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Intellectual disability v7.22 DPP6 Sarah Leigh Classified gene: DPP6 as Red List (low evidence)
Intellectual disability v7.22 DPP6 Sarah Leigh Gene: dpp6 has been classified as Red List (Low Evidence).
Intellectual disability v7.21 DPP6 Sarah Leigh Classified gene: DPP6 as Red List (low evidence)
Intellectual disability v7.21 DPP6 Sarah Leigh Gene: dpp6 has been classified as Red List (Low Evidence).
Intellectual disability v7.20 DPP6 Sarah Leigh changed review comment from: DPP6 variants have been associated with Intellectual developmental disorder, autosomal dominant 33 in OMIM (#: 616311), but not with a phenotype in Gen2Phen. To date two monoallelic variants have been associated with OMIM: 616311 in two unrelated families, where the affected individuals all had microcephaly and intellectual disability (PMID:23832105). Various Dpp6 knock-down mouse models, showed that these mice had significantly lower body and brain weights in comparison to wildtype and displayed behaviours characteristic of reduced learning abilities and impaired memory (PMID: 21943606; 23832105; 29651237).
The ClinGen Gene-Disease Validity score for this gene is "Disputed" (https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_3d41cebe-5490-419d-882d-4f3c6856be07-2021-05-05T160000.000Z), therefore, this gene will remain amber.; to: DPP6 variants have been associated with Intellectual developmental disorder, autosomal dominant 33 in OMIM (#: 616311), but not with a phenotype in Gen2Phen. To date two monoallelic variants have been associated with OMIM: 616311 in two unrelated families, where the affected individuals all had microcephaly and intellectual disability (PMID:23832105). Various Dpp6 knock-down mouse models, showed that these mice had significantly lower body and brain weights in comparison to wildtype and displayed behaviours characteristic of reduced learning abilities and impaired memory (PMID: 21943606; 23832105; 29651237).
The ClinGen Gene-Disease Validity score for this gene is "Disputed" (https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_3d41cebe-5490-419d-882d-4f3c6856be07-2021-05-05T160000.000Z), therefore, this gene will remain red.
Intellectual disability v7.20 DPP6 Sarah Leigh edited their review of gene: DPP6: Changed rating: AMBER
Intellectual disability v7.20 DPP6 Sarah Leigh changed review comment from: DPP6 variants have been associated with Intellectual developmental disorder, autosomal dominant 33 in OMIM (#: 616311), but not with a phenotype in Gen2Phen. To date two monoallelic variants have been associated with OMIM: 616311 in two unrelated families, where the affected individuals all had microcephaly and intellectual disability (PMID:23832105). Various Dpp6 knock-down mouse models, showed that these mice had significantly lower body and brain weights in comparison to wildtype and displayed behaviours characteristic of reduced learning abilities and impaired memory (PMID: 21943606; 23832105; 29651237).; to: DPP6 variants have been associated with Intellectual developmental disorder, autosomal dominant 33 in OMIM (#: 616311), but not with a phenotype in Gen2Phen. To date two monoallelic variants have been associated with OMIM: 616311 in two unrelated families, where the affected individuals all had microcephaly and intellectual disability (PMID:23832105). Various Dpp6 knock-down mouse models, showed that these mice had significantly lower body and brain weights in comparison to wildtype and displayed behaviours characteristic of reduced learning abilities and impaired memory (PMID: 21943606; 23832105; 29651237).
The ClinGen Gene-Disease Validity score for this gene is "Disputed" (https://search.clinicalgenome.org/kb/gene-validity/CGGV:assertion_3d41cebe-5490-419d-882d-4f3c6856be07-2021-05-05T160000.000Z), therefore, this gene will remain amber.
Intellectual disability v7.20 DPP6 Sarah Leigh Tag Q3_24_promote_green was removed from gene: DPP6.
Tag Q3_24_expert_review was removed from gene: DPP6.
Intellectual disability v7.20 DPP6 Sarah Leigh Deleted their comment
Intellectual disability v7.20 DPP6 Sarah Leigh Tag Q3_24_promote_green tag was added to gene: DPP6.
Tag Q3_24_expert_review tag was added to gene: DPP6.
Intellectual disability v7.20 DPP6 Sarah Leigh Classified gene: DPP6 as Amber List (moderate evidence)
Intellectual disability v7.20 DPP6 Sarah Leigh Added comment: Comment on list classification: Although only two DPP6 variants have so far been associated with OMIM:616311 (PMID:23832105), I feel that the mouse model evidence from three studies provides evidence to support the association between DPP6 variants and microcephaly and intellectual disability (PMID: 21943606; 23832105; 29651237).
Intellectual disability v7.20 DPP6 Sarah Leigh Gene: dpp6 has been classified as Amber List (Moderate Evidence).
Intellectual disability v7.19 DPP6 Sarah Leigh Publications for gene: DPP6 were set to 23832105
Intellectual disability v7.18 DPP6 Sarah Leigh edited their review of gene: DPP6: Added comment: DPP6 variants have been associated with Intellectual developmental disorder, autosomal dominant 33 in OMIM (#: 616311), but not with a phenotype in Gen2Phen. To date two monoallelic variants have been associated with OMIM: 616311 in two unrelated families, where the affected individuals all had microcephaly and intellectual disability (PMID:23832105). Various Dpp6 knock-down mouse models, showed that these mice had significantly lower body and brain weights in comparison to wildtype and displayed behaviours characteristic of reduced learning abilities and impaired memory (PMID: 21943606; 23832105; 29651237).; Changed rating: GREEN
Intellectual disability v6.11 DPP6 Achchuthan Shanmugasundram Tag Q4_23_demote_red was removed from gene: DPP6.
Tag Q4_23_NHS_review was removed from gene: DPP6.
Tag Q4_23_expert_review was removed from gene: DPP6.
Intellectual disability v6.11 DPP6 Sarah Leigh reviewed gene: DPP6: Rating: RED; Mode of pathogenicity: ; Publications: ; Phenotypes: ; Mode of inheritance:
Intellectual disability v6.10 DPP6 Achchuthan Shanmugasundram Source Expert Review Red was added to DPP6.
Source NHS GMS was added to DPP6.
Rating Changed from Green List (high evidence) to Red List (low evidence)
Intellectual disability v6.9 DPP6 Arina Puzriakova Phenotypes for gene: DPP6 were changed from autosomal dominant microcephaly and mental retardation; Mental retardation, autosomal dominant 33, 616311 to Intellectual developmental disorder, autosomal dominant 33, OMIM:616311
Intellectual disability v5.335 DPP6 Ivone Leong commented on gene: DPP6
Intellectual disability v5.335 DPP6 Ivone Leong Tag Q4_23_demote_red tag was added to gene: DPP6.
Tag Q4_23_NHS_review tag was added to gene: DPP6.
Tag Q4_23_expert_review tag was added to gene: DPP6.
Intellectual disability v5.332 DPP6 Gavin Ryan reviewed gene: DPP6: Rating: RED; Mode of pathogenicity: None; Publications: ; Phenotypes: ; Mode of inheritance: MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted
Intellectual disability v3.1556 FBXW7 Konstantinos Varvagiannis gene: FBXW7 was added
gene: FBXW7 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: FBXW7 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: FBXW7 were set to 33057194; 35395208; 30885698; 26482194; 19963109; 20332316
Phenotypes for gene: FBXW7 were set to Neurodevelopmental abnormality; Global developmental delay; Intellectual disability; Macrocephaly; Microcephaly; Abnormality of brain morphology; Abnormality of the corpus callosum; Abnormality of the cerebellum; Abnormality of the cardiovascular system; Seizures; Strabismus; Abnormality of the palate
Penetrance for gene: FBXW7 were set to unknown
Review for gene: FBXW7 was set to AMBER
Added comment: While Kaplanis et al (2020 - Ref1), identified FBXW7 among 285 genes significantly associated with developmental disorders, a recent study by Stephenson et al (2022 - Ref2) describes the neurodevelopmental phenotype of 35 individuals making this gene relevant to the current panel. There are previous reports of dn/inh germline variants in individuals (likely 7) with tumor predisposition although a neurodevelopmental phenotype was not reported in most cases.

There is currently no FBXW7-related phenotype in OMIM.

The gene is included in the DD panel of G2P [associated with: FBXW7-related developmental disorder (monoallelic), confidence: definitive, citing the study by Kaplanis et al]. SysID lists FBXW7 among the candidate ID genes (same Ref.). The gene has a green rating for ID in PanelApp Australia (VCGS participating in the recent publication).

Consider inclusion with amber/green rating. Also consider inclusion in other panels that may be relevant(macro/microcephaly, seizures, CHD, corpus callosum / cerebellar abnormalities, cleft palate, WT, etc).

[1]------------
Kaplanis et al (2020 - PMID: 33057194), by combining exome data from 31,058 parent offspring trios from the DDD study, Radboudumc and GeneDx, identified 285 genes significantly associated with developmental disorders, 28 of which (incl. FBXW7) not previously robustly associated with these disorders.

[2]------------
Stephenson et al (2022 - PMID: 35395208) provide clinical information on 35 individuals harboring germline monoallelic FBXW7 variants or chromosomal deletions spanning this gene.

The phenotype corresponded to a phenotypically variable NDD characterized by hypotonia (in about 2/3), neurodevelopmental abnormality (34/35 - as discussed later), seizures (8/35), abnormal brain morphology (13/17 - in 7/17 abnormal CC, in 5/17 abn. cerebellum, etc), head circumference (macrocephaly in 10/35, microcephaly in 2/35). Additional features included abnormal palate or uvula morphology (10/35 - cleft palate in 3 from 2 families while 1 individual from a 3rd family had bifid uvula) or abnormal heart morphology (11/35), ophthalmologic features (e.g. strabismus in 5/35) or hearing impairment (2/35). There was no recognizable gestalt (deeply set eyes with upper eyelid fullness in 9/35).

As for the DD/ID this ranged from borderline to severe, characterized as mild-moderate in 27/35, severe in 3/35. One individual did not present neurodevelopmental abnormality 1/35.

FBXW7 encodes F-box and WD40 domain protein 7 which is part of the SCF E3 ligase complex (SKP1/CUL1/F-box protein) exerting a role of recognition and binding of target proteins for degradation by the ubiquitin proteasome system. In this way FBWX7 participates in regulating a network of proteins involved in cell division, growth, differentiation (as summarized by Roversi et al - Ref2).

Most individuals were investigated by trio-WES/WGS (few with singleton WES or CMA only). 28 germline FBXW7 variants were identified incl. missense (N=21), pLoF (predicted or not to undergo NMD) and 2 deletions encompassing but not limited to FBXW7.

Additional SNVs/CNVs (e.g. an inh intragenic DPP6 dup in one individual (#9) with deletion, other de novo 4q CNVs (#10), an inh 22q spanning partially an ISCA TS region, a CACNA1A and KMT2D SNV, etc) were reported in few individuals.

Most variants arose dn (N=30) with two individuals displaying mosaicism (2/30) and three individuals having inherited the variant from their affected parent. CNVs had occurred dn.

3 missense SNVs were recurrent in unrelated individuals.

All variants identified affected all FBXW7 isoforms.

As the authors comment missense variants clustered at the C-terminal half of the protein with most (16/21) occurring within the WD40 domain. [The N-terminal part commented in the literature to affect localization].

The crystal structure of FBXW7 and SKP1 complex has been determined with CYCLIN E1/DISC1 as substrates, and in silico modeling revealed that all missense variants aligned with residues required for this interaction, or adjacent ones.

All were absent from gnomAD, while missense variants from gnomAD (N=78) were not predicted have significant effect on the binding affinity.

Variant studies revealed that most missense variants (6/7 tested - Arg689Gln being the exception) are unlikely to cause protein instability or degradation in vivo.

Co-expression of these missense variants with CYCLIN E1 / E2, known FBXW7 substrates revealed that variants were less efficient at degrading the substrate with variants in the WD40 domain having greater impact (in some cases E1 / E2 - specific).

Elav-Gal4 mediated neuronal knockdown of the Drosophila ortholog archipelago (ago) using 2 RNAi-s with different efficiency was shown to affect learning or compromise neuronal function (also related to the level of knockdown).

The authors summarize results from animal models for the role of this gene in development and the nervous system.

KO mice die in utero at E10.5 manifesting abn. of hematopoietic or vascular development and heart-chamber maturation(*). Some htz knock-in for human cancer variants, display perinatal lethality, abn lung, cleft palate (30%)(*),etc. Conditional gut specific deletion results in impaired differentiation of intestinal goblet cells (*)(constipation in 16/35 in cohort). KO limited to CNS and PNS results in defective sucking and morphological brain abnormalities. Haploinsufficiency in the nervous system was associated with impaired differentiation of neural stem cells (possibly through a Notch-mediated mechanism). KO in Schwann cells of the peripheral nervous system resulted in enhanced myelination.

Excessive oligodendrocyte cells and hypermyelination (as a result of elevated Notch & mTOR signaling) are observed in homozygous mutant zebrafish or after morpholino-mediated fbxw7 knockdown.

Overall, the authors propose haploinsufficiency or loss-of-function as the underlying mechanism.

Finally, as the authors comment, FBXW7 is a tumor suppressor among the most commonly mutated genes in human cancer (3.5%). Germline variants have been previously reported in individuals with cancer (Wilms tumor, rhabdoid, etc - most summarized below). However, none of the 35 individuals in this cohort (oldest 44 y.o.) had any history of cancer.

Reports of individuals with germline variants causing (monoallelic) disruption of FBXW7 - cases without DD/ID:

[3]------------
Mahamdallie et al (2019 - PMID: 30885698) investigated with WES a cohort of 890 individuals with Wilms tumor (799 non-familial disease, 91 from WT pedigrees). In this context they identified 4 individuals having developed WT (ages: 28-76m) with FBXW7 dn or inherited LoF variants (710G>A / p.Trp237* dn - 1972C>T / p.Arg658* - inh:NA, 1017_1021del5, 670C>T - paternal / p.Arg224* inh:NA - RefSeq not provided). One additional individual with a missense variant (1753A>T / p.Ser585Cys - dn) had developed rhabdoid tumor. While the authors mentioned additional features for other subjects in their cohort, among the 5 individuals with FBXW7 variants, only one had hypotonia (ID_0592) and another (ID_7520) had two febrile convulsions.

[4]------------
Roversi et al (2015 - PMID: 26482194) described the phenotype of a 34 y.o. female with syndromic presentation (macrocephaly, nephrotic syndrome due to FSGS, Hodgkin's lymphoma, Wilms tumor, ovarian cystadenoma, breast carcinoma) harboring a 157 kb deletion of 4q31.3.

Eventual DD/ID was not reported despite detailed clinical description.

The deletion spanned almost the entire FBXW7 gene and a pseudogene (hg19 - chr4:153205202-153362047). The authors provided evidence that the del affected the maternal allele as dn event (maternal mosaicism excluded). Expression of FBXW7 in patient-derived EBV lymphoblastoid cell line revealed decreased levels of expression compared to controls. At somatic level, the authors looked for eventual 2nd hit in tumor tissue (which was not the case) while they demonstrated decreased FBXW7 expression in a WT sample compared to normal renal tissue. Previously, variants in other genes candidate for the phenotype were ruled out (Sanger & MLPA for TP53, BRCA1/2, PALB2, WT1, 11p15 MS-MLPA, std karyotype).

[5]------------
Kuiper et al (2015 - PMID: 19963109), in a 58 y.o. patient with recurrence of RCC, identified a constitutional translocation [t(3;4)(q21;q31)]. Using long-range PCR they defined the breakpoints at 3q21.3 (128379059 - hg18) between the PLXNA1 and C3orf56 genes while the chr4 breakpoint was located within the second intron of FBXW7 (pos. 153500813 - hg18). There were no additional phenotypes reported.

[6]------------
Williams et al (2010 - PMID: 20332316) reported a patient with WT harboring germline variants in WT1 and FBXW7. While the phenotype was sufficiently explained by a germline stopgain WT1 variant with a frameshift WT1 variant (as 2nd hit) confined to the tumor, the authors identified a germline in-frame FBXW7 insertion in the same individual (c.45_46insCCT / p.Thr15_Gly16insPro - RefS : NA) [if correct corresponding to: https://gnomad.broadinstitute.org/variant/4-153332910-C-CAGG - 345/281696 alleles in gnomAD].
Sources: Literature
Intellectual disability DPP6 Rebecca Foulger classified DPP6 as green
Intellectual disability DPP6 Rebecca Foulger commented on DPP6
Intellectual disability DPP6 Rebecca Foulger commented on DPP6
Intellectual disability DPP6 Rebecca Foulger added DPP6 to panel
Intellectual disability DPP6 Rebecca Foulger reviewed DPP6