Microduplication and Microdeletion Syndromes Diagnosed Prenatally Using Single Nucleotide Polymorphism Array.

We present a series of microdeletion and microduplication syndromes (MMSs) observed in our clinical practice over a three-year period from 2020 to 2023. Microdeletion and microduplication syndromes, characterized by chromosomal deletions or duplications of less than five megabases, pose challenges in terms of diagnosis, especially prenatal and clinical management. Clinically, MMSs encompass a broad spectrum of manifestations, ranging from intellectual disability and developmental delays to congenital anomalies, facial dysmorphisms, and neurobehavioral abnormalities. Notable examples include well-characterized syndromes such as DiGeorge syndrome (22q11.2 deletion), Prader-Willi syndrome (15q11-q13 deletion), and Williams syndrome (7q11 deletion). Our study focuses on the genetic foundations and prenatal ultrasound findings of these syndromes, with an emphasis on cases associated with intellectual disability. Using SNP array technology, we delve into the evolving landscape of diagnostic methods, providing a nuanced understanding of copy number variations (CNVs) and their implications. Prenatal diagnosis allows for the early detection of MMSs, enabling parents and healthcare providers to make informed decisions about the pregnancy and plan for appropriate medical care and interventions. Beyond theoretical considerations, our article bridges the gap between research and practical application by offering insights derived from clinical cases. Through the presentation of specific cases, we aim to contribute valuable data to the broader discourse on MMSs, fostering knowledge exchange and enhancing the medical community's awareness of these complex genetic conditions.

Challenging diagnoses of tetraploidy/diploidy and trisomy 12: utility of first-tier prenatal testing methods.

Introduction: Chromosome mosaicism and low-grade mosaicism present a challenge for diagnosis in the era of SNP array and NGS. Tetraploidy is a rare numerical chromosomal abnormality characterized by the presence of four copies of each chromosome. The prevalence of tetraploidy/diploidy mosaicism cases is extremely rare in the human population. Accurate estimates of the frequency of this chromosomal anomaly are lacking due to its classification as an extremely rare and difficult-to-detect condition. Methods: In this report, we describe two cases involving challenging diagnoses of tetraploidy/diploidy and trisomy 12. We utilized advanced genetic testing techniques, including SNP array, to examine the chromosomal abnormalities in these cases. We compared the results from SNP array to conventional G band karyotyping to assess the utility of first-tier prenatal testing methods. Results:Our analysis revealed two cases of tetraploidy/diploidy and trisomy 12 with atypical presentations. SNP array analysis provided higher resolution and more precise information about the chromosomal anomalies in these cases compared to conventional G band karyotyping. Additionally, the prevalence of tetraploidy/diploidy mosaicism was confirmed to be extremely rare in the population. Discussion: Low-level mosaicism is difficult to diagnose, and in many cases, it has traditionally been identified through techniques such as G band karyotype or FISH. Microarray has become an invaluable diagnostic tool for detecting chromosomal abnormalities, offering high-resolution insights. However, it may not always be able to detect rare occurrences of tetraploidy or tetraploidy/diploidy mosaicism. As a result, it is recommended to perform a G band karyotype analysis after obtaining a negative microarray result before considering other diagnostic methods with a potentially higher yield of diagnosis. For the detection of low-level mosaicism, combined diagnostic methods should be considered. The diagnosis of mosaicism is a multistep process that can be time-consuming, often requiring the application of more than one diagnostic technique. This approach is crucial for accurate diagnosis and comprehensive patient care. Further research is warranted to better understand the underlying mechanisms of these rare chromosomal anomalies and to develop more effective diagnostic strategies for challenging cases.

Genetic testing in patients with global developmental delay / intellectual disabilities. A review.

Genetic factors are responsible for up to 40% developmental disability cases, such as global developmental delay/intellectual disability (GDD/DI). The American and more recently the European guidelines on this group of diseases state that genetic testing is essential and should become a standardized diagnostic practice. The main arguments for the necessity of implementing such a practice are: (1) the high prevalence of developmental disabilities (3% of the population); (2) the high genetic contribution to this type of pathology; (3) insufficient referral for genetic consultation. In an attempt to address these issues, the purpose of this paper is to present the genetic etiology of global developmental delay / intellectual disability with emphasis on the need to implement a genetic testing protocol for the patients with GDD/DI, as indicated by the current guidelines. Chromosomal abnormalities and fragile X syndrome are the most frequent causes of developmental disabilities and the techniques employed to detect such genetic disorders should be used as first line investigations of GDD/DI.