Movement disorders in valine métabolism diseases caused by HIBCH and ECHS1 deficiencies.

BACKGROUND AND PURPOSE: HIBCH and ECHS1 genes encode two enzymes implicated in the critical steps of valine catabolism, 3-hydroxyisobutyryl-coenzyme A (CoA) hydrolase (HIBCH) and short-chainenoyl-CoA hydratase (ECHS1), respectively. HIBCH deficiency (HIBCHD) and ECHS1 deficiency (ECHS1D) generate rare metabolic dysfunctions, often revealed by neurological symptoms. The aim of this study was to describe movement disorders spectrum in patients with pathogenic variants in ECHS1 and HIBC. METHODS: We reviewed a series of 18 patients (HIBCHD: 5; ECHS1D: 13) as well as 105 patients from the literature. We analysed the detailed phenotype of HIBCHD (38 patients) and ECHS1D (85 patients), focusing on MDs. RESULTS: The two diseases have a very similar neurological phenotype, with an early onset before 10 years of age for three clinical presentations: neonatal onset, Leigh-like syndrome (progressive onset or acute neurological decompensation), and isolated paroxysmal dyskinesia. Permanent or paroxysmal MDs were recorded in 61% of HIBCHD patients and 72% of ECHS1D patients. Patients had a variable combination of either isolated or combined MD, and dystonia was the main MD. These continuous MDs included dystonia, chorea, parkinsonism, athetosis, myoclonus, tremors, and abnormal eye movements. Patients with paroxysmal dyskinesia (HIBCHD: 4; ECHS1D: 9) usually had pure paroxysmal dystonia with normal clinical examination and no major impairment in psychomotor development. No correlation could be identified between clinical pattern (especially MD) and genetic pathogenic variants. CONCLUSIONS: Movement disorders, including abnormal ocular movements, are a hallmark of HIBCHD and ECHS1D. MDs are not uniform; dystonia is the most frequent, and various types of MD are combined in single patient.

Ablation of microRNA-155 and neuroinflammation in a mouse model of CLN1-disease.

Infantile neuronal ceroid lipofuscinosis (INCL), also known as CLN1-disease, is a devastating neurodegenerative lysosomal storage disorder (LSD), caused by inactivating mutations in the CLN1 gene. The Cln1-/- mice, which mimic INCL, manifest progressive neuroinflammation contributing to neurodegeneration. However, the underlying mechanism of neuroinflammation in INCL and in Cln1-/- mice has remained elusive. Previously, it has been reported that microRNA-155 (miR-155) regulates inflammation and miR profiling in Cln1-/- mouse brain showed that the level of miR-155 was upregulated. Thus, we sought to determine whether ablation of miR-155 in Cln1-/- mice may suppress neuroinflammation in these mice. Towards this goal, we generated Cln1-/-/miR-155-/- double-knockout mice and evaluated the inflammatory signatures in the brain. We found that the brains of double-KO mice manifest progressive neuroinflammatory changes virtually identical to those found in Cln1-/- mice. We conclude that ablation of miR-155 in Cln1-/- mice does not alter the neuroinflammatory trajectory in INCL mouse model.

CRISPR/Cas9-Mediated Knockout of GmFATB1 Significantly Reduced the Amount of Saturated Fatty Acids in Soybean Seeds.

Soybean (Glycine max) oil is one of the most widely used vegetable oils across the world. Breeding of soybean to reduce the saturated fatty acid (FA) content, which is linked to cardiovascular disease, would be of great significance for nutritional improvement. Acyl-acyl carrier protein thioesterases (FATs) can release free FAs and acyl-ACP, which ultimately affects the FA profile. In this study, we identified a pair of soybean FATB coding genes, GmFATB1a and GmFATB1b. Mutants that knock out either or both of the GmFATB1 genes were obtained via CRISPR/Cas9. Single mutants, fatb1a and fatb1b, showed a decrease in leaf palmitic and stearic acid contents, ranging from 11% to 21%. The double mutant, fatb1a:1b, had a 42% and 35% decrease in palmitic and stearic acid content, displayed growth defects, and were male sterility. Analysis of the seed oil profile revealed that fatb1a and fatb1b had significant lower palmitic and stearic acid contents, 39-53% and 17-37%, respectively, while that of the unsaturated FAs were the same. The relative content of the beneficial FA, linoleic acid, was increased by 1.3-3.6%. The oil profile changes in these mutants were confirmed for four generations. Overall, our data illustrate that GmFATB1 knockout mutants have great potential in improving the soybean oil quality for human health.

In a mouse model of INCL reduced S-palmitoylation of cytosolic thioesterase APT1 contributes to microglia proliferation and neuroinflammation.

S-palmitoylation is a reversible posttranslational modification in which a 16-carbon saturated fatty acid (generally palmitate) is attached to specific cysteine residues in polypeptides via thioester linkage. Dynamic S-palmitoylation (palmitoylation-depalmitoylation), like phosphorylation-dephosphorylation, regulates the function of numerous proteins, especially in the brain. While a family of 23 palmitoyl-acyl transferases (PATS), commonly known as ZDHHCs, catalyze S-palmitoylation of proteins, the thioesterases, localized either in the cytoplasm (eg, APT1) or in the lysosome (eg, PPT1) mediate depalmitoylation. Previously, we reported that APT1 requires dynamic S-palmitoylation for shuttling between the cytosol and the plasma membrane. APT1 depalmitoylated H-Ras to regulate its signaling pathway that stimulates cell proliferation. Although we demonstrated that APT1 catalyzed its own depalmitoylation, the ZDHHC(s) that S-palmitoylated APT1 had remained unidentified. We report here that ZDHHC5 and ZDHHC23 catalyze APT1 S-palmitoylation. Intriguingly, lysosomal Ppt1-deficiency in Cln1-/- mouse, a reliable animal model of INCL, markedly reduced ZDHHC5 and ZDHHC23 levels. Remarkably, in the brain of these mice decreased ZDHHC5 and ZDHHC23 levels suppressed membrane-bound APT1, thereby, increasing plasma membrane-localized H-Ras, which activated its signaling pathway stimulating microglia proliferation. Increased inflammatory cytokines produced by microglia together with increased complement C1q level contributed to the transformation of astrocytes to neurotoxic A1 phenotype. Importantly, neuroinflammation was ameliorated by treatment of Cln1-/- mice with a PPT1-mimetic small molecule, N-tert(Butyl)hydroxylamine (NtBuHA). Our results revealed a novel pathway to neuropathology in an INCL mouse model and uncovered a previously unrecognized mechanism of the neuroprotective actions of NtBuHA and its potential as a drug target.

Sirtuin 2 Regulates Protein LactoylLys Modifications.

Post-translational modifications (PTMs) play roles in both physiological and pathophysiological processes through the regulation of enzyme structure and function. We recently identified a novel PTM, lactoylLys, derived through a nonenzymatic mechanism from the glycolytic by-product, lactoylglutathione. Under physiologic scenarios, glyoxalase 2 prevents the accumulation of lactoylglutathione and thus lactoylLys modifications. What dictates the site-specificity and abundance of lactoylLys PTMs, however, remains unknown. Here, we report sirtuin 2 as a lactoylLys eraser. Using chemical biology and CRISPR-Cas9, we show that SIRT2 controls the abundance of this PTM both globally and on chromatin. These results address a major gap in our understanding of how nonenzymatic PTMs are regulated and controlled.

Paroxysmal Dyskinesias Revealing 3-Hydroxy-Isobutyryl-CoA Hydrolase (HIBCH) Deficiency.

Paroxysmal dyskinesias (PD) are rare movement disorders characterized by recurrent attacks of dystonia, chorea, athetosis, or their combination, with large phenotypic and genetic heterogeneity. 3-Hydroxy-isobutyryl-CoA hydrolase (HIBCH) deficiency is a neurodegenerative disease characterized in most patients by a continuous decline in psychomotor abilities or a secondary regression triggered by febrile infections and metabolic crises.We describe two PD patients from two pedigrees, both carrying a homozygous c.913A > G, p.Thr305Ala mutation in the HIBCH gene, associated with an unusual clinical presentation. The first patient presented in the second year of life with right paroxysmal hemidystonia lasting for 30 minutes, without any loss of consciousness and without any triggering factor. The second patient has presented since the age of 3 recurrent exercise-induced PD episodes which have been described as abnormal equinovarus, contractures of the lower limbs, lasting for 1 to 4 hours, associated with choreic movements of the hands. Their neurological examination and metabolic screening were normal, while brain magnetic resonance imaging showed abnormal signal of the pallidi.We suggest that HIBCH deficiency, through the accumulation of metabolic intermediates of the valine catabolic pathway, leads to a secondary defect in respiratory chain activity and pyruvate dehydrogenase (PDH) activity and to a broad phenotypic spectrum ranging from Leigh syndrome to milder phenotypes. The two patients presented herein expand the spectrum of the disease to include unusual paroxysmal phenotypes and HIBCH deficiency should be considered in the diagnostic strategy of PD to enable adequate preventive treatment.

Delineating the neurological phenotype in children with defects in the ECHS1 or HIBCH gene.

The neurological phenotype of 3-hydroxyisobutyryl-CoA hydrolase (HIBCH) and short-chain enoyl-CoA hydratase (SCEH) defects is expanding and natural history studies are necessary to improve clinical management. From 42 patients with Leigh syndrome studied by massive parallel sequencing, we identified five patients with SCEH and HIBCH deficiency. Fourteen additional patients were recruited through collaborations with other centres. In total, we analysed the neurological features and mutation spectrum in 19 new SCEH/HIBCH patients. For natural history studies and phenotype to genotype associations we also included 70 previously reported patients. The 19 newly identified cases presented with Leigh syndrome (SCEH, n = 11; HIBCH, n = 6) and paroxysmal dystonia (SCEH, n = 2). Basal ganglia lesions (18 patients) were associated with small cysts in the putamen/pallidum in half of the cases, a characteristic hallmark for diagnosis. Eighteen pathogenic variants were identified, 11 were novel. Among all 89 cases, we observed a longer survival in HIBCH compared to SCEH patients, and in HIBCH patients carrying homozygous mutations on the protein surface compared to those with variants inside/near the catalytic region. The SCEH p.(Ala173Val) change was associated with a milder form of paroxysmal dystonia triggered by increased energy demands. In a child harbouring SCEH p.(Ala173Val) and the novel p.(Leu123Phe) change, an 83.6% reduction of the protein was observed in fibroblasts. The SCEH and HIBCH defects in the catabolic valine pathway were a frequent cause of Leigh syndrome in our cohort. We identified phenotype and genotype associations that may help predict outcome and improve clinical management.

Spinal manifestations of CLN1 disease start during the early postnatal period.

AIM: To understand the progression of CLN1 disease and develop effective therapies we need to characterize early sites of pathology. Therefore, we performed a comprehensive evaluation of the nature and timing of early CLN1 disease pathology in the spinal cord, which appears especially vulnerable, and how this may affect behaviour. METHODS: We measured the spinal volume and neuronal number, and quantified glial activation, lymphocyte infiltration and oligodendrocyte maturation, as well as cytokine profile analysis during the early stages of pathology in Ppt1-deficient (Ppt1-/- ) mouse spinal cords. We then performed quantitative gait analysis and open-field behaviour tests to investigate the behavioural correlates during this period. RESULTS: We detected significant microglial activation in Ppt1-/- spinal cords at 1 month. This was followed by astrocytosis, selective interneuron loss, altered spinal volumes and oligodendrocyte maturation at 2 months, before significant storage material accumulation and lymphocyte infiltration at 3 months. The same time course was apparent for inflammatory cytokine expression that was altered as early as one month. There was a transient early period at 2 months when Ppt1-/- mice had a significantly altered gait that resembles the presentation in children with CLN1 disease. This occurred before an anticipated decline in overall locomotor performance across all ages. CONCLUSION: These data reveal disease onset 2 months (25% of life-span) earlier than expected, while spinal maturation is still ongoing. Our multi-disciplinary data provide new insights into the spatio-temporal staging of CLN1 pathogenesis during ongoing postnatal maturation, and highlight the need to deliver therapies during the presymptomatic period.

Comparative proteomic profiling reveals mechanisms for early spinal cord vulnerability in CLN1 disease.

CLN1 disease is a fatal inherited neurodegenerative lysosomal storage disease of early childhood, caused by mutations in the CLN1 gene, which encodes the enzyme Palmitoyl protein thioesterase-1 (PPT-1). We recently found significant spinal pathology in Ppt1-deficient (Ppt1-/-) mice and human CLN1 disease that contributes to clinical outcome and precedes the onset of brain pathology. Here, we quantified this spinal pathology at 3 and 7 months of age revealing significant and progressive glial activation and vulnerability of spinal interneurons. Tandem mass tagged proteomic analysis of the spinal cord of Ppt1-/-and control mice at these timepoints revealed a significant neuroimmune response and changes in mitochondrial function, cell-signalling pathways and developmental processes. Comparing proteomic changes in the spinal cord and cortex at 3 months revealed many similarly affected processes, except the inflammatory response. These proteomic and pathological data from this largely unexplored region of the CNS may help explain the limited success of previous brain-directed therapies. These data also fundamentally change our understanding of the progressive, site-specific nature of CLN1 disease pathogenesis, and highlight the importance of the neuroimmune response. This should greatly impact our approach to the timing and targeting of future therapeutic trials for this and similar disorders.

A phenotypically severe, biochemically "silent" case of HIBCH deficiency in a newborn diagnosed by rapid whole exome sequencing and enzymatic testing.

3-Hydroxyisobutyryl-CoA dehydrogenase (HIBCH) deficiency is a rare error in valine catabolism associated with a Leigh syndrome-like phenotype, mitochondrial dysfunction, and increased C4-OH. We report the most severe case to date in a full-term female who presented with poor feeding and nystagmus on day of life (DOL) 1. Although initial neuroimaging findings were concerning for metabolic disease, further metabolic testing was nondiagnostic and she was discharged on DOL 18. She was readmitted on DOL 22 after severe apneic episodes requiring intubation, with EEG demonstrating multifocal seizures and MRI/MRS demonstrating worsening findings. Care was withdrawn DOL 27 and she expired. Rapid whole exome sequencing (WES) demonstrated compound heterozygous variants in HIBCH with a paternal pathogenic variant (c.852delA, p.L284FfsX10) and a maternal likely pathogenic variant (c.488G>T, p.C163F). Fibroblast enzymatic testing demonstrated marked reduction in HIBCH levels. This case demonstrates the importance of rapid WES and follow-up functional testing in establishing a diagnosis when metabolic disease is suspected but lacks an expected biochemical signature.

Non-enzymatic Lysine Lactoylation of Glycolytic Enzymes.

Post-translational modifications (PTMs) regulate enzyme structure and function to expand the functional proteome. Many of these PTMs are derived from cellular metabolites and serve as feedback and feedforward mechanisms of regulation. We have identified a PTM that is derived from the glycolytic by-product, methylglyoxal. This reactive metabolite is rapidly conjugated to glutathione via glyoxalase 1, generating lactoylglutathione (LGSH). LGSH is hydrolyzed by glyoxalase 2 (GLO2), cycling glutathione and generating D-lactate. We have identified the non-enzymatic acyl transfer of the lactate moiety from LGSH to protein Lys residues, generating a "LactoylLys" modification on proteins. GLO2 knockout cells have elevated LGSH and a consequent marked increase in LactoylLys. Using an alkyne-tagged methylglyoxal analog, we show that these modifications are enriched on glycolytic enzymes and regulate glycolysis. Collectively, these data suggest a previously unexplored feedback mechanism that may serve to regulate glycolytic flux under hyperglycemic or Warburg-like conditions.

A therapeutic regimen for 3-hydroxyisobutyryl-CoA hydrolase deficiency with exercise-induced dystonia.

3-Hydroxyisobutyryl-CoA hydrolase (HIBCH) deficiency is a recently described disease resulting from mutations in HIBCH with no effective treatment. Here, we report a female Chinese patient presenting with exercise-induced dystonia and bilateral symmetrical hyperintensities of the globus pallidus on brain MRI associated with novel HIBCH mutations (c.1027C>G;p. H343D and c.383T>A;p.V128D). After treatment for 1 year with a low-valine diet, both clinical symptoms and brain lesions improved substantially. We propose that HIBCH deficiency should be considered in the differential diagnosis for patients with exercise-induced dystonia, particularly if bilateral symmetrical lesions in the globus pallidus are present. A low-valine diet is a potentially promising treatment for HIBCH deficiency.

Mice deficient in the lysosomal enzyme palmitoyl-protein thioesterase 1 (PPT1) display a complex retinal phenotype.

Neuronal ceroid lipofuscinosis (NCL) type 1 (CLN1) is a neurodegenerative storage disorder caused by mutations in the gene encoding the lysosomal enzyme palmitoyl-protein thioesterase 1 (PPT1). CLN1 patients suffer from brain atrophy, mental and motor retardation, seizures, and retinal degeneration ultimately resulting in blindness. Here, we performed an in-depth analysis of the retinal phenotype of a PPT1-deficient mouse, an animal model of this condition. Reactive astrogliosis and microgliosis were evident in mutant retinas prior to the onset of retinal cell loss. Progressive accumulation of storage material, a pronounced dysregulation of various lysosomal proteins, and accumulation of sequestosome/p62-positive aggregates in the inner nuclear layer also preceded retinal degeneration. At advanced stages of the disease, the mutant retina was characterized by a significant loss of ganglion cells, rod and cone photoreceptor cells, and rod and cone bipolar cells. Results demonstrate that PPT1 dysfunction results in early-onset pathological alterations in the mutant retina, followed by a progressive degeneration of various retinal cell types at relatively late stages of the disease. Data will serve as a reference for future work aimed at developing therapeutic strategies for the treatment of retinal degeneration in CLN1 disease.

Targeting HIBCH to reprogram valine metabolism for the treatment of colorectal cancer.

Valine catabolism is known to be essential for cancer cells but the detailed mechanism remains unclear. This study is to explore the critical roles of 3-hydroxyisobutyryl-CoA hydrolase (HIBCH) in colorectal cancers (CRC) and to develop a new therapy returning valine metabolism homeostasis. High HIBCH expression was first confirmed to correlate with poor survival in patients with CRC, which was then linked to the increased cell growth, resistant apoptosis, and decreased autophagy in CRC cells. The functions of HIBCH in CRC were dependent on its mitochondrial localization. High HIBCH level was further demonstrated to promote the metabolism of tricarboxylic acid cycle as well as oxidative phosphorylation in CRC cells. Based on above findings, we further discovered a novel valine catabolism inhibitor SBF-1. The pharmacological blockade of HIBCH mitochondrial localization with SBF-1 resulted in decreased cancer cell growth and increased autophagy, collectively contributing to the antitumor effect both in vitro and in vivo. Moreover, anti-VEGF therapy with bevacizumab increased HIBCH level in CRC cells, which in turn caused the resistance to the therapy. The interference with HIBCH function by SBF-1 significantly increased the antitumor efficacy of bevacizumab and led to a robust survival benefit. The present study identified HIBCH as a critical enzyme of valine catabolism in CRC progression and resistance to anti-VEGF therapy. We also provided a novel HIBCH inhibitor SBF-1, which highlighted the combined therapy using valine catabolic inhibitor along with anti-VEGF drugs, to control progression of CRC.

Developmental NMDA receptor dysregulation in the infantile neuronal ceroid lipofuscinosis mouse model.

Protein palmitoylation and depalmitoylation alter protein function. This post-translational modification is critical for synaptic transmission and plasticity. Mutation of the depalmitoylating enzyme palmitoyl-protein thioesterase 1 (PPT1) causes infantile neuronal ceroid lipofuscinosis (CLN1), a pediatric neurodegenerative disease. However, the role of protein depalmitoylation in synaptic maturation is unknown. Therefore, we studied synapse development in Ppt1-/- mouse visual cortex. We demonstrate that the developmental N-methyl-D-aspartate receptor (NMDAR) subunit switch from GluN2B to GluN2A is stagnated in Ppt1-/- mice. Correspondingly, Ppt1-/- neurons exhibit immature evoked NMDAR currents and dendritic spine morphology in vivo. Further, dissociated Ppt1-/- cultured neurons show extrasynaptic, diffuse calcium influxes and enhanced vulnerability to NMDA-induced excitotoxicity, reflecting the predominance of GluN2B-containing receptors. Remarkably, Ppt1-/- neurons demonstrate hyperpalmitoylation of GluN2B as well as Fyn kinase, which regulates surface retention of GluN2B. Thus, PPT1 plays a critical role in postsynapse maturation by facilitating the GluN2 subunit switch and proteostasis of palmitoylated proteins.

Lysophospholipases cooperate to mediate lipid homeostasis and lysophospholipid signaling.

Lysophospholipids (LysoPLs) are bioactive lipid species involved in cellular signaling processes and the regulation of cell membrane structure. LysoPLs are metabolized through the action of lysophospholipases, including lysophospholipase A1 (LYPLA1) and lysophospholipase A2 (LYPLA2). A new X-ray crystal structure of LYPLA2 compared with a previously published structure of LYPLA1 demonstrated near-identical folding of the two enzymes; however, LYPLA1 and LYPLA2 have displayed distinct substrate specificities in recombinant enzyme assays. To determine how these in vitro substrate preferences translate into a relevant cellular setting and better understand the enzymes' role in LysoPL metabolism, CRISPR-Cas9 technology was utilized to generate stable KOs of Lypla1 and/or Lypla2 in Neuro2a cells. Using these cellular models in combination with a targeted lipidomics approach, LysoPL levels were quantified and compared between cell lines to determine the effect of losing lysophospholipase activity on lipid metabolism. This work suggests that LYPLA1 and LYPLA2 are each able to account for the loss of the other to maintain lipid homeostasis in cells; however, when both are deleted, LysoPL levels are dramatically increased, causing phenotypic and morphological changes to the cells.

Compromised astrocyte function and survival negatively impact neurons in infantile neuronal ceroid lipofuscinosis.

The neuronal ceroid lipofuscinoses (NCLs) are the most common cause of childhood dementia and are invariably fatal. Early localized glial activation occurs in these disorders, and accurately predicts where neuronal loss is most pronounced. Recent evidence suggests that glial dysfunction may contribute to neuron loss, and we have now explored this possibility in infantile NCL (INCL, CLN1 disease). We grew primary cultures of astrocytes, microglia, and neurons derived from Ppt1 deficient mice (Ppt1-/-) and assessed their properties compared to wildtype (WT) cultures, before co-culturing them in different combinations (astrocytes with microglia, astrocytes or microglia with neurons, all three cell types together). These studies revealed that both Ppt1-/- astrocytes and microglia exhibit a more activated phenotype under basal unstimulated conditions, as well as alterations to their protein expression profile following pharmacological stimulation. Ppt1- /- astrocytes also displayed abnormal calcium signalling and an elevated cytoplasmic Ca2+ level, and a profound defect in their survival. Ppt1-/- neurons displayed decreased neurite outgrowth, altered complexity, a reduction in cell body size, and impaired neuron survival with prolonged time in culture. In co-cultures, the presence of both astrocytes and microglia from Ppt1-/- mice further impaired the morphology of both wild type and Ppt1-/- neurons. This negative influence was more pronounced for Ppt1-/- microglia, which appeared to trigger increased Ppt1-/- neuronal death. In contrast, wild type glial cells, especially astrocytes, ameliorated some of the morphological defects observed in Ppt1-/- neurons. These findings suggest that both Ppt1-/- microglia and astrocytes are dysfunctional and may contribute to the neurodegeneration observed in CLN1 disease. However, the dysfunctional phenotypes of Ppt1-/- glia are different from those present in CLN3 disease, suggesting that the pathogenic role of glia may differ between NCLs.

[Diagnosis and treatment of 3-hydroxyisobutyryl-CoA hydrolase deficiency: a case report and literature review].

A case of 3-hydroxyisobutyryl-CoA hydrolase deficiency was reported, and its clinical features, gene mutation characteristics, and diagnosis and treatment were analyzed with reference to related literature. The patient aged 1 year and 6 months had developmental regression and paroxysmal dystonia after pyrexia and diarrhea, and head MRI showed symmetrical lesions in the bilateral basal ganglia. No pathogenic mutation was found in the full-length detection of mitochondrial genome. Nuclear gene detection of mitochondrial-related diseases found new compound heterozygous mutations in the HIBCH gene, i.e., c.439-2A>G and c.958A>G (p.K320E), which were inherited from his father and mother, respectively. The boy was given cocktail therapy, dietary valine restriction, and symptomatic treatment. After 2 weeks of treatment, there were improvements in dystonia and motor and intellectual development.

Truncating mutations of HIBCH tend to cause severe phenotypes in cases with HIBCH deficiency: a case report and brief literature review.

3-hydroxyisobutryl-CoA hydrolase (HIBCH) deficiency is a rare inborn error of valine metabolism characterized by neurodegenerative symptoms and caused by recessive mutations in the HIBCH gene. In this study, utilizing whole exome sequencing, we identified two novel splicing mutations of HIBCH (c.304+3A>G; c.1010_1011+3delTGGTA) in a Chinese patient with characterized neurodegenerative features of HIBCH deficiency and bilateral syndactyly which was not reported in previous studies. Functional tests showed that both of these two mutations destroyed the normal splicing and reduced the expression of HIBCH protein. Through a literature review, a potential phenotype-genotype correlation was found that patients carrying truncating mutations tended to have more severe phenotypes compared with those with missense mutations. Our findings would widen the mutation spectrum of HIBCH causing HIBCH deficiency and the phenotypic spectrum of the disease. The potential genotype-phenotype correlation would be profitable for the treatment and management of patients with HIBCH deficiency.