LHON spectrum disorder: Phenotype and genes

Abstract

Leber hereditary optic neuropathy (LHON) is an inherited optic neuropathy primarily affecting young male with subacute bilateral visual loss. Clinically it is characterized by central scotoma, discromatopsia, and usually permanent central visual loss.This disease has a typical optic disc appearance at fundus examination of pseudoedema and microangiopathy which characterize the asymptomatic and subacute phases of the disease. Optic disc atrophy follows in the chronic phase.When the disease manifests, the preferential involvement of papillomacular fibres and macular retinal ganglion cell (RGC) damage are evident. These clinical features combined with the ophthalmoscopic pattern create the framework that make the disease unique.Primary point mutations of mitochondrial DNA (mtDNA) have been described as the genetic cause of the disease in about 90% of cases. Recently, new autosomal recessive DNA mutations have been reported in patients affected by subacute visual loss associated with a clinical picture resembling LHON.We herein describe the phenotype of 6 patients in which whole‐exome sequencing identified variants in the MECR gene in 2 probands of the same pedigree, in the NDUFAF4 gene in one patient, and mutation in the nuclear gene DNAJC30 in 3 patients. The 3 male probands with DNAJC30 mutation presented the typical LHON clinical picture with subacute loss of vision at an adult age in 2 cases and at a childhood age in one case. The pattern of visual loss with central scotoma and discromatopsia was associated with pseudoedema and microangiopathy at fundus appearance. Optical coherence tomography (OCT) analysis showed in both acute and asymptomatic family members the swelling of fibres while in the dynamic and chronic stages a progressive thinning of fibres. Visual recovery was detected in the younger patient and, partially, in one of adult patient.The 3 other patients carrying the MECR and NDUFAF4 gene variants showed a particular course of the disease characterized by a childhood onset of visual loss followed by a recurrence of visual loss at an adult age. The childhood onset was insidious in one case and subacute in the other 2 cases (about 6 years of age).OCT analysis demonstrated in the insidious case the temporal thinning of fibres and the macular RGC atrophy followed by swelling of fibres during the recurrence.In the differential diagnosis of inherited optic neuropathies with clinical presentation resembling LHON we should take into consideration the recessive form with mutations in the DNAJC30 gene which appears to overlap the mtDNA LHON disease. Moreover, clinical patterns resembling LHON with recurrence of visual loss represent another form of LHON with unique clinical presentation associated with variants in the MECR and the NDUFAF4 genes. These new clinical and genetic patterns enlarge the spectrum of LHON disease.