Gaurav V. Harlalka

Defective mitochondrial mRNA maturation is associated with spastic ataxia.

In human mitochondria, polyadenylation of mRNA, undertaken by the nuclear-encoded mitochondrial poly(A) RNA polymerase, is essential for maintaining mitochondrial gene expression. Our molecular investigation of an autosomal-recessive spastic ataxia with optic atrophy, present among the Old Order Amish, identified a mutation of MTPAP associated with the disease phenotype. When subjected to poly(A) tail-length assays, mitochondrial mRNAs from affected individuals were shown to have severely truncated poly(A) tails. Although defective mitochondrial DNA maintenance underlies a well-described group of clinical disorders, our findings reveal a defect of mitochondrial mRNA maturation associated with human disease and imply that this disease mechanism should be considered in other complex neurodegenerative disorders.

Protective effect of Kalanchoe pinnata pers. (Crassulaceae) on gentamicin-induced nephrotoxicity in rats

Objective : The present study was undertaken to evaluate the aqueous extract of K. pinnata for its protective effects on gentamicin-induced nephrotoxicity in rats. Materials and Methods : Nephrotoxicity was induced in Wistar rats by intraperitoneal administration of gentamicin 100 mg/kg/day for eight days. Effect of concurrent administration of K. pinnata leaf extract at a dose of 125 mg/kg/day given by intraperitoneal route was determined using serum and urinary creatinine and blood urea nitrogen as indicators of kidney damage. The study groups contained six rats in each group. As nephrotoxicity of gentamicin is known to involve induction of oxidative stress, in vitro antioxidant activity and free radical-scavenging activity of this extract were evaluated. Result : It was observed that the aqueous extract of K. pinnata leaves significantly protects rat kidneys from gentamicin-induced histopathological changes. Gentamicin-induced glomerular congestion, peritubular and blood vessel congestion, epithelial desquamation, accumulation of inflammatory cells and necrosis of the kidney cells were found to be reduced in the group receiving the leaf extract of K. pinnata along with gentamicin. This extract also normalized the gentamicin-induced increases in urine and plasma creatinine, blood urea and blood urea nitrogen levels. In vitro studies revealed that the K. pinnata leaf extract possesses significant antioxidant as well as oxidative radical scavenging activities. Conclusion : It is proposed that the nephroprotective effect of the aqueous extract of K. pinnata leaves in gentamicin-induced nephrotoxicity may involve its antioxidant and oxidative radical scavenging activities.

Mutations in B4GALNT1 (GM2 synthase) underlie a new disorder of ganglioside biosynthesis

Glycosphingolipids are ubiquitous constituents of eukaryotic plasma membranes, and their sialylated derivatives, gangliosides, are the major class of glycoconjugates expressed by neurons. Deficiencies in their catabolic pathways give rise to a large and well-studied group of inherited disorders, the lysosomal storage diseases. Although many glycosphingolipid catabolic defects have been defined, only one proven inherited disease arising from a defect in ganglioside biosynthesis is known. This disease, because of defects in the first step of ganglioside biosynthesis (GM3 synthase), results in a severe epileptic disorder found at high frequency amongst the Old Order Amish. Here we investigated an unusual neurodegenerative phenotype, most commonly classified as a complex form of hereditary spastic paraplegia, present in families from Kuwait, Italy and the Old Order Amish. Our genetic studies identified mutations in B4GALNT1 (GM2 synthase), encoding the enzyme that catalyzes the second step in complex ganglioside biosynthesis, as the cause of this neurodegenerative phenotype. Biochemical profiling of glycosphingolipid biosynthesis confirmed a lack of GM2 in affected subjects in association with a predictable increase in levels of its precursor, GM3, a finding that will greatly facilitate diagnosis of this condition. With the description of two neurological human diseases involving defects in two sequentially acting enzymes in ganglioside biosynthesis, there is the real possibility that a previously unidentified family of ganglioside deficiency diseases exist. The study of patients and animal models of these disorders will pave the way for a greater understanding of the role gangliosides play in neuronal structure and function and provide insights into the development of effective treatment therapies.

Hypomorphic PCNA mutation underlies a human DNA repair disorder

Numerous human disorders, including Cockayne syndrome, UV-sensitive syndrome, xeroderma pigmentosum, and trichothiodystrophy, result from the mutation of genes encoding molecules important for nucleotide excision repair. Here, we describe a syndrome in which the cardinal clinical features include short stature, hearing loss, premature aging, telangiectasia, neurodegeneration, and photosensitivity, resulting from a homozygous missense (p.Ser228Ile) sequence alteration of the proliferating cell nuclear antigen (PCNA). PCNA is a highly conserved sliding clamp protein essential for DNA replication and repair. Due to this fundamental role, mutations in PCNA that profoundly impair protein function would be incompatible with life. Interestingly, while the p.Ser228Ile alteration appeared to have no effect on protein levels or DNA replication, patient cells exhibited marked abnormalities in response to UV irradiation, displaying substantial reductions in both UV survival and RNA synthesis recovery. The p.Ser228Ile change also profoundly altered PCNAs interaction with Flap endonuclease 1 and DNA Ligase 1, DNA metabolism enzymes. Together, our findings detail a mutation of PCNA in humans associated with a neurodegenerative phenotype, displaying clinical and molecular features common to other DNA repair disorders, which we showed to be attributable to a hypomorphic amino acid alteration.

Mutation of HERC2 causes developmental delay with Angelman-like features

Background Deregulation of the activity of the ubiquitin ligase E6AP (UBE3A) is well recognised to contribute to the development of Angelman syndrome (AS). The ubiquitin ligase HERC2, encoded by the HERC2 gene is thought to be a key regulator of E6AP. Methods and results Using a combination of autozygosity mapping and linkage analysis, we studied an autosomal-recessive neurodevelopmental disorder with some phenotypic similarities to AS, found among the Old Order Amish. Our molecular investigation identified a mutation in HERC2 associated with the disease phenotype. We establish that the encoded mutant HERC2 protein has a reduced half-life compared with its wild-type counterpart, which is associated with a significant reduction in HERC2 levels in affected individuals. Conclusions Our data implicate a model in which disruption of HERC2 function relates to a reduction in E6AP activity resulting in neurodevelopmental delay, suggesting a previously unrecognised role of HERC2 in the pathogenesis of AS.

PRUNE is crucial for normal brain development and mutated in microcephaly with neurodevelopmental impairment

Zollo et al. report that mutations in PRUNE1, a phosphoesterase superfamily molecule, underlie primary microcephaly and profound global developmental delay in four unrelated families from Oman, India, Iran and Italy. The study highlights a potential role for prune during microtubule polymerization, suggesting that prune syndrome may be a tubulinopathy.

Recessive nephrocerebellar syndrome on the Galloway-Mowat syndrome spectrum is caused by homozygous protein-truncating mutations of WDR73

Galloway-Mowat syndrome (GMS) is a neurodevelopmental disorder characterized by microcephaly, cerebellar hypoplasia, nephrosis, and profound intellectual disability. Jinks et al. extend the GMS spectrum by identifying a novel nephrocerebellar syndrome with selective striatal cholinergic interneuron loss and complete lateral geniculate nucleus delamination, caused by a frameshift mutation in WDR73.

Zinc disc implantation model of urinary bladder calculi and humane endpoints

The zinc disc implantation-induced urinary bladder calculi model in the rat is commonly used for preclinical evaluation of the antiurolithiatic activity of test compounds. Certain published reports state that relatively long durations for which zinc discs must be implanted in the bladders of rats. Hence, there is a need to refine this model. These investigations aimed to determine whether long-term studies using the zinc disc implantation model provide any additional data that affect the final outcomes of the study. In this study, we evaluated the effects of a well-known antiurolithiatic polyherbal drug, Cystone, for different treatment durations of 10, 20 and 48 days postimplantation. Our results indicate that even the shortest duration of 10 days is sufficient to reveal antiurolithiatic effects of a test drug. Hence, in the zinc disc implantation-induced urinary bladder calculi model, the study duration is proposed to be minimized so as to reduce the distress caused to the rats due to long-term exposure to the implant. Further, it is suggested that the growth of the bladder calculi can be monitored by taking X-ray radiographs of the bladder deposits to decide the time to terminate the study. Use of preformed calcium oxalate crystal instead of zinc discs, as suggested in earlier reports by others, may also be considered to avoid the sacrifice of rats at the end of the study.

A mutation of EPT1 (SELENOI) underlies a new disorder of Kennedy pathway phospholipid biosynthesis.

EPT1 encodes an enzyme involved in the Kennedy pathway of phospholipid biosynthesis, important for cell membrane integrity. Ahmed et al. identify an EPT1 mutation that impairs enzyme activity and causes complex motor neuron degenerative disease. This is the first human disorder shown to arise through Kennedy pathway dysfunction.

Novel Genetic, Clinical, and Pathomechanistic Insights into TFG‐Associated Hereditary Spastic Paraplegia

Hereditary spastic paraplegias (HSPs) are genetically and clinically heterogeneous axonopathies primarily affecting upper motor neurons and, in complex forms, additional neurons. Here, we report two families with distinct recessive mutations in TFG, previously suggested to cause HSP based on findings in a single small family with complex HSP. The first carried a homozygous c.317G>A (p.R106H) variant and presented with pure HSP. The second carried the same homozygous c.316C>T (p.R106C) variant previously reported and displayed a similarly complex phenotype including optic atrophy. Haplotyping and bisulfate sequencing revealed evidence for a c.316C>T founder allele, as well as for a c.316_317 mutation hotspot. Expression of mutant TFG proteins in cultured neurons revealed mitochondrial fragmentation, the extent of which correlated with clinical severity. Our findings confirm the causal nature of bi‐allelic TFG mutations for HSP, broaden the clinical and mutational spectra, and suggest mitochondrial impairment to represent a pathomechanistic link to other neurodegenerative conditions.