Marlena Młynek

X-chromosome inactivation (XCI) is an epigenetic regulatory mechanism thatequalizes the expression of X-linked genes between the sexes. Although this processis physiological, it can become disrupted, leading to phenotypic variabilityin women who are carriers of X-linked recessive mutations. This paper reviewsthe mechanisms of XCI, the factors influencing the randomness of this processand its clinical significance in women. We present literature data on the variabilityof XCI patterns across different tissues and on diseases in which non-random inactivationpattern affects the clinical manifestation in women. The diagnostic valueof the HUMARA test and its limitations in routine XCI analysis are also discussed.

Objective: Copy number variants (CNVs) overlapping genes associated with neurodevelopmental disorders in patients with epilepsy are particularly concentrated in epilepsy hotspot loci. The aim of this study was to evaluate epilepsy as a component of the dysmorphic–neurodevelopmental phenotype in patients with recurrent CNVs. Methods: The study included genetic and clinical data from 177 pediatric patients carrying 17 recurrent CNVs showing well-documented enrichment in epilepsy or associated with genetic OMIM syndromes. Results: Epilepsy was diagnosed in 50 of 177 children (28.2%), developmental delay in 147 (83.0%), dysmorphic features in 104 (58.8%), behavioral problems in 62 (35.0%), and congenital anomalies in 55 (31.1%). Among recurrent CNV hotspots, the del16p11.2 BP4–BP5 deletion was the most frequent, occurring in 39 of 177 patients. Ten children (25.6%) with del16p11.2 presented with epilepsy as part of the phenotype. Other frequently represented CNVs included del15q11.2 BP1–BP2 (OMIM #615656; 19/177 patients, 4/19 with epilepsy), del1q21.1 (OMIM #612474; 15/177, 6/15 with epilepsy), del15q13.3 (OMIM #612001; 13/177, 4/13 with epilepsy), and dup16p11.2 (OMIM #614671; 12/177, 1/12 with epilepsy). The highest proportion of epilepsy as a phenotypic component was observed in patients with del1p36 (OMIM #607872; 6/9 patients) and del1q21.1 (OMIM #612474; 6/15 patients). Conclusions: Our data support the clinical utility of CNV testing in patients with epilepsy accompanied by additional neurodevelopmental or dysmorphic features, in line with current diagnostic guidelines. The epilepsy-plus phenotype may help clinicians identify patients who are most likely to benefit from CNV analysis.

Background: Rubinstein–Taybi syndrome (RSTS) is characterized by intellectual disability, short stature, distinctive facial dysmorphism, broad thumbs/halluces, hearing loss, congenital heart or renal defects, and cryptorchidism in males. Pathogenic variants in CREBBP (~90% of cases) or EP300 (~10%) underlie the disorder, with ~88% single nucleotide variants (SNVs) and ~12% copy number variants (CNVs) in CREBBP. Materials and Methods: We investigated 17 patients clinically diagnosed with RSTS at a tertiary hospital in Poland. Genetic confirmation was achieved by next-generation sequencing, multiplex ligation-dependent probe amplification (MLPA), array comparative genomic hybridization (aCGH), or Sanger sequencing. Results: Pathogenic variants were identified in CREBBP (13/17, 76%) and EP300 (4/17, 24%). Variant types included frameshift indels (6/17, 35%), missense (4/17, 24%), nonsense (3/17, 18%), splice-site (2/17, 12%), and gross deletions (2/17, 12%). Notably, 13/17 (76%) were novel: ten in CREBBP (c.−49_12del, c.289C>T, c.1093_1096del, c.1094A>G, c.3178A>T, c.3401A>T, c.(3836+1_3837−1)_(4394+1_4395−1)del, c.4133+2T>G, c.4963dup, c.5028_5029dup) and three in EP300 (c.1942C>T, c.3044_3045del, c.4713_4722del). Among the novel CREBBP variants, eight occurred de novo and two had unknown inheritance. Two novel EP300 variants occurred de novo and one was of unknown origin. Conclusions: This first Polish RSTS cohort demonstrates a considerable proportion of gross deletions (12% overall; 15% in CREBBP) and an unexpectedly high rate of novel variants (76%), suggesting possible population-specific differences. These findings underscore the genetic heterogeneity of RSTS and highlight the importance of comprehensive molecular diagnostics and studies in underrepresented populations.

Prenatal genetic diagnosis includes screening tests (to assess the risk of chromosomal aberrations) and diagnostic tests (to identify changes in DNA). The dynamic development of molecular methods in prenatal diagnosis has significantly expanded diagnostic possibilities, and techniques based on next-generation sequencing (NGS) are playing an increasingly important role. The wider availability and scope of prenatal tests contributes to early and more precise diagnosis and helps to improve a perinatal care and clinical management after birth. This article presents genetic techniques currently used in Poland in prenatal diagnosis and related current clinical guidelines.

Background: Mapping the breakpoints in de novo balanced chromosomal translocations (BCT) in symptomatic individuals provides a unique opportunity to identify in an unbiased way the likely causative genetic defect and thus find novel human disease candidate genes. Our aim was to fine-map breakpoints of de novo BCTs in a case series of nine patients. Methods: Shallow whole-genome mate pair sequencing (SGMPS) together with long-range PCR and Sanger sequencing. In one case (BCT disrupting BAHD1 and RET) cDNA analysis was used to verify expression of a fusion transcript in cultured fibroblasts. Results: In all nine probands 11 disrupted genes were found, that is, EFNA5, EBF3, LARGE, PPP2R5E, TXNDC5, ZNF423, NIPBL, BAHD1, RET, TRPS1 and SLC4A10. Five subjects had translocations that disrupted genes with so far unknown (EFNA5, BAHD1, PPP2R5E, TXNDC5) or poorly delineated impact on the phenotype (SLC4A10, two previous reports of BCT disrupting the gene). The four genes with no previous disease associations (EFNA5, BAHD1, PPP2R5E, TXNDC5), when compared with all human genes by a bootstrap test, had significantly higher pLI (pEFNA5, BAHD1 and PPP2R5E were particularly good candidates for novel disease loci. The pathomechanism for BAHD1 may involve deregulation of expression due to fusion with RET promoter. Conclusion: SGMPS in symptomatic carriers of BCTs is a powerful approach to delineate novel human gene–disease associations.

Sotos syndrome 2 (MIM #614753), known also as Malan syndrome, is caused by heterozygous mutations/deletions of the NFIX gene located on chromosome 19p13.2. It manifests in developmental delay, intellectual impairment, macrocephaly, central nervous system anomalies, postnatal overgrowth, and craniofacial dysmorphism. Unusual behavior with/without autistic traits, ophthalmologic, gastrointestinal, musculo-skeletal, and hand/foot abnormalities are also frequent. Due to the limited number of such cases, no definitive conclusions about genotype-phenotype correlations have been possible. In the following paper, we discuss physical features consistent with Sotos syndrome 2 based on literature review and two new cases [a patient with de novo 19p13.2 deletion encompassing a part of the NFIX gene and a patient with de novo (not described so far) heterozygous missense mutation c.367C>T (p.Arg123Trp) in the NFIX gene]. Apart from overgrowth and psychomotor developmental delay, the most consistent physical features of our two patients are dysmorphism including high forehead, downslanting palpebral fissures, pointed chin, and abnormalities of the pinna. Both show abnormal behavior and present with long, tapered fingers and toenail defect. No severe congenital malformations were noted. We hope these data will serve as a material for further studies and provide an opportunity to make more reliable genotype-phenotype correlations.