# A 30-Year Experience in Fragile X Syndrome Molecular Diagnosis from a Laboratory in Thailand

## TL;DR

This study shares 30 years of experience in diagnosing Fragile X syndrome in Thailand, finding it affects about 7% of individuals with intellectual disability.

## Contribution

The study provides the largest series of FXS molecular testing in Thailand and emphasizes prenatal testing and genetic counseling.

## Key findings

- Full mutations in FXS were found in 7.2% of males and 3.3% of females tested.
- No premutation alleles were found in the index cases, but two males were suspected to have FMR1 gene deletions.
- Approximately 7% frequency of FXS was identified in different Thai patient cohorts over 30 years.

## Abstract

Fragile X syndrome (FXS) is the most common form of X-linked intellectual disability (ID). This study aimed to share 30 years of experience in diagnosing FXS and determine its frequency in Thailand. We retrospectively reviewed 1480 unrelated patients (1390 males and 90 females) with ID, developmental delay, or autism spectrum disorder, or individuals referred for FXS DNA testing at Songklanagarind Hospital, Thailand, over a 30-year period. The samples were analyzed using cytogenetic methods, PCR-based techniques, and/or Southern blot analysis. Full mutations (>200 CGG repeats) were identified in 100 males (7.2%) and three females (3.3%). An intermediate allele was detected in one male, while no premutation was found in the index cases. Two males were suspected to have FMR1 gene deletions. Twelve families underwent prenatal testing during this study. Most families undergoing prenatal FXS diagnosis involved mothers who were premutation carriers and had given birth to children affected by FXS. This study represents the largest series of molecular genetic FXS testing cases reported in Thailand. The frequency of FXS identified in different cohorts of Thai patients across various periods was approximately 7%. This study enhances public awareness of at-risk populations and highlights the importance of prenatal testing and genetic counseling for vulnerable families.