A novel missense mutation in the UBE2A gene causes intellectual disability in the large X-linked family

A novel UBE2A splice site variant causing intellectual disability type Nascimento

X-linked intellectual disability type Nascimento (XLID) is a rare disease caused by variants in the ubiquitin-conjugating enzyme E2A gene (UBE2A). Patients with XLID have similar phenotypes, including speech impairments, severe intellectual disability, hearing loss, wide facies, synophrys, generalized hirsutism, and urogenital abnormalities. Till date, only two splice-site variants of the UBE2A gene have been observed in patients with X-linked ID type Nascimento. Here, we report the case of a Chinese boy with a syndrome clinically similar to XLID with speech impairment, severe intellectual disability, and moderate hearing loss. However, different characteristics were also present in the patient, including an inability to maintain his head in an upright posture. Both of the patient's palms have a single transverse palmar crease. Subsequent whole-exome sequencing revealed a novel splice site variant in UBE2A (c.241 + 1 G > A). Our study not only expands the variant spectrum and clinical characteristics of UBE2A deficiency syndrome but also provides clinical evidence for genetic diagnoses.

Phenotypes of Cornelia de Lange syndrome caused by non-cohesion genes: Novel variants and literature review

BACKGROUND

Cornelia de Lange syndrome (CdLS) is a genetic disorder caused by variants in cohesion genes including NIPBL, SMC1A, SMC3, RAD21, and HDAC8. According to the 2018 consensus statement, a patient with clinical scored ≥ 11 points could be diagnosed as CdLS. However, some variants in non-cohesion genes rather than cohesion genes can manifest as phenotypes of CdLS.

OBJECTIVES

This study describes six variants of non-cohesion genes (KDM6A, KMT2D, KMT2A ANKRD11, and UBE2A), and assesses the reliability of 11-points scale criteria in the clinical diagnosis of CdLS.

METHODS

Whole-exome sequencing (WES) was performed on six patients with features of CdLS. Phenotypic and genotypic spectra of 40 previously reported patients with features of CdLS caused by non-cohesion genes variants and 34 previously reported patients with NIPBL variants were summarized. Clinical score comparison among patients with NIPBL variants versus those with variants in non-cohesin genes was performed.

RESULTS

Variants in non-cohesion genes were found in six patients [KMT2A (n = 2), KMT2D, ANKRD11, KDM6A, and UBE2A]. Of them, four variants (KMT2A c.7789C > T, ANKRD11 c.1757_1776del, KDM6A c.655-1G > A, and UBE2A c.439C > T) were novel. Combining with previously reported cases, 46 patients with phenotypes of CdLS caused by variants in 20 non-cohesion genes are now reported. From this total cohort, the average clinical score of patients in ANKRD11 cohort, SETD5 cohort, and AFF4 cohort was statistically lower than those in NIPBL cohort (8.92 ± 1.77 vs. 12.23 ± 2.58, 7.33 ± 2.52 vs. 12.23 ± 2.58, 5.33 ± 1.53 vs. 12.23 ± 2.58; p < 0.05). The average clinical score of KMT2A cohort, EP300 cohort, and NIPBL cohort had not significantly different from (11 ± 2.19 vs. 12.23 ± 2.58, 10 ± 4.58 vs. 12.23 ± 2.58; p > 0.05).

CONCLUSION

We described 4 novel variants of non-cohesion genes in six Chinese patients with phenotypes of CdLS. Of note, three genes (KMT2D, KDM6A, and UBE2A) causing features of CdLS have never been reported. The proposed clinical criteria for CdLS needed to be updated and refined, insofar as WES was necessary to confirm the diagnosis of CdLS. Our study expanded the spectra of non-cohesion genetic variations in patients with features of CdLS.