Intellectual disability - microarray and sequencing
Gene: DHDDS Green List (high evidence)The mode of inheritance of this gene has been updated to 'MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted' following NHS Genomic Medicine Service approval.Created: 30 Jan 2023, 5:50 p.m. | Last Modified: 30 Jan 2023, 5:50 p.m.
Panel Version: 4.53
Comment on mode of inheritance: MOI should be updated from 'Both mono- and biallelic' to 'Monoallelic' at the next GMS panel update. Monoallelic variants are associated with a neurodevelopmental disorder comprising DD/ID, epilepsy and a variable movement disorder phenotype - >3 unrelated individuals reported in literature. To date, only one individual with biallelic variants and ID has been reported (PMID: 27343064). This patient presented with glycosylation defects but no corroborating cases have been reported since.
As only one patient has been described with biallelic inheritance and this phenotype, MOI should be set to 'Monoallelic' until evidence of additional cases emerges - biallelic variants would still be picked up by the Genomics England pipeline under this MOI.Created: 28 Oct 2021, 1:34 p.m. | Last Modified: 28 Oct 2021, 1:34 p.m.
Panel Version: 3.1395
Green List (high evidence)
Comment on list classification: Added DHDDS to panel and rated Green: Probable DD-G2P gene for 'Epilepsy and intellectual disability' and sufficient unrelated (>3) cases of ID phenotype associated with heterozygous DHDDS variants from PMID:29100083. Plus compound het case of patient with glycosylation disorder and complex developmental phenotypes from PMID:27343064.Created: 11 Dec 2018, 2:46 p.m.
Comment on mode of inheritance: Sabry et al (PMID:27343064) report a patient with DHDDS deficiency. The patient died at 8 months during a status epilepticus. The patient was compound heterozygous for variants in the DHDDS gene. The patient is also homozygous for the c.911 T>C (p.F304S) ALG6 variant that occurs in about one third of the population and does not cause CDG (but is a disease modifier to exacerbate symptoms in patients with glycosylation pathway defects). During his short life, the boy made little psychomotor acquisitions, had no eye contact, poor sucking with frequent regurgitations and failure to thrive. I have selected both monoallelic and biallelic MOI to cover MIM:617836 (AD) and future cases where ID presents as a symptom of a recessive glycosylation disorder.Created: 11 Dec 2018, 12:20 p.m.
In 5 unrelated patients with developmental delay and seizures with or without movement abnormalities (DEDSM; 617836), Hamdan et al. (2017, PMID:29100083) identified 2 different de novo heterozygous missense mutations in the DHDDS gene (R37H and R211Q). The ID phenotype of patients covers severe/moderate-to-severe ID and global developmental delay.
Sources: LiteratureCreated: 11 Dec 2018, 12:06 p.m.
Mode of inheritance
BOTH monoallelic and biallelic, autosomal or pseudoautosomal
Phenotypes
Developmental delay and seizures with or without movement abnormalities, 617836
Publications
Tag Q4_21_MOI was removed from gene: DHDDS.
Source NHS GMS was added to DHDDS. Mode of inheritance for gene DHDDS was changed from BOTH monoallelic and biallelic, autosomal or pseudoautosomal to MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted
Publications for gene: DHDDS were set to 29100083; 27343064
Tag Q4_21_MOI tag was added to gene: DHDDS.
Mode of inheritance for gene: DHDDS was changed from BOTH monoallelic and biallelic, autosomal or pseudoautosomal to BOTH monoallelic and biallelic, autosomal or pseudoautosomal
Phenotypes for gene: DHDDS were changed from Developmental delay and seizures with or without movement abnormalities, 617836; ?Congenital disorder of glycosylation, type 1bb, 613861 to Developmental delay and seizures with or without movement abnormalities, OMIM:617836
Gene: dhdds has been classified as Green List (High Evidence).
Phenotypes for gene: DHDDS were changed from Developmental delay and seizures with or without movement abnormalities, 617836 to Developmental delay and seizures with or without movement abnormalities, 617836; ?Congenital disorder of glycosylation, type 1bb, 613861
Mode of inheritance for gene: DHDDS was changed from BOTH monoallelic and biallelic, autosomal or pseudoautosomal to BOTH monoallelic and biallelic, autosomal or pseudoautosomal
gene: DHDDS was added gene: DHDDS was added to Intellectual disability. Sources: Literature Mode of inheritance for gene: DHDDS was set to BOTH monoallelic and biallelic, autosomal or pseudoautosomal Publications for gene: DHDDS were set to 29100083; 27343064 Phenotypes for gene: DHDDS were set to Developmental delay and seizures with or without movement abnormalities, 617836 Review for gene: DHDDS was set to GREEN
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.