PMC7390877_01
PMC7390877_02
Pedigree of the three-generation family of the patient 2. Generations are shown as I to III. Males are indicated by squares, females by circles, affected members by a shaded black square or circles and the proband by an arrow. Shaded black square with slash indicates death.
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F1
Analysis of the pedigree disclosed a marked family history of an X-linked maternal inheritance in the family of patient 2 (Figure 1).
Whole-exome sequencing (WES) paired-end reads are loaded in the IGV genome browser and are shown for each patient. (A) The heterozygous mutation, c.365A>T, in patient 1. (B) The heterozygous mutation, IVS7+1G>A, in patient 2. (C) Location of the point mutations in the OTC gene.
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F2
We found a novel missense mutation, c.365A>T, in exon 4 of the OTC gene in patient 1 (Table 1 and Figures 2A,C) and a reported splice site mutation, IVS7+1G>A, in intron 7 of the OTC gene in patient 2 (Table 1 and Figures 2B,C).
Mutations in the OTC gene in the two families. Pedigrees of the two families show the affected (solid), unaffected (open), and asymptomatic carrier (circle with dot) members. Squares, males; circles, females; slashed symbol, deceased. The genotype is shown underneath each symbol; WT, wild-type. (A) Patient 1 and her mother carried a novel heterozygous missense mutation, c.365A>T (p.Glu122Val), in exon 4. Multiple-sequence alignment of the amino acid sequences of OTC from different species revealed a complete conservation of the p.Glu122 residue across species (red box). (B) Identification of a mutation, IVS7+1G>A, in the OTC gene in the family of patient 2. The results showed a maternal carrier, while the father and sister were normal. The GenBank reference sequences of the human OTC gene are NM_000531.6 for the mRNA sequence and NC_000023.11 for the exon-intron boundary.
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F3
Sanger sequencing (Figure 3). Such molecular investigation supports a definitive diagnosis for the two patients with OTCD. The amino acid sequences of OTC from human and other species were compared to identify the conservation at the mutant position. A glutamate residue at the position 122 was completely conservative among distinct species (Figure 3A). IVS7+1G>A mutation was heterozygous in patient 2 (Figure 3B). IVS7+1G>A may affect normal splicing of exon 7.