The literature has already reported a form of mitochondrial myopathy in the newborn, which has the particularity of being self-limiting. This improvement is related to the transient nature of the respiratory chain deficit observed in these young children. This entity is listed as such with the acronym RIRCD for Reversible Infantile Respiratory Chain Deficiency), however, this case remains exceptional among mitochondrial diseases. Until recently, RIRCD was the preserve of mutations in mitochondrial DNA alone. But nuclear mitochondrial genes may be involved, most often in association with homoplasmic mutations in the dominant mitochondrial DNA (such as m.14674T).
In an article published in February 2021, Brazilian clinicians in collaboration with the English Reference Center for Mitochondriopathies report in detail the clinical, histological and genetic data of two children in whom the diagnosis of RIRCD was made in the neonatal period due to major hypotonia. In one child, a heterozygous variant of the nuclear QRSL1 gene was identified and in the other child, it was a variant of the nuclear gene EARSD2. Clinical improvement was gradual over several months despite significant fatty involution of muscle tissue in one of the patients. The authors stress the need to make the diagnosis early, to be proactive, and to wait at least six months, the time necessary to observe a full recovery.