# Towards Next-Generation Sequencing as a First-Tier Diagnostic Test for Fructose-1,6-Bisphosphatase Deficiency

## TL;DR

Next-generation sequencing can quickly and accurately diagnose fructose-1,6-bisphosphatase deficiency, a rare but treatable metabolic disorder, especially in populations where it is common.

## Contribution

Demonstrates the effectiveness of first-tier next-generation sequencing in diagnosing FBP1 deficiency and identifying molecular profiles in high-prevalence populations.

## Key findings

- Two patients diagnosed within a month via exome sequencing had excellent outcomes after six years.
- A third patient, undiagnosed for 10 years, developed neurological complications.
- Exon 2 deletion in FBP1 was identified as a founder mutation in two cases.

## Abstract

Background: Advances in genomic technologies combined with tandem mass newborn screening have enabled early detection and management of several common inborn errors of metabolism. Fructose-1,6-bisphosphatase deficiency, an autosomal recessive treatable disorder reported in around 150 patients worldwide, remains underdiagnosed despite an excellent prognosis with early detection. Although common in highly consanguineous populations, diagnosis is often delayed due to the non-specific clinical and biochemical profile. Methods: This report explores the diagnostic pathway using first-tier next-generation sequencing of three novel cases of fructose-1,6-bisphosphatase deficiency in a tertiary care center in Lebanon. Results: Two patients were diagnosed with first-tier exome sequencing within one month of presentation and had an excellent outcome at 6 years of follow-up. The third patient, undiagnosed for 10 years, suffered from neurological sequalae. The molecular profile was remarkable in two patients for exon 2 deletion in the FBP1 gene, a founder mutation reported in Turkish and Armenian patients, and a rare frameshift mutation in the third case. Conclusions: The use of next-generation sequencing as as a first-tier test for FBP deficiency is a non-invasive and rapid method for early diagnosis and management of this rare yet treatable disorder. It can detect both disease-causing variants and large deletions, founder mutations as well, delineating the molecular profile in populations where this disorder is highly prevalent.