Expanding the phenotype of UPF3B-related disorder: Case reports and literature review.

UPF3B encodes the Regulator of nonsense transcripts 3B protein, a core-member of the nonsense-mediated mRNA decay pathway, protecting the cells from the potentially deleterious actions of transcripts with premature termination codons. Hemizygous variants in the UPF3B gene cause a spectrum of neuropsychiatric issues including intellectual disability, autism spectrum disorder, attention deficit hyperactivity disorder, and schizophrenia/childhood-onset schizophrenia (COS). The number of patients reported to date is very limited, often lacking an extensive phenotypical and neuroradiological description of this ultra-rare syndrome. Here we report three subjects harboring UPF3B variants, presenting with variable clinical pictures, including cognitive impairment, central hypotonia, and syndromic features. Patients 1 and 2 harbored novel UPF3B variants-the p.(Lys207*) and p.(Asp429Serfs*27) ones, respectively-while the p.(Arg225Lysfs*229) variant, identified in Patient 3, was already reported in the literature. Novel features in our patients are represented by microcephaly, midface hypoplasia, and brain malformations. Then, we reviewed pertinent literature and compared previously reported subjects to our cases, providing possible insights into genotype-phenotype correlations in this emerging condition. Overall, the detailed phenotypic description of three patients carrying UPF3B variants is useful not only to expand the genotypic and phenotypic spectrum of UPF3B-related disorders, but also to ameliorate the clinical management of affected individuals.

The crucial role of titin in fetal development: recurrent miscarriages and bone, heart and muscle anomalies characterise the severe end of titinopathies spectrum.

BACKGROUND: Titin truncating variants (TTNtvs) have been associated with several forms of myopathies and/or cardiomyopathies. In homozygosity or in compound heterozygosity, they cause a wide spectrum of recessive phenotypes with a congenital or childhood onset. Most recessive phenotypes showing a congenital or childhood onset have been described in subjects carrying biallelic TTNtv in specific exons. Often karyotype or chromosomal microarray analyses are the only tests performed when prenatal anomalies are identified. Thereby, many cases caused by TTN defects might be missed in the diagnostic evaluations. In this study, we aimed to dissect the most severe end of the titinopathies spectrum. METHODS: We performed a retrospective study analysing an international cohort of 93 published and 10 unpublished cases carrying biallelic TTNtv. RESULTS: We identified recurrent clinical features showing a significant correlation with the genotype, including fetal akinesia (up to 62%), arthrogryposis (up to 85%), facial dysmorphisms (up to 73%), joint (up to 17%), bone (up to 22%) and heart anomalies (up to 27%) resembling complex, syndromic phenotypes. CONCLUSION: We suggest TTN to be carefully evaluated in any diagnostic process involving patients with these prenatal signs. This step will be essential to improve diagnostic performance, expand our knowledge and optimise prenatal genetic counselling.

Inferring disease course from differential exon usage in the wide titinopathy spectrum.

OBJECTIVE: Biallelic titin truncating variants (TTNtv) have been associated with a wide phenotypic spectrum, ranging from complex prenatal muscle diseases with dysmorphic features to adult-onset limb-girdle muscular dystrophy, with or without cardiac involvement. Given the size and complexity of TTN, reaching an unequivocal molecular diagnosis and precise disease prognosis remains challenging. METHODS: In this case series, 12 unpublished cases and one already published case with biallelic TTNtv were collected from multiple international medical centers between November 2022 and September 2023. TTN mutations were detected through exome or genome sequencing. Information about familial and personal clinical history was collected in a standardized form. RNA-sequencing and analysis of TTN exon usage were performed on an internal sample cohort including postnatal skeletal muscles, fetal skeletal muscles, postnatal heart muscles, and fetal heart muscles. In addition, publicly available RNA-sequencing data was retrieved from ENCODE. RESULTS: We generated new RNA-seq data on TTN exons and identified genotype-phenotype correlations with prognostic implications for each titinopathy patient (whether worsening or improving in prenatal and postnatal life) using percentage spliced in (PSI) data for the involved exons. Interestingly, thanks to exon usage, we were also able to rule out a titinopathy diagnosis in one prenatal case. INTERPRETATION: This study demonstrates that exon usage provides valuable insights for a more exhaustive clinical interpretation of TTNtv; additionally, it may serve as a model for implementing personalized medicine in many other genetic diseases, since most genes undergo alternative splicing.

Counseling and prenatal diagnosis in facioscapulohumeral muscular dystrophy: A retrospective study on a 13-year multidisciplinary approach.

Background and Aims: This is the first national population-based report about prenatal diagnosis for families with a history of facioscapulohumeral muscular dystrophy (FSHD), a complex hereditary disease. The incomplete disease penetrance and the phenotypic heterogeneity observed in carriers of D4Z4 alleles of reduced size, the FSHD molecular hallmark, make the estimate of genetic risk problematic. Methods: We considered all requests of preconception counseling and prenatal diagnosis received between January 2008 and December 2020 by the genetic counseling service associated with the Italian National Registry for FSHD (INRF). A multidisciplinary team managed the clinical and molecular data of each family. Results: Between 2008 and 2020, 60 couples required preconception counseling (PC) for FSHD. In 52 couples was observed at least one partner carried a D4Z4 reduced allele (DRA). Out of these 52 couples, 47 had a follow-up visit routine yearly. Out of these 47, 26 (55.3%) couples had children: eight asked for prenatal diagnosis (PND), two had assisted reproduction by heterologous in vitro fertilization (IVF), and 16 did not require further assistance. Regarding PND, 50 prenatal analyses were performed for 36 couples. The test resulted positive in 27 pregnancies, 12 (44.4%) were terminated, and 15 (55.6%) were carried to term. Conclusion: The different choices made by the couples show the importance of an integrated approach to support genetic counseling for FSHD. These results remark the relevance of the clinical and molecular investigation of the extended family, preferably before conception.