Whole-exome sequencing uncovered the 3-hydroxy-3-methylglutaryl-CoA lyase deficiency as the cause of lethal in a Vietnamese infant

Metabolic disorders are due to a deficiency of enzymes, which can severely impact health or cause serious complications without treatment. This study aimed to identify the molecular causes of an infant death who had been hospitalized with complicated health problems and metabolism syndrome. Whole-exome sequencing (WES) was used to screen pathogenic variants in the patient’s genome, followed by examination of variants segregation in her parents. The WES analysis identified two homozygous variants, c.[614C>G; 649A>G] in the HMGCL gene of the patient. These two variants co-locate within the exon 7 of the HMGCL gene, resulting in 2 amino acid substitutions, p.[T205S; M217V], in the conservative region of enzyme protein. Sanger sequencing showed that the patient’s unaffected mother and father carried one mutant allele of the HMGCL gene containing two c.[614C>G; 649A>G] variants. The HMGCL gene encodes the 3-hydroxy-3-methylglutaryl-CoA lyase enzyme, which is critical in the ketogenic pathway. The deficiency of this enzyme was reported to be a life-threatening illness in the neonatal period, and two variants detected in this study were also found in a Japanese patient with sudden, unexpected death in infancy. The frequency of these two variants in the Vietnamese in-hour database and their further functional analysis were also reported in this study. The results of this study have explored the molecular etiology that causes the severe, deadly condition of the patient and provide an understanding of the risk of disease in her family.