Potential Role of Brain-Derived Neurotrophic Factor and Dopamine Receptor D2 Gene Variants as Modifiers for the Susceptibility and Clinical Course of Wilson's Disease

An Effort to Identify Genetic Determinants in Siblings With Wilson Disease Manifesting Striking Clinical Heterogeneity: An Exome Profiling Study of Two Indian Families

BACKGROUND

Wilson disease (WD) is a rare autosomal recessive disorder of copper metabolism caused due to mutations in the copper transporter ATP7B. There is often a striking variability of clinical manifestations among patients with ATP7B mutations, including in siblings. This phenomenon may be caused by individual differences in copper accumulation in hepatocytes and intolerance to copper toxicity as governed by genetic variations in copper metabolism genes acting as modifier loci to the disease.

OBJECTIVE

To elucidate the genetic basis of striking clinical heterogeneity among two siblings of two families with WD.

METHODS

The disease diagnosis and subsequent clinical examinations were performed by expert clinicians. The younger siblings in both families presented with early neurological manifestations at a younger age than their older siblings. Interestingly, only the younger siblings were reported to have had hepatic manifestations. Exome sequencing of all the four individuals was performed to understand their heterogeneous phenotypic outcomes.

RESULTS

Genetic screening revealed no difference in the ATP7B variant spectrum between the siblings of each family. However, the siblings of both the families were found to harbor mutually exclusive pathogenic variants in suspected modifier genes implicated in copper metabolism and/or other neurological and hepatic disorders having overlapping symptoms with WD, viz., CFTR, PPARG, ABCB11, ATP7A, CYP2D6, mTOR, TOR1A, and CP, which can potentially explain their differential clinical phenotypes.

CONCLUSION

Clinical heterogeneity between siblings with WD with the same ATP7B mutation profile may be attributed to the presence of different pathogenic variants in potential modifier genes.

HDACi protects against vascular cognitive impairment from CCH injury via induction of BDNF-related AMPA receptor activation

We previously showed a hydroxamic acid‐based histone deacetylase inhibitor (HDACi), compound 13, provides neuroprotection against chronic cerebral hypoperfusion (CCH) both in vitro under oxygen‐glucose deprivation (OGD) conditions and in vivo under bilateral common carotid artery occlusion (BCCAO) conditions. Intriguingly, the protective effect of this HDACi is via H3K14 or H4K5 acetylation–mediated differential BDNF isoform activation. BDNF is involved in cell proliferation and differentiation in development, synaptic plasticity and in learning and memory related with receptors or synaptic proteins. B6 mice underwent BCCAO and were randomized into 4 groups; a sham without BCCAO (sham), BCCAO mice injected with DMSO (DMSO), mice injected with HDACi‐compound 13 (compound 13) and mice injected with suberoylanilide hydroxamic acid (SAHA). The cortex and hippocampus of mice were harvested at 3 months after BCCAO, and levels of BDNF, AMPA receptor and dopamine receptors (D1, D2 and D3) were studied using Western blotting analysis or immunohistochemistry. We found that the AMPA receptor plays a key role in the molecular mechanism of this process by modulating HDAC. This protective effect of HDACi may be through BDNF; therefore, activation of this downstream signalling molecule, for example by AMPA receptors, could be a therapeutic target or intervention applied under CCH conditions.

Dopamine β hydroxylase (DBH) polymorphisms do not contribute towards the clinical course of Wilson's disease in Indian patients

BACKGROUND

Wilson's disease (WD) is a rare copper metabolism disorder with hepatic and neurological symptoms. Dopamine β hydroxylase (DBH) encodes a copper-dependent mono-oxygenase that converts dopamine to norepinephrine, thereby regulating the endogenous dopamine content in the neurons. Polymorphisms of DBH have been reported to be associated with several neurological diseases, such as Parkinson's disease, Alzheimer's disease, schizophrenia and attention-deficit hyperactivity disorder, which have overlapping neurological symptoms with WD. The present study aimed to assess the role of DBH polymorphisms on the clinical course of WD.

METHODS

In total, 141 WD patients from India were included in the present study. Three polymorphisms of DBH (rs1611115 in the promoter, rs1108580 in exon 2 and rs129882 in 3'-UTR) were screened for their association with the clinical attributes (hepatic and neurological features) and age of onset of WD using a polymerase chain reaction-restriction fragment length polymorphsm method and sequencing approach. The distribution of genotype or allele frequencies was tested using 2 × 2 contingency chi-squared and logistic regression analysis (additive, dominant and recessive model).

RESULTS

The genotypic and allelic frequencies of these single nucleotide polymophisms did not vary significantly along with the clinical symptoms (hepatic and neurological) or the age of onset of WD. No significant association was observed when we analyzed our samples with respect to harboring different kinds of ATP7B mutations (nonsense/in-del and missense).

CONCLUSIONS

The data obtained in the present study suggest that the selected DBH variants are unlikely to have any significant contribution towards modifying the clinical symptoms of Indian WD patients.