Aug 2026· Cytogenetic and Genome Research· pp.
1
· 0 citations
Medicine
TL;DR
A pedigree in which a neurotypical father transmitted AS to multiple offspring via a structural mechanism distinct from UPD is reported, highlighting the role of sSMCs in masking pathogenic deletions and underscores the diagnostic importance of high-resolution genomic mapping in cases of atypical imprinting transmission.
BACKGROUND
Non-mosaic Klinefelter syndrome (47,XXY) arises from sex-specific meiotic mechanisms leading to nondisjunction during gametogenesis. In maternal cases, errors occur predominantly during meiosis I, frequently involving X chromosomes that lack crossovers or exhibit crossovers outside optimal chromosomal locations; this nondisjunction is further exacerbated by advancing maternal age and the subsequent deterioration of cohesins. Conversely, paternal 47,XXY stems primarily from the failure of obligate recombination within the pseudoautosomal region, which is critical for accurate XY segregation.
OBJECTIVE
Drawing on the latest literature, this review transitions from a descriptive account of non-mosaic Klinefelter syndrome (nKS) toward a comprehensive analysis of mechanistic and genomic evidence, establishing a unified framework of sex-specific meiotic vulnerability.
METHODS
We synthesized recent findings from forward genetic approaches in mouse models with data from human observational and reverse-genetic studies, delineating an updated view of the established and putative mechanisms that modulate sex chromosome segregation.
RESULTS
We frame XX and XY nondisjunction as a genetically modulated process rather than a purely stochastic event. The integrated evidence supports a unified framework in which maternal and paternal mechanisms converge primarily on meiotic recombination failure but differ in timing, chromosomal context, and genetic modulation.
CONCLUSIONS
From a clinical standpoint, identifying the molecular drivers of sex chromosome aneuploidy will enhance genetic counseling and risk stratification. Such insights are poised to facilitate informed reproductive decision-making and timely therapeutic support, ultimately reducing the burden of nKS comorbidities and improving patients' quality of life.
Matteo Lampitto, Marco Barchi· Andrology· 0 citations
MEST is identified as a plausible candidate gene for SRS and provides a rationale for further functional studies, including in silico predictions and clinical correlation.
Xiaocha Xu, R. Pan, Shuai Chen et al.· Genes· 0 citations
Background: Although the balanced carriers of Robertsonian translocations (ROBs) typically exhibit normal phenotypes, they may experience recurrent abortions or have offspring with chromosomal disorders. A proposed mechanism is the inter-chromosomal effect (ICE), where disrupted meiotic segregation may increase aneuploid gamete production. This study presents a male case carrier of t(13;14) who had a deceased child with Down syndrome (DS) and investigates t(13;14) as a potential factor contributing to the birth of a child with DS. Case Presentation: A couple with a history of recurrent abortions and a deceased child with DS was referred to a medical genetics laboratory. Karyotype analysis revealed that the male partner was a carrier of t(13;14) (45,XY,t(13;14)), while the female partner had a normal karyotype. The couple’s subsequent pregnancy resulted in a healthy female fetus inheriting t(13;14). The deceased child had a karyotype of 47, XY, +21, consistent with DS. In this study, the role of t(13;14) and ICE as potential contributors to the birth of a child with DS was explored. Conclusion: Prenatal screening for carriers of ROBs is strongly recommended to assess the risk of unbalanced chromosomal disorders in offspring.
Sahra Sahraeean, Asiyeh Jebelli, Saeed Ghadimi Haddadan et al.· Journal of reproduction & in...· 0 citations
BACKGROUND
Complete androgen insensitivity syndrome (CAIS) is one of the most prevalent conditions of disorders/differences of sex development (DSD), with an X-linked recessive inheritance. A hemizygous pathogenic variant in the AR gene causes the condition.
CASE REPORT
We present a five-generation Czech family with several CAIS-positive relatives. The proband is a 27-year-old female patient with a 46,XY karyotype, who exhibits the typical CAIS phenotype. This includes female external genitalia, the absence of uterus, a blind-ending vagina, undescended testes, and almost missing axillary and pubic hair.
METHODS AND RESULTS
We identified a novel pathogenic, hemizygous NM_000044.4(AR):c.-66_220del p.? variant using Sanger DNA sequencing with specifically designed primers. This AR deletion was 286 bp in length and initiated in the 5'-UTR, terminating within the polymorphic CAG repeats in exon 1 of the AR gene. The AR variant removed the original initiation codon ATG, resulting in a shortened AR transcript with an unknown effect on the translation.
CONCLUSION
We describe a unique AR deletion identified in a 46,XY female patient with CAIS. The variant segregates in the large CAIS family; it was detected in five affected relatives, while the four remaining family members were asymptomatic carriers.
Júlia Martinková, Andrea Gřegořová, M. Wayhelova et al.· Biomedical papers of the Med...· 0 citations
Trisomy 21 (T21) is the most common genetic cause of intellectual disability, yet the molecular mechanisms underlying maternal meiosis I errors—responsible for ~70% of free T21 cases— remain poorly understood. In this preliminary study, we used long-read sequencing and genome assembly to investigate the DNA sequence and epigenetic features of chromosome 21 (chr21) centromeres in a family with recurrent free T21 due to maternal meiosis I errors. The mother, who had two affected and three unaffected children, showed no mosaicism or structural rearrangements. One of her two chr21 centromeres lacked a pronounced centromere dip region (CDR), displaying instead a diffuse hypomethylation pattern (dCDR) with much higher methylated CpG levels (55%) compared to its homologue (36%). This dCDR was transmitted to an unaffected child and the affected proband, suggesting it was present in one of the maternal chr21 since she was at least 32 years of age. Chr21 dCDRs were not observed in seven young mothers with children with T21 or previously described in the literature in 108 population haplotypes. We hypothesize that dCDRs may weaken kinetochore function, increasing nondisjunction risk, and propose two models linking such epigenetic variation to maternal age-related T21 risk. These findings highlight the value of complete centromere characterization in families with children with T21 and suggest centromere methylation status of chr21 as a potential T21 risk factor for future investigation.
F. K. Mastrorosa, K. Hoekzema, Marcelo Ayllon et al.· bioRxiv· 0 citations
Maternal uniparental disomy of chromosome 15 [UPD(15)mat] and imprinting defects account for about 30% of cases of Prader–Willi syndrome (PWS). Mosaic UPD(15)mat is rare and may escape routine testing. We describe a 45-year-old male patient in whom persistent clinical suspicion of PWS was not genetically confirmed by repeated methylation-based analyses. Clinical manifestations included neonatal hypotonia with low birth weight, early hyperphagia, severe obesity, short stature, growth hormone deficiency, type 2 diabetes mellitus, dyslipidemia, and MASLD/MASH with compensated cirrhosis. He presented with very mild neurodevelopmental impairment. Following the detection of proteinuria and microalbuminuria from age 22 years, focal segmental glomerulosclerosis was diagnosed upon renal biopsy. A family history of cerebrovascular events was recorded. Combined SNP-array and MS-MLPA analyses across tissues established a diagnosis of PWS due to mosaic UPD(15)mat. The mosaic fraction, estimated by SNP-array, was approximately 10% in peripheral blood and 40% in buccal cells; MS-MLPA detected abnormal methylation only in buccal cells, explaining the previous negative blood-based results. Exome sequencing identified the paternally inherited pathogenic NOTCH3 variant NM_000435.2:c.3016C>T, p.(Arg1006Cys). Subsequent brain MRI showed chronic vascular-type leukoencephalopathy consistent with CADASIL, despite the absence of overt ischemic events in the proband. Collectively, these investigations established a dual molecular diagnosis of PWS due to mosaic UPD(15)mat and NOTCH3-related CADASIL. This report highlights the pivotal role of clinical genetics in assessing the precise diagnosis in rare diseases. With respect to PWS, it demonstrates that mosaicism can lead to a missed diagnosis when the genetic investigation is limited to peripheral blood. In addition, following the diagnosis of CADASIL, and based on the available evidence linking NOTCH3 to renal physiology and disease, we discuss whether NOTCH3-related renal microangiopathy may have contributed to the renal phenotype. However, given the patient’s multiple renal risk factors, FSGS was considered most likely multifactorial, and a causal association with CADASIL cannot be established from this single case.
F. Bogliardi, Pino D’Ambrosio, Giorgia Quattromini et al.· Genes· 0 citations
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