# A rare case of mosaic partial tetrasomy 18p presenting with oligomenorrhea and intellectual disability: a case report

## TL;DR

This paper reports a rare case of a 17-year-old girl with mosaic tetrasomy 18p, a chromosomal disorder, who presented with irregular menstrual cycles and intellectual disability.

## Contribution

This is the first reported case of mosaic tetrasomy 18p in a 17-year-old female, highlighting novel clinical features like palm without fingerprints and oligomenorrhea.

## Key findings

- The patient had a chromosomal karyotype of 47,XX,+i(18)(p10)[85]/46,XX[15], indicating a mosaic duplication of 18p.
- Oligomenorrhea, distinctive physical features, and intellectual disability were associated with the chromosomal duplication.
- Combined use of G-banding, C-banding, and CNV-seq helped confirm the diagnosis and identify a 14.86 Mb duplication on 18p.

## Abstract

Tetrasomy 18p syndrome is an extremely rare chromosomal disorder that is often the result of an additional isochromosome for the short arm of chromosome 18. Most cases result from de novo mutations, although familial cases have also been reported. In this article, we report for the first time a case of a 17-year-old female patient with mosaic tetrasomy 18p.

This study aimed to investigate the genetic and clinical characteristics of patients with tetrasomy 18p and to enhance the understanding of tetrasomy 18p.

A female patient presenting with oligomenorrhea, distinctive physical features, and intellectual disability underwent chromosomal karyotype analysis via G-, C-, and N-banding techniques. Upon the detection of abnormal results, high-throughput genomic copy number variation sequencing (CNV-seq) was performed to establish a definitive diagnosis. Additionally, chromosomal karyotype analysis was conducted on both parents and the patient’s three younger sisters.

The G-banding karyotype results indicated 47,XX,+mar[85]/46,XX[15], suggesting a mosaic condition with one additional marker chromosome. C-banding revealed one centromere on the small marker chromosome, whereas N-banding revealed no satellite. CNV-seq analysis revealed a 14.86 Mb mosaic duplication spanning 18p11.32-p11.21, with an estimated copy number of 3.5. On the basis of these findings, the final chromosomal karyotype was designated 47,XX,+i(18)(p10)[85]/46,XX[15]. No chromosomal abnormalities were identified in the karyotypes of the patient’s parents or three sisters, indicating that this is a de novo mutation.

The patient’s oligomenorrhea, distinctive features, and intellectual disability may be associated with a partial duplication of the short arm of chromosome 18. Previous reports on patients with tetrasomy 18p have focused primarily on preschool or prepubescent patients. Here, we present the first reported case of a 17-year-old female with mosaic tetrasomy 18p. The absence of fingerprints on the palms and oligomenorrhea may represent novel characteristics of this condition. For such rare chromosomal abnormalities, the combined use of G-banding, C-banding karyotype analysis, CNV-seq technology, and comprehensive clinical evaluation can facilitate early diagnosis, genetic counseling, and personalized treatment.