ZNHIT3 is defective in PEHO syndrome, a severe encephalopathy with cerebellar granule neuron loss

Brain. 2017 May 1;140(5):1267-1279. doi: 10.1093/brain/awx040.

Anna-Kaisa Anttonen ¹ ² ³ ⁴, Anni Laari ¹ ² ³, Maria Kousi ⁵, Yawei J Yang ⁶ ⁷ ⁸, Tiina Jääskeläinen ⁹ ¹⁰, Mirja Somer ¹¹, Eija Siintola ¹ ², Eveliina Jakkula ⁷, Mikko Muona ¹ ² ³ ⁷, Saara Tegelberg ¹ ² ³, Tuula Lönnqvist ⁸, Helena Pihko ⁸, Leena Valanne ¹², Anders Paetau ¹³, Melody P Lun ¹⁴ ¹⁵, Johanna Hästbacka ¹ ¹⁶, Outi Kopra ¹ ² ³, Tarja Joensuu ¹ ² ³, Nicholas Katsanis ⁵, Maria K Lehtinen ¹⁴, Jorma J Palvimo ⁹, Anna-Elina Lehesjoki ¹ ² ³

Affiliations

1 The Folkhälsan Institute of Genetics, Haartmaninkatu 8, 00290 Helsinki, Finland.
2 Neuroscience Center, University of Helsinki, Viikinkaari 4, 00790 Helsinki, Finland.
3 Research Programs Unit, Molecular Neurology, University of Helsinki, Haartmaninkatu 8, 00290 Helsinki, Finland.
4 Medical and Clinical Genetics, University of Helsinki and Helsinki University Hospital, Haartmaninkatu 8, 00290 Helsinki, Finland.
5 Center for Human Disease Modeling, Duke University Medical Center, Carmichael Building, 300 North Duke Street, Suite 48-118, Durham, NC 27701, USA.
6 Division of Genetics, Howard Hughes Medical Institute.
7 Institute for Molecular Medicine Finland, University of Helsinki, Haartmaninkatu 8, 00290 Helsinki, Finland.
8 Department of Pediatric Neurology, Children's Hospital, University of Helsinki and Helsinki University Hospital, Lastenlinnantie 2, 00290 Helsinki, Finland.
9 Institute of Biomedicine, University of Eastern Finland, Yliopistonranta 1, 70210 Kuopio, Finland.
10 Institute of Dentistry, University of Eastern Finland, Yliopistonranta 1, 70210 Kuopio, Finland.
11 The Norio Centre, The Rinnekoti Foundation, Kornetintie 8, 00380 Helsinki, Finland.
12 Department of Radiology, HUS Medical Imaging Center, Haartmaninkatu 4, 00290 Helsinki, Finland.
13 Department of Pathology, Helsinki University Hospital, Haartmaninkatu 3, 00290 Helsinki, Finland.
14 Department of Pathology, Boston Children's Hospital, BCH 3108, 300 Longwood Ave., Boston, MA 02115, USA.
15 Department of Pathology and Laboratory Medicine, Boston University School of Medicine, 670 Albany Street, Boston, MA 02118, USA.
16 Department of Pediatrics, Children's Hospital, University of Helsinki and Helsinki University Hospital, Stenbäckinkatu 11, 00290 Helsinki, Finland.

PMID: 28335020 DOI: 10.1093/brain/awx040

Abstract

Progressive encephalopathy with oedema, hypsarrhythmia, and optic atrophy (PEHO) syndrome is an early childhood onset, severe autosomal recessive encephalopathy characterized by extreme cerebellar atrophy due to almost total granule neuron loss. By combining homozygosity mapping in Finnish families with Sanger Sequencing of positional candidate genes and with exome Sequencing a homozygous missense substitution of leucine for serine at codon 31 in ZNHIT3 was identified as the primary cause of PEHO syndrome. ZNHIT3 encodes a nuclear Zinc Finger Protein previously implicated in transcriptional regulation and in small nucleolar ribonucleoprotein particle assembly and thus possibly to pre-ribosomal RNA processing. The identified mutation affects a highly conserved amino acid residue in the zinc finger domain of ZNHIT3. Both knockdown and genome editing of znhit3 in zebrafish embryos recapitulate the patients' cerebellar defects, microcephaly and oedema. These phenotypes are rescued by wild-type, but not mutant human ZNHIT3 mRNA, suggesting that the patient missense substitution causes disease through a loss-of-function mechanism. Transfection of cell lines with ZNHIT3 expression vectors showed that the PEHO syndrome mutant protein is unstable. Immunohistochemical analysis of mouse cerebellar tissue demonstrated ZNHIT3 to be expressed in proliferating granule cell precursors, in proliferating and post-mitotic granule cells, and in Purkinje cells. Knockdown of Znhit3 in cultured mouse granule neurons and ex vivo cerebellar slices indicate that ZNHIT3 is indispensable for granule neuron survival and migration, consistent with the zebrafish findings and patient neuropathology. These results suggest that loss-of-function of a nuclear regulator protein underlies PEHO syndrome and imply that establishment of its spatiotemporal interaction targets will be the basis for developing therapeutic approaches and for improved understanding of cerebellar development.

Keywords

PEHO syndrome; ZNHIT3; cerebellum; progressive encephalopathy.

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