Search

Purpose: Missense variants clustering in the BTB domain region of RHOBTB2 cause a developmental and epileptic encephalopathy with early-onset seizures and severe intellectual disability., Methods: By international collaboration, we assembled individuals with pathogenic RHOBTB2 variants and a variable spectrum of neurodevelopmental disorders. By western blotting, we investigated the consequences of missense variants in vitro., Results: In accordance with previous observations, de novo heterozygous missense variants in the BTB domain region led to a severe developmental and epileptic encephalopathy in 16 individuals. Now, we also identified de novo missense variants in the GTPase domain in 6 individuals with apparently more variable neurodevelopmental phenotypes with or without epilepsy. In contrast to variants in the BTB domain region, variants in the GTPase domain do not impair proteasomal degradation of RHOBTB2 in vitro, indicating different functional consequences. Furthermore, we observed biallelic splice-site and truncating variants in 9 families with variable neurodevelopmental phenotypes, indicating that complete loss of RHOBTB2 is pathogenic as well., Conclusion: By identifying genotype-phenotype correlations regarding location and consequences of de novo missense variants in RHOBTB2 and by identifying biallelic truncating variants, we further delineate and expand the molecular and clinical spectrum of RHOBTB2-related phenotypes, including both autosomal dominant and recessive neurodevelopmental disorders., Competing Interests: Conflict of Interest Jeffrey B. Ratliff serves on the editorial board for the journal Neurology and has received consulting fees from Supernus Pharmaceuticals. All other authors declare no conflicts of interest., (Copyright © 2023 American College of Medical Genetics and Genomics. Published by Elsevier Inc. All rights reserved.)

Cytogenetic analysis of a low-grade endometrial stromal sarcoma of the uterus in a 52-year-old woman revealed the karyotype 46,XX,t(7;17)(p14 approximately 21;q11.2 approximately 21),der(7)t(7;16)(p14-15;q22)t(7;9) (q22;q22), der(9)t(7;9)(q22;q22),del(16)(q22). The t(7;17) was identical to an aberration observed in two other cases of endometrial stromal sarcomas, thus confirming the idea that it constitutes a non-random aberration for this type of tumor.

Cytogenetically visible aberrations of chromosomal region 12q14-15 in a variety of frequent benign human tumors reflect rearrangements of the HMGI-C gene. The mechanisms by which the HMGI-C gene contributes to tumorigenesis are mostly unknown, although frequently aberrant transcripts containing exons 1 to 3 of HMGI-C and ectopic sequences from other genes due to breaks within the third intron of HMGI-C are detectable. This is the first report analyzing human tissue samples mainly of mesenchymal origin by a highly sensitive polymerase-chain-reaction-based approach detecting HMGI-C expression. We found HMGI-C expression in embryonic tissue but no expression in any of several adult tissues tested except for two myometrial tissues. These data suggest that HMGI-C is mainly expressed in human tissues during embryonal and fetal development. Thus, its particular role for tumor development may be due to the expression of at least exons 1 to 3 rather than to the formation of fusion transcripts.

The results of cytogenetic studies of uterine leiomyomas have revealed that approximately 50% of these tumours are characterized by clonal chromosomal alterations. These karyotypic deviations are dominated by rearrangements involving a particular part of chromosome 12, i.e. region 12q13-15. We recently showed that the multiple aberration region on chromosome 12q15 harbours recurrent breakpoints frequently found in a variety of benign solid tumours. Within this region a gene encoding for a member of the so called high mobility group family proteins (HMG) was mapped. Further investigation revealed that this gene i.e. HMGI-C is often truncated by the chromosomal aberrations and fused to ectopic DNA sequences leading to fusion genes. Therefore, the results suggest a causal relationship between mutations of the HMGI-C gene and the development of uterine leiomyomas. Apparently identical mutations have been found also in endometrial polyps. Furthermore, there is an obvious coincidence between the chromosomal assignment of other members of the HMG family and the breakpoints of other non-random chromosome abnormalities seen in uterine leiomyomas.

Aberrations involving the chromosomal region 12q24 are a nonrandom cytogenetic abnormality in frequent benign tumors mainly of mesenchymal origin, e.g., uterine leiomyomas, pleomorphic adenomas of the salivary gland, lipomas, or hamartomas of the lung. Mostly, these 12q24 abnormalities occur as a result of inversions also affecting chromosomal region 12q14-15. In addition to the frequent tumors mentioned above, these abnormalities have also been found in rare mesenchymal tumors, e.g., hemangiopericytomas. Although recently the molecular basis of the aberrations of chromosomal region 12q14-15, i.e., a rearrangement of the HMGI-C gene has been identified, the molecular roots of the 12q24 changes still remain to be elucidated. Herein we report on 3' rapid amplification of cDNA ends PCR results on cDNA from a primary uterine leiomyoma. As an ectopic sequence fused to exon 3 of the HMGI-C gene, we have identified a cDNA sequence that revealed 100% homology to exon 13 of the human mitochondrial aldehyde dehydrogenase gene (ALDH 2). Because ALDH 2 maps to 12q24.1, this fusion transcript is a good candidate underlying the chromosomal rearrangements involving 12q24.

Recent molecular and cytogenetic studies on uterine leiomyoma cell lines with aberrations in 12q14-->q15 have shown that the chromosome 12 breakpoints seem to cluster in a 260-kb region designated as ULCR 12 (uterine leiomyoma cluster region of chromosome 12 breakpoints). Here we report the results of fluorescent in situ hybridization (FISH) studies using a molecular probe composed of five different cosmids that cover a 700-kb region encompassing ULCR 12. The FISH studies were performed on primary tumor specimens of uterine leiomyomas. With the exception of one case, our results demonstrated that the cosmid pool bridges the breakpoint region 12q14-->q15 in primary tumors as well. In the remaining case signal was localized distal to the breakpoint, indicating a breakpoint outside the region covered by the cosmid pool or a deletion in the region surrounding the chromosome 12 breakpoint. Individual cosmid probes from the pool were then used to narrow the localization of the breakpoint region in both the primary leiomyomas and established cell lines. The results showed that the breakpoints involving 12q14-->q15 in the primary uterine leiomyomas and derived cell lines are clustered in a single 170-kb breakpoint region within ULCR 12. For three of the cell lines studied, the breakpoint map within a 40-kb segment covered by one cosmid.