Intellectual disability - microarray and sequencing
Gene: ATN1
As reviewed on the Genetic epilepsy syndromes (Version 1.178). Advice from the clinical team was that as phenotype is relevant it can be rated as Green.
Konstantinos Varvagiannis reviewed Palmer et al. (2019 - PMID: 30827498) who describes 8 individuals all with de novo variants in a specific and highly evolutionary conserved histidine-rich 16 amino acid motif encoded by exon 7 of ATN1. The pedigree analysis showed that all individuals are unrelated with different ancestry, all except one had undergone trio sequencing.
All individuals have DD/ID. ATN1 is in OMIM but is associated with the STR, it is in Gene2Phenotype as probable based on this paper.
ATN1_CAG STR is Green in a large number of panels and there are a number of publications associated with the STR. This is the first publication where variants within the gene and not the STR have been associated with this phenotypeCreated: 22 Jul 2019, 3:35 p.m. | Last Modified: 22 Jul 2019, 3:37 p.m.
Panel Version: 2.963
Palmer et al. (2019 - PMID: 30827498) report on 8 individuals all harboring de novo missense or insertion variants within a 16-amino-acid HX repeat motif (aa 1150-1065 / 8 HX repeats, where H is histidine and X any amino acid) in exon 7 of ATN1. The specific motif is distal to the Gln-rich region involved in Dentatorubro-pallidoluysian atrophy (caused by polyglutamine expansion in exon 5, due to a probable toxic GoF effect - MIM #125370). None of the subjects reported presented features of the latter disorder.
Common features included hypotonia (8/8) , DD and/or ID (8/8). Other frequent features included visual or hearing impairment, seizures (5/8 - in most presenting as neonatal/infantile onset dev. encephalopathy), feeding difficulties/functional GI disorders. Some individuals presented with congenital anomalies eg. cardiac, cleft palate, renal anomalies, anteriorly placed anus. Some facial (eg. presence of tall forehead, bitemporal narrowing, deep set eyes, sparse lateral hair, bulbous nose, open mouth appearance ,etc) or features of the extremities (overlapping fingers/toes) were also common.
Converging evidence from the literature suggests that ATN1 is a nuclear transcriptional regulator important in the control of brain and other organ development (PMIDs cited: 17150957, 25519973, 10973986). The gene is widely expressed in various tissues incl. brain, heart, lung, kidney, skeletal muscle. Expression is higher in fetal tissues particularly in brain while the gene is broadly expressed in multiple regions of the adult human brain (PMID: 7485154).
All 8 variants were missense SNVs or insertions within the HX repeat motif (aa 1150-1065) and had occurred as de novo events: c.3160C>A or p.His1054Asn, c.3172C>T or p.His1058Tyr, c.3177_3178insAACCTG or p.Ser1059_His1060insAsnLeu, c.3177_3178insGACCTG or p.Ser1059_His1060insAspLeu, c.3178C>T or p.His1060Tyr, c.3184C>G or p.His1062Asp, c.3188T>G or p.Leu1063Arg, c.3185A>G or p.His1062Arg [NM_001007026.1].
NMR studies of 2 commercialy synthesized polypeptides containing residues 1046-1067 of ATN1 and the HX motif suggested disruption in the case of His1060Tyr of the spatial and dynamical synchronization of histidines which is favored by the regularly spaced occurrence of histidines in the wild-type sequence. Under specific conditions introduction of His1060Tyr allowed zinc binding, which was not the case for the wild-type peptide, thus conferring the peptide a novel property (the consequences of which are though unknown). Clustering of the variants and presence of LoF in healthy individuals (eg. in gnomAD db) suggests that haploinsufficiency is unlikely.
Similar (HX)n repeat motifs exist in other proteins, among others RERE or AUTS2 which are associated with neurodevelopmental disorders. The authors comment that disruption of the HX motif in RERE has been reported in affected individuals and that mutations occurring in this motif are more likely to be associated with congenital anomalies, compared to mutations in the rest of the protein.
As for animal models, Atn1 -/- mice are neurologically normal. Knockdown of the gene in rat neuronal progenitor cells led to anomalies in brain development, though these could be rescued by co-transfection with human ATN1 construct (PMIDs cited: 17150957, 25519973).
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In OMIM, heterozygous pathogenic CAG trinucleotide expansions in ATN1 are associated with DRPLA (MIM #125370). The gene is not associated with any phenotype in G2P.
ATN1 is included in gene panels for ID offered by some diagnostic laboratories (eg. GeneDx participating in the aforementioned study).
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As a result, ATN1 can be considered for upgrade to green (or amber) in the ID panel.Created: 8 Mar 2019, 6:36 p.m.
Mode of inheritance
MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted
Phenotypes
Generalized hypotonia; Global developmental delay; Intellectual disability; Seizures; Feeding difficulties; Abnormality of the cardiovascular system; Cleft palate; Abnormality of the kidney
Publications
Mode of pathogenicity
Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Variants in this GENE are reported as part of current diagnostic practice
Associated with phenotype in OMIM, not in G2P. CNV expansion demonstrating anticipation. Phenotype not relevant to this panel as variants associated with late onset adult dementiaCreated: 15 Dec 2017, 9:38 a.m.
Mode of inheritance
MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications
Mode of pathogenicity
Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype -please provide details in the comments
This is a pertinent gene from the NIHR BioResource - Rare Diseases Study (NIHRBR-RD) BRIDGE Study : SPEED (Specialist Pathology: Evaluating Exomes in Diagnostics) which covers epilepsies, movement and microcephaly disorders, this gene is on the SPEED_NEURO_20170705 gene list. Evidences used for SPEED NEURO gene list: in_movement_disorder_list;in_UKGTN_v12 . Main mutation mechanism : NACreated: 27 Jul 2017, 5:07 p.m.
Evidences key, gene present in following gene lists and main mutation mechanism : manju_list; UKGTN_v12; Nijmegen_ID_candidates; neuro_20160418_strict; NA. This is a pertinent gene from the BRIDGE Study : SPEED (Specialist Pathology: Evaluating Exomes in Diagnostics) which covers epilepsies, movement and microcephaly disorders, this gene comes from the SPEED_NEURO_v3.0_20170404 gene list. The following experts from the BRIDGE consortium NIHRBR-RD contributed to this panel: - Professor F. Lucy Raymond, Cambridge Institute for Medical Research, University of Cambridge - Manju Kurian, Paediatric neurologist, Great Ormond Street Hosptial - Keren Carss, NIHR BioResource - Rare Diseases, Cambridge University Hospitals NHS Foundation Trust - Alba Sanchis-Juan, NIHR BioResource - Rare Diseases, Cambridge University Hospitals NHS Foundation Trust - Marie Erwood NIHR BioResource - Rare Diseases, Cambridge University Hospitals NHS Foundation Trust - Louise Daugherty, NIHR BioResource - Rare Diseases, Cambridge University Hospitals NHS Foundation TrustCreated: 19 Jul 2017, 12:02 p.m.
Mode of inheritance
Unknown
Publications
Comment on list classification: This gene is from an expert list and needs further assessment by the Genomics England curation team to access inclusion and pertinence to this panel.Created: 20 Jul 2017, 9:57 a.m.
Publications for gene: ATN1 were set to 24972706; 30827498
Phenotypes for gene: ATN1 were changed from Generalized hypotonia; Global developmental delay; Intellectual disability; Seizures; Feeding difficulties; Abnormality of the cardiovascular system; Cleft palate; Abnormality of the kidney to Congenital hypotonia, epilepsy, developmental delay, and digital anomalies, OMIM:618494
Phenotypes for gene: ATN1 were changed from Generalized hypotonia; Global developmental delay; Intellectual disability; Seizures; Feeding difficulties; Abnormality of the cardiovascular system; Cleft palate; Abnormality of the kidney to Generalized hypotonia; Global developmental delay; Intellectual disability; Seizures; Feeding difficulties; Abnormality of the cardiovascular system; Cleft palate; Abnormality of the kidney
Phenotypes for gene: ATN1 were changed from Dentatorubro-pallidoluysian atrophy 125370 to Generalized hypotonia; Global developmental delay; Intellectual disability; Seizures; Feeding difficulties; Abnormality of the cardiovascular system; Cleft palate; Abnormality of the kidney
Publications for gene: ATN1 were set to 24972706; 30827498
Publications for gene: ATN1 were set to 24972706
Mode of pathogenicity for gene: ATN1 was changed from to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Gene: atn1 has been classified as Green List (High Evidence).
Gene: atn1 has been classified as Green List (High Evidence).
12.03.2018: Due to major updates completed (Phase 1, 2 and 3), this panel was promoted to Version 2 in order to reflect the major updates since November 2017 which have resulted in reviews for 836 genes added by Genomics England Curators and the Clinical Team, 130 new Green genes added to the interpretation pipeline (from 751 to 881 Green genes), and the gene total has increased from 1879 to 1927.
Expert Review Red was added to ATN1. Panel: Intellectual disability Model of inheritance for gene ATN1 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown Publications for gene ATN1 was set to ['24972706']
This gene has been classified as Amber List (Moderate Evidence).
ATN1 was created by BRIDGE
ATN1 was added to Intellectual disabilitypanel. Sources: BRIDGE study SPEED NEURO Tier1 Gene