De novo triplication at 1p36.23p36.22 further refines the dosage sensitive region of overlap in Setleis syndrome (focal facial dermal dysplasia type III).

Setleis syndrome (SS), or focal facial dermal dysplasia type III (FFDD3, MIM #227260), is an autosomal recessive condition caused by biallelic loss-of-function variants in TWIST2. It is characterized by bitemporal atrophic skin lesions and distinctive facial features. Individuals with de novo or inherited duplication or triplication of the chromosomal region 1p36.22p36.21 have also been reported to have the SS phenotype with additional neurodevelopmental challenges (rarely seen in individuals with TWIST2 mutations) and variable expressivity and penetrance. Triplication of this region is also associated with more severe manifestations compared to a duplication. We report a 2-year-old female patient with features of SS associated with a de novo 3.603 Mb triplication at 1p36.23p36.22 identified on postnatal microarray analysis. Her triplication shares a 281.263 kb overlap with gains at 1p36.22, reported by previous groups, delineating the shortest region of overlap (SRO) to date. This SRO involves 10 RefSeq and 4 OMIM morbid map genes and highlights the candidate dosage-sensitive element(s) underlying the cardinal features of SS phenotype in individuals with gains at 1p36.

Biallelic loss-of-function variants in RABGAP1 cause a novel neurodevelopmental syndrome.

PURPOSE: RABGAP1 is a GTPase-activating protein implicated in a variety of cellular and molecular processes, including mitosis, cell migration, vesicular trafficking, and mTOR signaling. There are no known Mendelian diseases caused by variants in RABGAP1. METHODS: Through GeneMatcher, we identified 5 patients from 3 unrelated families with homozygous variants in the RABGAP1 gene found on exome sequencing. We established lymphoblastoid cells lines derived from an affected individual and her parents and performed RNA sequencing and functional studies. Rabgap1 knockout mice were generated and phenotyped. RESULTS: We report 5 patients presenting with a common constellation of features, including global developmental delay/intellectual disability, microcephaly, bilateral sensorineural hearing loss, and seizures, as well as overlapping dysmorphic features. Neuroimaging revealed common features, including delayed myelination, white matter volume loss, ventriculomegaly, and thinning of the corpus callosum. Functional analysis of patient cells revealed downregulated mTOR signaling and abnormal localization of early endosomes and lysosomes. Rabgap1 knockout mice exhibited several features in common with the patient cohort, including microcephaly, thinning of the corpus callosum, and ventriculomegaly. CONCLUSION: Collectively, our results provide evidence of a novel neurodevelopmental syndrome caused by biallelic loss-of-function variants in RABGAP1.

Diagnostic outcomes for molecular genetic testing in children with suspected Ehlers-Danlos syndrome.

Ehlers-Danlos syndrome (EDS) is a heterogeneous group of connective tissue disorders characterized by hyperextensible skin, hypermobile joints, easy bruisability, and fragility of the connective tissues. The diagnosis is based on clinical assessment and phenotype-guided genetic testing. Most EDS subtypes can be confirmed by genetic testing except for hypermobile EDS. This study explored the utility of applying the 2017 EDS classification criteria and molecular genetic testing in establishing an EDS diagnosis in children. In this retrospective study, we reviewed 72 patients referred to a tertiary care center for evaluation of EDS who underwent one or more forms of genetic testing. Eighteen patients (18/72, 25%) met the clinical criteria for one of the EDS subtypes and of these, 15 (15/18, 83%) were confirmed molecularly. Fifty-four patients (54/72, 75%) had features that overlapped EDS and other syndromes associated with joint hypermobility but did not fully meet clinical criteria. Twelve of them (12/54, 22%) were later shown to have a positive molecular genetic diagnosis of EDS. Different molecular genetic tests were performed on the cohort of 72 patients (EDS panel, n = 44; microarray, n = 25; whole exome sequencing [WES], n = 9; single gene sequencing, n = 3; familial variant testing, n = 10; other genetic panels n = 3). EDS panel was completed in 44 patients (61%), and a molecular diagnosis was confirmed in nine of the patients who satisfied criteria for one of the EDS subtypes (9/12, 75%) and in nine of the patients who did not fully meet criteria (9/32, 28%). We observed a correlation between generalized joint hypermobility, poor healing, easy bruising, atrophic scars, skin hyperextensibility, and developmental dysplasia of the hip with a positive molecular result. This study provides guidance for the use of molecular genetic testing in combination with the 2017 clinical diagnostic criteria in children presenting with EDS characteristics.