Whalen S, Shaw M, Mignot C, Héron D, Bastaraud SC, Walti CC, Liebelt J, Elmslie F, Yap P, Hurst J, Forsythe E, Kirmse B, Ozmore J, Spinelli AM, Calabrese O, de Villemeur TB, Tabet AC, Levy J, Guet A, Kossorotoff M, Kamien B, Morton J, McCabe A, Brischoux-Boucher E, Raas-Rothschild A, Pini A, Carroll R, Hartley JN; Care4Rare Canada Consortium; Frosk P, Slavotinek A, Truxal K, Jennifer C, Dheedene A, Cui H, Kumar V, Thomson G, Riccardi F, Gecz J, Villard L. Further delineation of BCAP31-linked intellectual disability: description of 17 new families with LoF and missense variants. Eur J Hum Genet. 2021 Sep;29(9):1405-1417. doi: 10.1038/s41431-021-00821-0. Epub 2021 Feb 18. PMID: 33603160; PMCID: PMC8440520.
Abstract
The BCAP31 gene, located at Xq28, encodes BAP31, which plays a role in ER-to-Golgi anterograde transport. To date, BCAP31 pathogenic variants have been reported in 12 male cases from seven families (six loss of function (LoF) and one missense). Patients had severe intellectual disability (ID), dystonia, deafness, and central hypomyelination, delineating a so-called deafness, dystonia and cerebral hypomyelination syndrome (DDCH). Female carriers are mostly asymptomatic but may present with deafness. BCAP31 is flanked by the SLC6A8 and ABCD1 genes. Contiguous deletions of BCAP31 and ABCD1 and/or SLC6A8 have been described in 12 patients. Patients with deletions including BCAP31 and SLC6A8 have the same phenotype as BCAP31 patients. Patients with deletions of BCAP31 and ABCD1 have contiguous ABCD1 and DXS1375E/BCAP31 deletion syndrome (CADDS), and demonstrate a more severe neurological phenotype with cholestatic liver disease and early death. We report 17 novel families, 14 with intragenic BCAP31 variants (LoF and missense) and three with a deletion of BCAP31 and adjacent genes (comprising two CADDS patients, one male and one symptomatic female). Our study confirms the phenotype reported in males with intragenic LoF variants and shows that males with missense variants exhibit a milder phenotype. Most patients with a LoF pathogenic BCAP31 variant have permanent or transient liver enzyme elevation. We further demonstrate that carrier females (n = 10) may have a phenotype comprising LD, ID, and/or deafness. The male with CADDS had a severe neurological phenotype, but no cholestatic liver disease, and the symptomatic female had moderate ID and cholestatic liver disease.
Cacciagli P, Sutera-Sardo J, Borges-Correia A, Roux JC, Dorboz I, Desvignes JP, Badens C, Delepine M, Lathrop M, Cau P, Lévy N, Girard N, Sarda P, Boespflug-Tanguy O, Villard L. Mutations in BCAP31 cause a severe X-linked phenotype with deafness, dystonia, and central hypomyelination and disorganize the Golgi apparatus. Am J Hum Genet. 2013 Sep 5;93(3):579-86. doi: 10.1016/j.ajhg.2013.07.023. PMID: 24011989; PMCID: PMC3769969.
Abstract
BAP31 is one of the most abundant endoplasmic reticulum (ER) membrane proteins. It is a chaperone protein involved in several pathways, including ER-associated degradation, export of ER proteins to the Golgi apparatus, and programmed cell death. BAP31 is encoded by BCAP31, located in human Xq28 and highly expressed in neurons. We identified loss-of-function mutations in BCAP31 in seven individuals from three families. These persons suffered from motor and intellectual disabilities, dystonia, sensorineural deafness, and white-matter changes, which together define an X-linked syndrome. In the primary fibroblasts of affected individuals, we found that BCAP31 deficiency altered ER morphology and caused a disorganization of the Golgi apparatus in a significant proportion of cells. Contrary to what has been described with transient-RNA-interference experiments, we demonstrate that constitutive BCAP31 deficiency does not activate the unfolded protein response or cell-death effectors. Rather, our data demonstrate that the lack of BAP31 disturbs ER metabolism and impacts the Golgi apparatus, highlighting an important role for BAP31 in ER-to-Golgi crosstalk. These findings provide a molecular basis for a Mendelian syndrome and link intracellular protein trafficking to severe congenital brain dysfunction and deafness.
Louie RJ, Collins DL, Friez MJ, Skinner C, Schwartz CE, Stevenson RE. Schimke XLID syndrome results from a deletion in BCAP31. Am J Med Genet A. 2020 Sep;182(9):2168-2174. doi: 10.1002/ajmg.a.61755. Epub 2020 Jul 18. PMID: 32681719.
Abstract
A family with three affected males and a second family with a single affected male with intellectual disability, microcephaly, ophthalmoplegia, deafness, and Involuntary limb movements were reported by Schimke and Associates in 1984. The affected males with Schimke X-linked intellectual disability (XLID) syndrome (OMIM# 312840) had a similar facial appearance with deep-set eyes, downslanting palpebral fissures, hypotelorism, narrow nose and alae nasi, cupped ears and spacing of the teeth. Two mothers had mild hearing loss but no other manifestations of the disorder. The authors considered the disorder to be distinctive and likely X-linked. Whole genome sequencing in the single affected male available and the three carrier females from one of the families with Schimke XLID syndrome identified a 2 bp deletion in the BCAP31 gene. During the past decade, pathogenic alterations of the BCAP31 gene have been associated with deafness, dystonia, and central hypomyelination, an XLID condition given the eponym DDCH syndrome. A comparison of clinical findings in Schimke XLID syndrome and DDCH syndrome shows them to be the same clinical entity. The BCAP31 protein functions in endoplasmic reticulum-associated degradation to promote ubiquitination and destruction of misfolded proteins.
Rinaldi B, Van Hoof E, Corveleyn A, Van Cauter A, de Ravel T. BCAP31-related syndrome: The first de novo report. Eur J Med Genet. 2020 Feb;63(2):103732. doi: 10.1016/j.ejmg.2019.103732. Epub 2019 Jul 19. PMID: 31330203.
Abstract
Pathogenic variants in the BCAP31 gene have recently been associated with a severe congenital neurological phenotype, named DDCH after its key features: deafness, dystonia and central hypomyelination. BCAP31 is located at the Xq28 chromosomal region and only male individuals are currently known to be affected, the pathogenic variant being usually transmitted by healthy mothers. Here, we describe a three-year-old male child referred for severe developmental delay, failure to thrive, hearing loss and dyskinetic movements. After a conventional diagnostic workflow, including a normal array-CGH, a tentative diagnosis of dyskinetic cerebral palsy was retained. Clinical exome sequencing in the trio identified a small intragenic deletion in exon 8 of BCAP31, c.709_721del (p.Val237Trpfs*69), originated de novo and not previously reported. Based on the ACMG variant classification, this variant is predicted to be 'likely pathogenic'. Given the consistent phenotypical overlap with the subjects already ascertained with DDCH, we considered this variant to be clinically relevant for this child and causative of his condition.
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