Deep intronic TIMMDC1 variant delays diagnosis of rapidly progressive complex I deficiency

M. Naber, D. Hellebrekers, R.A.J. Nievelstein, P.M. van Hasselt, R.H. van Jaarsveld, I. Cuppen, R. Oegema*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

1 Citation (Web of Science)


Complex I deficiency is the most common pediatric mitochondrial disease. It can cause a wide range of clinical disorders, including Leigh syndrome. TIMMDC1 encodes an assembly protein of complex I and has been recently associated with early onset mitochondrial disease in three unrelated families. In all three families the same homozygous deep intronic variant was identified leading to inclusion of a new exon resulting in a frameshift and premature stop codon (c.596 + 2146A > G, p.Gly199_Thr200ins5*). Herein, we describe two brothers of Dutch descent, presenting in infancy with hypotonia and respiratory insufficiency and a rapidly progressive and fatal disease course. Laboratory findings and metabolic investigations revealed no specific abnormalities, notably no raised plasma lactate. MRI showed transient lesions in the basal ganglia of brother 1. A muscle biopsy demonstrated complex I deficiency in brother 2. Exome sequencing yielded a novel heterozygous TIMMDC1 variant: c.385C > T, p.(Arg129*). Targeted sequencing revealed the previously published deep intronic variant c.596 + 2146A > G, p.(Gly199_Thr200ins5*) on the second allele which is not detected by exome sequencing. In summary, we present the fourth family with TIMMDC1-related disease, with a novel nonsense variant. This report illustrates the importance of considering mitochondrial disease even when laboratory findings are normal, and the added value of targeted sequencing of introns.
Original languageEnglish
Article number104120
Number of pages5
JournalEuropean Journal of Medical Genetics
Issue number1
Publication statusPublished - 1 Jan 2021


  • children
  • complex 1 deficiency
  • genetics
  • intronic variant
  • leigh
  • mitchondrial disease
  • mitochondrial complex
  • timmdc1
  • Complex 1 deficiency
  • Genetics
  • Mitchondrial disease
  • Intronic variant

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