Intellectual disability - microarray and sequencing
Gene: IQSEC1 Amber List (moderate evidence)This gene will be kept as Amber until more evidence is available.Created: 19 Oct 2020, 2:33 p.m. | Last Modified: 19 Oct 2020, 2:33 p.m.
Panel Version: 3.460
Green List (high evidence)
Five individuals from two unrelated families plus functional data from two model organisms. We have rated this gene Green.Created: 8 Feb 2020, 7:14 a.m. | Last Modified: 8 Feb 2020, 7:14 a.m.
Panel Version: 3.0
Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal
Phenotypes
Intellectual developmental disorder with short stature and behavioral abnormalities, MIM# 618687
Publications
Variants in this GENE are reported as part of current diagnostic practice
I don't know
Comment on list classification: Expert review by Konstantinos Varvagiannis on IQSEC1 following a publication by Ansar et al. (2019 - PMID: 31607425) who reported on 5 individuals with biallelic IQSEC1 variants.
IQSEC1 is not in OMIM or Gene2Phenotype. There are <3 individuals/variants/families where ID is reported. Therefore classify IQSEC1 as Amber until more evidence is available.Created: 26 Nov 2019, 3:34 p.m. | Last Modified: 26 Nov 2019, 3:34 p.m.
Panel Version: 2.1119
Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal
Publications
I don't know
Ansar et al. (2019 - PMID: 31607425) reported on 5 individuals with biallelic IQSEC1 variants.
Common features included hypotonia, DD, speech impairment, severe ID, behavioral problems as well as short stature. Early-onset seizures were observed in 3 sibs (for whom there was also a paternal family history of seizures).
These subjects belonging to 2 consanguineous families from Pakistan and S. Arabia were found to harbor homozygous missense variants private to each family (Fam1: NM_001134382.2:c.1028C>T or p.Thr354Met following SNP genotyping of several members and exome of the proband | Fam2: c.962G>A or p.Arg321Gln following exome in 2 affected members). Sanger confirmation and study of parents (+/- sibs) were compatible.
The homozygous variant was the only candidate in the 1st family (also following exclusion of other causes of ID/short stature), and most likely/compatible with the patient's phenotype in the 2nd.
As the authors note, IQSEC1-3 encode guanine exchange factors (GEFs) for the ARF family of GTPases. IQSEC2 is a known XLID gene, while biallelic IQSEC3 mutations in ID have been recently reported (PMID: 31130284), all presenting phenotypic similarities (ID, short stature, speech defect).
Previous studies cited had shown that IQSEC1 & 2 are concentrated at the postsynaptic density of glutamatergic synapses in mammalian brain, playing a role in actin-dependent processes incl. AMPA receptor trafficing at synapses (all refs in article).
Drosophila model: The ortholog of IQSEC1, 2 and 3 is schizo and the phenotype associated with its loss is a growth cone guidance defect through dysregulation of the Slit-Robo pathway (all refs in article). The authors studied overexpression of either reference IQSEC1 cDNA or variant cDNAs in wt flies, the former only being toxic/lethal. Loss of schizo was also embryonically lethal but was partially rescued by expression of reference IQSEC1 cDNA. Expression of cDNA for the 2 variants did not rescue lethality. As a result LoF appears to be the underlying effect of both variants. The authors provided evidence that schizo is localized in glia and neurons at various stages of development and is important for proper axon guidance in both CNS and PNS. In Drosophila, schizo is also localized in photoreceptors and RNAi-mediated knockdown resulted in severely impaired sight (also observed in 1 patient).
Mouse model: Through generation of Iqsec1-floxed mice, it was demonstrated that targeted depletion of Iqsec1 in the cortex resulted in increased density/immature morphology of dendritic spines.
IQSEC1 is not associated with any phenotype in OMIM / G2P / SysID and not commonly included in gene panels for ID.
As a result, this gene could be considered for inclusion in the ID panel as probably as amber (2 families/variants).
Sources: LiteratureCreated: 11 Nov 2019, 3:17 p.m.
Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal
Phenotypes
Central hypotonia; Global developmental delay; Intellectual disability; Behavioral abnormality; Short stature
Publications
Tag watchlist tag was added to gene: IQSEC1.
Phenotypes for gene: IQSEC1 were changed from Central hypotonia; Global developmental delay; Intellectual disability; Behavioral abnormality; Short stature to Central hypotonia; Global developmental delay; Intellectual disability; Behavioral abnormality; Short stature; Intellectual developmental disorder with short stature and behavioral abnormalities, 618687
Gene: iqsec1 has been classified as Amber List (Moderate Evidence).
gene: IQSEC1 was added gene: IQSEC1 was added to Intellectual disability. Sources: Literature Mode of inheritance for gene: IQSEC1 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: IQSEC1 were set to 31607425 Phenotypes for gene: IQSEC1 were set to Central hypotonia; Global developmental delay; Intellectual disability; Behavioral abnormality; Short stature Penetrance for gene: IQSEC1 were set to Complete Review for gene: IQSEC1 was set to AMBER
If promoting or demoting a gene, please provide comments to justify a decision to move it.
Genes included in a Genomics England gene panel for a rare disease category (green list) should fit the criteria A-E outlined below.
These guidelines were developed as a combination of the ClinGen DEFINITIVE evidence for a causal role of the gene in the disease(a), and the Developmental Disorder Genotype-Phenotype (DDG2P) CONFIRMED DD Gene evidence level(b) (please see the original references provided below for full details). These help provide a guideline for expert reviewers when assessing whether a gene should be on the green or the red list of a panel.
A. There are plausible disease-causing mutations(i) within, affecting or encompassing an interpretable functional region(ii) of this gene identified in multiple (>3) unrelated cases/families with the phenotype(iii).
OR
B. There are plausible disease-causing mutations(i) within, affecting or encompassing cis-regulatory elements convincingly affecting the expression of a single gene identified in multiple (>3) unrelated cases/families with the phenotype(iii).
OR
C. As definitions A or B but in 2 or 3 unrelated cases/families with the phenotype, with the addition of convincing bioinformatic or functional evidence of causation e.g. known inborn error of metabolism with mutation in orthologous gene which is known to have the relevant deficient enzymatic activity in other species; existence of an animal model which recapitulates the human phenotype.
AND
D. Evidence indicates that disease-causing mutations follow a Mendelian pattern of causation appropriate for reporting in a diagnostic setting(iv).
AND
E. No convincing evidence exists or has emerged that contradicts the role of the gene in the specified phenotype.
(i)Plausible disease-causing mutations: Recurrent de novo mutations convincingly affecting gene function. Rare, fully-penetrant mutations - relevant genotype never, or very rarely, seen in controls. (ii) Interpretable functional region: ORF in protein coding genes miRNA stem or loop. (iii) Phenotype: the rare disease category, as described in the eligibility statement. (iv) Intermediate penetrance genes should not be included.
It’s assumed that loss-of-function variants in this gene can cause the disease/phenotype unless an exception to this rule is known. We would like to collect information regarding exceptions. An example exception is the PCSK9 gene, where loss-of-function variants are not relevant for a hypercholesterolemia phenotype as they are associated with increased LDL-cholesterol uptake via LDLR (PMID: 25911073).
If a curated set of known-pathogenic variants is available for this gene-phenotype, please contact us at [email protected]
We classify loss-of-function variants as those with the following Sequence Ontology (SO) terms:
Term descriptions can be found on the PanelApp homepage and Ensembl.
If you are submitting this evaluation on behalf of a clinical laboratory please indicate whether you report variants in this gene as part of your current diagnostic practice by checking the box
Standardised terms were used to represent the gene-disease mode of inheritance, and were mapped to commonly used terms from the different sources. Below each of the terms is described, along with the equivalent commonly-used terms.
A variant on one allele of this gene can cause the disease, and imprinting has not been implicated.
A variant on the paternally-inherited allele of this gene can cause the disease, if the alternate allele is imprinted (function muted).
A variant on the maternally-inherited allele of this gene can cause the disease, if the alternate allele is imprinted (function muted).
A variant on one allele of this gene can cause the disease. This is the default used for autosomal dominant mode of inheritance where no knowledge of the imprinting status of the gene required to cause the disease is known. Mapped to the following commonly used terms from different sources: autosomal dominant, dominant, AD, DOMINANT.
A variant on both alleles of this gene is required to cause the disease. Mapped to the following commonly used terms from different sources: autosomal recessive, recessive, AR, RECESSIVE.
The disease can be caused by a variant on one or both alleles of this gene. Mapped to the following commonly used terms from different sources: autosomal recessive or autosomal dominant, recessive or dominant, AR/AD, AD/AR, DOMINANT/RECESSIVE, RECESSIVE/DOMINANT.
A variant on one allele of this gene can cause the disease, however a variant on both alleles of this gene can result in a more severe form of the disease/phenotype.
A variant in this gene can cause the disease in males as they have one X-chromosome allele, whereas a variant on both X-chromosome alleles is required to cause the disease in females. Mapped to the following commonly used term from different sources: X-linked recessive.
A variant in this gene can cause the disease in males as they have one X-chromosome allele. A variant on one allele of this gene may also cause the disease in females, though the disease/phenotype may be less severe and may have a later-onset than is seen in males. X-linked inactivation and mosaicism in different tissues complicate whether a female presents with the disease, and can change over their lifetime. This term is the default setting used for X-linked genes, where it is not known definitately whether females require a variant on each allele of this gene in order to be affected. Mapped to the following commonly used terms from different sources: X-linked dominant, x-linked, X-LINKED, X-linked.
The gene is in the mitochondrial genome and variants within this can cause this disease, maternally inherited. Mapped to the following commonly used term from different sources: Mitochondrial.
Mapped to the following commonly used terms from different sources: Unknown, NA, information not provided.
For example, if the mode of inheritance is digenic, please indicate this in the comments and which other gene is involved.