A novel HADHA variant associated with an atypical moderate and late-onset LCHAD deficiency

Abstract

Background: Long chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) is a rare inherited disease caused by pathogenic variants of HADHA gene. Along with signs common to fatty acid oxidation defects (FAOD), specific retina and heart alterations are observed. Because long-chain fatty acid oxidation is selectively affected, supplementations with short/medium-chain fats represent energetic sources bypassing the enzymatic blockade. Here, we report on an atypical presentation of the disease.

Methods: Clinical features were described with medical explorations including ophthalmic and cardiac examination. Biological underlying defects were investigated by measurements of biochemical metabolites and by fluxomic studies of mitochondrial β-oxidation. Whole exome sequencing and molecular validation of variants confirmed the diagnosis.

Results: The patient has developed at nine years an unlabeled maculopathy, and at 28 years, an acute cardiac decompensation without any premise. Blood individual acylcarnitine analysis showed a rise in hydroxylated long-chain fatty acids and fluxomic studies validated enzyme blockade consistent with LCHADD. Genetic analysis revealed the common p.(Glu510Gln) variant in HADHA, in trans with a novel variant c.1108G > A, p.(Gly370Arg) located in the NAD binding domain. Patient pathology was responsive to triheptanoin supplementation.

Conclusion: This atypical LCHADD form report should encourage the early assessment of biochemical and genetic testing as a specific management is recommended (combination with fast avoidance, low fat-high carbohydrate diet, medium-even-chain triglycerides or triheptanoin supplementation).

Keywords: Atypical maculopathy; Cardiomyopathy; HADHA; LCHAD; Late-onset; Mitochondrial trifunctional protein MTP.

Fig. 1

Individual acylcarnitine analyses in the patient. A. Diagnostic serum acylcarnitine non-fluxomic profile. Acylcarnitines were directly assayed in serum from the patient without any prior added substrate or incubation. Acylcarnitine from the patient are written in blue, and corresponding internal standards are indicated in green. Abnormal hydroxylated acylcarnitines are written in dark red. The presence and increase of hydroxylated forms of long-chain fatty acylcarnitines is evocative of LCHAD deficiency, and have prompted ex vivo fluxomic studies in order to explore more in-depth this diagnosis. B. Ex vivo fluxomic study of the mitochondrial β-oxidation on whole blood.De novo individual acylcarnitine synthesis from deuterated palmitate incubated with whole blood samples from our patient versus a healthy control is illustrated.

Fig. 2

Description of the two HADHA variants identified. A. Electropherograms of DNA sequencing. The c.1108G > A p.(Gly370Arg) variant is located in exon 12 and corresponds to a G to A nucleotide substitution. B. Cross-species protein conservation flanking p.(Gly370Arg).

Fig. 3

3D modeling of the p.(Gly370Arg) and p.(Glu510Gln) variants and impact on HADHA chain A conformation. The 3D structures of the novel variation p.(Gly370Arg) (A and B) and of the p.(Glu510Gln) (C and D) have been modelled with the swissmodel.expasy.org website (https://swissmodel.expasy.org) through upload of the FASTA sequences of wild and muted proteins. Panels A and B illustrate the occupancy at position 370 by glycine and arginine respectively (in purple). The replacement of a small uncharged residue (Gly370, A) by a bulky and charged one (Arg370, B) is expected to impact consequently protein structure and function. The extent of this impact might be partially attenuated but not cancelled by the displacement of the arginine at the periphery of the protein, thus minimizing steric hindrance with neighboring amino acid residues. The replacement of glutamate in position 510 (C) by glutamine (D), leads to the loss of hydrogen bonds (in dotted green lines) established between Glu510 and Thr547 or Tyr546. The location of this variant being internal, and not peripheral in contrast to p.(Gly370Arg), the loss of these hydrogen bonds should seriously impact protein stabilization and structure, and hence protein function.

Fig. 4

Schematic representation of HADHA gene and localization of protein domains and late-onset associated variants. Variations reported in late-onset LCHAD are located mostly in the linker domain encoded by exons 8 to 11. The novel p.(Gly370Arg) is located in close vicinity of this former domain, at the 5′ end of the exon 12 encoding the N-terminal end of the NAD binding domain. aa, amino acid; Nter, N-terminal.