Next-Gen Cytogenetics Enters Clinical Care and Annotates the Human Genome

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The complexity of identification of pathogenic variants

Publication . Fino, Joana; David, Dezso

Introduction: Natural occurring genomic variant, from single nucleotide to balanced, unbalanced and complex rearrangements, spanning large chromosomal regions, has been reported to cause human pathologies. As such, we present cases with neurodevelopmental disorder, infertility, and recurrent miscarriage, which reflect the complexity of the identification of pathogenic variants, considering the variation spectrum, the underlying pathogenic mechanisms, and the heterogeneous clinical presentations. Methods: Long and small insert genomic sequencing (GS) was applied to four cases. Variants were identified from GS data mapped against the reference human genome and confirmed through Sanger sequencing. Results were interpreted using SVInterpreter, Exomiser, genotype-phenotype correlation and convergent genomic data analysis. Results: Although the first case is a carrier of a t(17;19)(p13.1;p13.3)mat, disrupting GSG1L2, and of a presumably paternally inherited dup(2)(q14.3q21.1), encompassing the autosomal dominant (AD) phenotype-associated PROC and HS6ST1 genes, the identified novel frameshift c.4442del, p.(Gly1481Valfs*21) variant of CHD4, was considered the disease-causing variant, since the proband’s phenotype fits the CHD4-associated Sifrim-Hitz-Weiss syndrome (Da Silva et al., 2022). Cases 2 and 3 were both reported with infertility, and carriers of t(5;9)(q31.3;p13) and t(4;21)(p14;q21.3), respectively. Our study revealed that the phenotype most plausibly resulted from a chromosomal position effect over YIPF5 and SPATC1L. The last case, presented intellectual disability and recurrent miscarriage, associated to t(7;22)(p13;q13.1). The 7p13 breakpoint disrupts the brain specific CAMK2B, causing AD mental retardation 54 (OMIM #617799), whereas increased meiotic segregation of der(22), during gametogenesis, most likely explain the reported miscarriage (David et al., 2023). Conclusions: These cases highlight the intricacy of pathogenic mechanisms leading to human disorders, the necessity for identification and evaluation of the “full” spectrum of genomic and genetic variants, of comparative reverse phenotyping, including patients with pathogenic variants affecting the same genes. Finally, highlight the need of introducing a more precise genomic medicine in clinical practice. This research was supported by FCT—Fundação para a Ciência e a Tecnologia, Research Grant HMSP-ICT/0016/2013 of the Harvard Medical School—Portugal Program.

2023-11-17Conference object

Open access

Funding agency

Fundação para a Ciência e a Tecnologia

Funding programme

Concurso de Projetos de IC&DT no âmbito do Acordo de Cooperação entre Portugal e a Harvard Medical School - 2013 / Investigação Clínica e de Translação

Funding Award Number

HMSP-ICT/0016/2013