BVVL/ FL: features caused by SLC52A3 mutations; WDFY4 and TNFSF13B may be novel causative genes

Atypical presentations in an RTD patient and report of novel SLC52A3 and SLC52A2 mutations

INTRODUCTION

Riboflavin Transporter Deficiency (RTD) is a rare neurological disorder characterized by pontobulbar palsy, hearing loss, and motor cranial nerve involvement. SLC52A3 and SLC52A2 mutations are causes of RTD. SLC52A2 mutations are usually found in childhood onset cases. Fifteen Iranian RTD diagnosed patients without SLC52A2 mutations have been previously described. We aimed to identify causative mutations in two childhood cases.

METHODS

We recruited patients with diagnosis of BVVL. Comprehensive clinical evaluations were performed on the patients. SLC52A3 and SLC52A2 genes were PCR-amplified and Sanger sequenced. Candidate disease causing variations were screened for segregation with disease status in the respective families and control individuals.

RESULTS

A novel homozygous SLC52A3 mutation (p.Met1Val) and a heterozygous SLC52A2 mutation (p.Ala288Val) were both observed in one proband with typical RTD presentations. The aggregate of presentations in the early stages of disease in the second patient that included weakness in the lower extremities, absence of bulbar or hearing defects, prominent sensory polyneuropathy as evidenced in electrodiagnostic studies, and absence of sensory symptoms including sensory ataxia did not prompt immediate RTD diagnosis. Dysarthria and decreased hearing manifested later in the disease course. A novel homozygous SLC52A2 (p.Val314Met) mutation was identified.

CONCLUSION

A literature search found recent reports of other atypical RTD presentations. These include MRI findings, speech understanding difficulties accompanied by normal hearing, anemia, and left ventricular non-compaction. Knowledge of unusual presentations lessens the chance of misdiagnosis or delayed RTD diagnosis which, in light of favorable effects of riboflavin supplementation, is of immense importance.

Comparative analysis of the nucleus accumbens transcriptional features in multiple depressive animal models

Chronic stress is deemed a significant clinical contributor to depression. The use of animal models of chronic stress can fully reveal the complex pathological mechanisms and their changing trends in the pathogenesis of depression, which is crucial for both disease prevention and therapy. It is also unknown how various forms of stress differ in their impact on animal physiology and behavior. The nucleus accumbens (NAc), an essential brain area for the pathophysiology of depression, and its underlying neural mechanisms remain unclear. Here, we systematically compared transcriptional signatures in the NAc of four chronic stress models in rats: chronic unpredictable mild stress (CUMS), chronic social defeat stress (CSDS), learned helplessness (LH), chronic restraint stress (CRS). The majority of differentially expressed genes (DEGs) were unique to a single depression model, while the rank-rank hypergeometric overlap analysis showed that the CSDS and CRS models had the greatest overlap, and the CRS and CUMS models had the least. Then, we performed pathway analysis of the differential genes and found that the neuroactive ligand-receptor interaction pathway was significantly enriched not only in the LH, CRS and CSDS stress models, but also significantly enriched in stress genes that were also altered in at least two stress models. Finally, we found three hub genes (Dcx, Tnc and Wdfy4) by constructing co-expression networks for stress genes. In summary, our research has the potential to offer fresh insights into the molecular mechanisms underlying depression induced by different types of stress, highlighting both their similarities and differences. It may provide valuable clues for understanding the pathogenesis of depression.

Identification of a mutation in TNRC18 in a patient with clinical features of Fazio-Londe disease

Fazio-Londe disease and Brown-Vialetto-Van Laere syndrome are rare related neurological disorders. Although SLC52A3 and SLC52A2 that encode riboflavin transporters are their only known causative genes, many patients without mutations in these genes have been reported. Clinical and genetic data of a patient with features suggestive of Fazio-Londe disease are presented. Neurological examination revealed significant involvement of cranial nerves and weakness in the lower extremities. Pontobulbar presentations were prominent. EDX study suggested motor neuronopathy. Hearing was normal. She was diagnosed with FL disease. Response to riboflavin supplementation was not favorable. The patient's pedigree suggested recessive inheritance. SLC52A3 and SLC52A2 were screened and mutations were not observed. Results of exome sequencing and segregation analysis suggested that a mutation in TNRC18 is a candidate cause of disease in the patient. The three dimensional structure of the TNRC18 protein was predicted and it was noted that its two conserved domains (BAH and Tudor) interact and that the valine residue affected by the mutation is positioned close to both domains. A mutation in TNRC18 is cautiously reported as the possible cause of FL disease in the patient. The finding warrants further inquiries on TNRC18 about which little is presently known.

Benefit of high-dose oral riboflavin therapy in riboflavin transporter deficiency

Riboflavin transporter deficiency (RTD) is a progressive inherited neuropathy of childhood onset, characterised by pontobulbar palsy, sensorineural deafness, sensory ataxia, muscle weakness, optic atrophy and respiratory failure. Riboflavin supplementation is beneficial in short-term reports, but the quantum of benefit in various clinical domains is not well understood. A PubMed search was conducted, which identified 94 genetically confirmed cases of RTD who received riboflavin supplementation and had follow-up assessments. Information on the clinical and functional status before and after riboflavin supplementation was collected and analysed. Seventy-six of the 94 patients (80.9%) showed an overall improvement after riboflavin supplementation, and the remaining (19.1%) were stable, though some patients had deteriorations in individual domains with no reported deaths. The domains that had the highest rates of response to riboflavin supplementation were gross motor function (93.3% improved), bulbar palsy (91.3%) and ataxia (90.0%). Improvements were also seen in limb muscle weakness, audiology, facial nerve palsy and respiratory function. Despite treatment, many patients required assistance to ambulate and had severe or profound hearing loss and some remained gastrostomy or tracheostomy dependent. Riboflavin supplementation is a lifesaving intervention for patients with RTD and results in a profound improvement in several functional domains, with early diagnosis and treatment further improving outcomes. Despite treatment, patients are left with residual disability. There is a need to accurately measure functional outcomes in children with RTD and develop additional disease-modifying therapies.