Tessa et al. (2009) identified homozygosity for the p.R179X mutation in affected members of two unrelated families with HHH syndrome from Senegal and Morocco, respectively. In the Moroccan family, one child had onset in infancy of lethargy and coma, and later had liver involvement and coagulopathy, but the other child, who was homozygous for the p.R179X mutation, had no symptoms by age 4 years.

Korman et al. (2004) described two brothers with HHH Syndrome. Sequencing of the SLC25A15 gene identified a homozygous 446G deletion in exon 3 in both patients, which produced a frameshift leading to a premature stop codon in exon 4. Both parents, who were first cousins, were heterozygous for this mutation. In addition, both the affected siblings and their mother were found to be homozygous for a 760A>T SNP in exon 5. This change was also found in additional unrelated controls. The father was heterozygous for this polymorphism.

A novel homozygous mutation in the SLC25A15 gene was identified by Al-Hassnan et al. (2008) in three affected Saudi siblings with HHH syndrome. The mutation was a single base substitution, c.817G>A, resulting in p.Gly220Arg amino acid substitution, which alters the hydropathy status of the protein at this amino acid location. This mutation causes alterations in the protein's structure and function, and it was predicted to be pathogenic.