Genetic analysis of a child with restricted cardiomyopathy and phenylketonuria and a literature review

Abstract

To analyze the clinical and genetic characteristics of a child with restricted cardiomyopathy (RCM) and phenylketonuria (PKU), and summarize the clinical characteristics and genetic diversity of RCM in children through a literature review. A child with RCM in conjunct with PKU who was admitted to the Children's Hospital Affiliated to Zhengzhou University in June 2020 due to edema of eyelids and lower limbs for 1 year and aggravation for over 1 month was selected as the study subject. Relevant clinical data were collected. Peripheral blood samples of the child and his parents were collected for whole exome sequencing (WES). Candidate variants were validated by Sanger sequencing and bioinformatic analysis. Childhood, TNNI3 gene and restricted cardiomyopathy were used as the keywords to search the Wanfang data knowledge service platform, Chinese Journal Full-text database and PubMed database, and the search period was limited to from the time of establishment till August 2022. Clinical manifestations and characteristics of the TNNI3 gene variants were summarized. The child, a 2-year-old-and-4-month-old male, had normal intelligence, facial features and normal hair and skin color, but his motor and physical development was delayed, in addition with edema of bilateral eyelids and lower limbs. The results of WES and Sanger sequencing revealed that he has harbored compound heterozygous variants of the PAH gene, namely c.331C>T (p.R111X) and c.940C>A (p.P341T), which were inherited from his father and mother, respectively. In addition, he has also harbored a de novo heterozygous variant of c.508C>T (p.R170W) of the TNNI3 gene. Based on the guidelines from the American College of Medical Genetics and Genomics (ACMG), the TNNI3: c.508C>T (p.R170W) was classified as a pathogenic variant (PS2+PS4+PM2_Supporting+PM5), PAH: c.331C>T (p.R111X) as a pathogenic variant (PVS1+PM2_Supporting+PM3+PP4), and c.940C>A (p.P341T) as a likely pathogenic variant (PM2_Supporting+PM3+PM5+PP4). In total 30 children with RCM caused by TNNI3 gene variants were retrieved, with a male-to-female ratio of 1 : 1.55 and manifestations including heart failure, sinus rhythm, bi-atrial enlargement, ST-T wave change, ventricular restricted filling, and decreased ventricular diastolic function. In total 16 variants of the TNNI3 gene were identified, among which c.575G>A was the most common, and all cases had conformed to an autosomal dominant inheritance. Phenylalanine hydroxylase deficiency and RCM are rare diseases with complex clinical manifestations. The PAH: c.331C>T (p.R111X)/c.940C>A (p.P341T) and TNNI3: c.508C>T (p.R170W) variants probably underlay the RCM and PKU in this child.