# Ultra-rare monogenic disorders frequently detected among sex chromosome aneuploidy patients with atypical findings

## TL;DR

Some children with sex chromosome aneuploidies also have rare genetic disorders, which can be missed if not tested for.

## Contribution

The study shows that a significant proportion of SCA patients with atypical symptoms have co-occurring ultra-rare monogenic disorders.

## Key findings

- 22.2% of SCA patients showed atypical symptoms, and 41.7% of these had a confirmed monogenic disorder.
- Five distinct ultra-rare monogenic disorders were identified in the study cohort.
- Diagnostic delays were observed, with SCA diagnosed at 3.5 months versus 7.0 years for the second genetic condition.

## Abstract

Sex chromosome aneuploidies (SCA) such as Turner, Klinefelter, Jacobs, and Trisomy X syndromes are prevalent genetic disorders with well-established phenotypes. Challenges persist, however, in determining the need for further genetic evaluation in cases of affected individuals exhibiting atypical symptoms. The present study retrospectively examined 54 pediatric patients with an SCA diagnosis at a single institution between January 2015 and December 2023. Twelve patients (22.2%) exhibited a discordant phenotype, of which five were confirmed to have a distinct monogenic disorder, a diagnostic rate of 41.7%. The monogenic conditions identified included DNAH5-related primary ciliary dyskinesia, Burn-McKeown syndrome, Tatton-Brown-Rahman syndrome, SETD1B-related neurodevelopmental disorder, and SET-related disorder. The median age at SCA diagnosis was 3.5 months versus 7.0 years for the second genetic condition, indicating significant diagnostic delays. Our findings highlight the importance of comprehensive genetic evaluation in pediatric patients with SCA who exhibit atypical phenotypes.