河村 理恵

BACKGROUND: Intrachromosomal insertion is a rare form of structural chromosomal rearrangement that often cannot be accurately delineated by conventional G-banding, making it difficult to predict reproductive outcomes. In clinical practice, such insertions are often misinterpreted as inversions or remain undetected, leading to recurrent segmental imbalances in offspring. We aimed to characterize an unresolved structural rearrangement identified in a family and to clarify its reproductive implications through advanced cytogenetic and molecular analyses. METHODS: Cytogenetic and molecular studies were conducted in a family where the proband exhibited a 17.8 Mb duplication at 9q21.31-q22.33. Although G-banding suggested a parental structural abnormality, its configuration could not be precisely defined. Subsequent preimplantation genetic testing for structural rearrangements (PGT-SR) using shallow whole-genome sequencing was performed on embryos, and further structural characterization was achieved through fluorescence in situ hybridization (FISH) and nanopore long-read sequencing. RESULTS: PGT-SR identified recurrent segmental imbalances involving the same region as in the proband, including four duplications and one deletion among 13 embryos. FISH and long-read sequencing demonstrated that the paternal rearrangement represented an intrachromosomal inverted insertion, described as ins(9)(q34.13q22.33q21.31). The father was phenotypically normal but transmitted unbalanced gametes generated by recombination between the insertion and original sites, leading to recurrent chromosomal abnormalities. CONCLUSIONS: This case highlights the potential of intrachromosomal insertions, although balanced in carriers, to cause recurrent segmental duplications or deletions in offspring. Comprehensive analysis using FISH and long-read sequencing is essential for accurate diagnosis, appropriate genetic counseling, and informed reproductive decision-making.

It is occasionally necessary to distinguish balanced reciprocal translocations from normal diploidy since balanced carriers can have reproductive problems or manifest other disease phenotypes. It is challenging to do this however using next generation sequencing (NGS) or microarray-based preimplantation genetic testing (PGT). In this study, discarded embryos were harvested from balanced reciprocal translocation carriers intending PGT that were determined to be unsuitable for transfer due to unbalanced translocations or translocation-unrelated aneuploidy. Two trophoectoderm biopsy samples were obtained from each single embryo. Whole genome amplification (WGA) was performed either by looping-based amplification (LBA) or multiple displacement amplification (MDA). NGS-based copy number variation (CNV) analysis as well as translocation-specific PCR was performed for each. We used embryo samples from t(8;22)(q24.13;q11.2) and t(11;22)(q23;q11.2) carriers since they are recurrent constitutional translocations that have nearly identical breakpoints even among independent unrelated families. CNV analysis was generally consistent between the two WGA methods. Translocation-specific PCR allowed us to detect each derivative chromosome in the MDA WGA samples but not with the LBA method, presumably due to coverage bias or the shorter sized WGA products. We successfully distinguished balanced reciprocal translocations from normal diploidy in normal samples with CNV analysis. A combination of CNV analysis and translocation-specific PCR using MDA-amplified WGA product can distinguish between balanced reciprocal translocation and normal diploidy in preimplantation genetic testing for structural rearrangements (PGT-SR).

Kabuki syndrome (KS) is characterized by growth impairment, psychomotor delay, congenital heart disease, and distinctive facial features. KMT2D and KDM6A have been identified as the causative genes of KS. Craniosynostosis (CS) has been reported in individuals with KS; however, its prevalence and clinical implications remain unclear. In this retrospective study, we investigated the occurrence of CS in individuals with genetically diagnosed KS and examined its clinical significance. Among 42 individuals with genetically diagnosed KS, 21 (50%) exhibited CS, with 10 individuals requiring cranioplasty. No significant differences were observed based on sex, causative gene, and molecular consequence among individuals with KS who exhibited CS. Both individuals who underwent evaluation with three-dimensional computed tomography (3DCT) and those who required surgery tended to exhibit cranial dysmorphology. Notably, in several individuals, CS was diagnosed before KS, suggesting that CS could be one of the clinical features by which clinicians can diagnose KS. This study highlights that CS is one of the noteworthy complications in KS, emphasizing the importance of monitoring cranial deformities in the health management of individuals with KS. The findings suggest that in individuals where CS is a concern, conducting 3DCT evaluations for CS and digital impressions are crucial.