and neurite lengths of cultured Pycr2 knockout neurons. Our findings identify the glycine metabolic pathway as a possible intervention point to alleviate the neurological symptoms of PYCR2-mutant patients.
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