# A Novel Homozygous Missense Variant of PIGT Related to Multiple Congenital Anomalies-Hypotonia Seizures Syndrome 3 with Elevated of Serum ALP Level in a Thai Newborn Patient

## TL;DR

A Thai newborn with a rare genetic disorder had a new PIGT gene mutation linked to severe symptoms and high ALP levels.

## Contribution

Reports the first Thai case of MCAHS3 with a novel PIGT variant and elevated ALP, expanding the syndrome's clinical understanding.

## Key findings

- A novel homozygous PIGT c.257A>G (p.His86Arg) variant was identified in a Thai MCAHS3 patient.
- Reduced CD59 expression suggests impaired GPI-AP synthesis due to the PIGT mutation.
- Elevated ALP levels indicate a late-stage GPI synthesis defect in this MCAHS3 case.

## Abstract

Phosphatidylinositol glycan class T (PIGT) is part of the glycosylphosphatidylinositol transamidase (GPI-TA) complex, crucial for various cell functions. Biallelic pathogenic variants in PIGT are associated with Multiple Congenital Anomalies-Hypotonia Seizures Syndrome 3 (MCAHS3), a rare neonatal hypotonia syndrome characterized by dysmorphic features and seizures. Diagnosing neonatal hypotonia, which has diverse congenital and acquired causes, is challenging, particularly in syndromic monogenic cases. Next-generation sequencing is essential for accurate diagnosis. This study reports a term newborn with hypotonia, dysmorphic features, seizures, and severe skeletal issues, including a humeral fracture at birth, consistent with MCAHS3. Trio whole exome sequencing (WES) analysis revealed a novel homozygous missense variant in PIGT, expanding the clinical spectrum of MCAHS3 and marking the first such case in the Thai population. The identified c.257A>G (p.His86Arg) variant manifests a severe MCAHS3 phenotype, as evidenced by reduced CD59 expression in western blot analysis, indicating impaired GPI-AP synthesis. Computational predictions suggest this mutation causes protein instability, potentially affecting GPI anchor attachment. While alkaline phosphatase (ALP), a GPI-AP crucial for skeletal mineralization, was elevated in this case, suggesting a late-stage GPI synthesis defect. The His86Arg mutation in PIGT may disrupt GPI-TA function, hindering proper protein attachment and leading to cleaved protein secretion. Further functional studies are needed to elucidate the impact of this mutation on PIGT function and MCAHS3 phenotypes.