Multidimensional analysis and therapeutic development using patient iPSC-derived disease models of Wolfram syndrome

Wolfram syndrome is a rare genetic disorder largely caused by pathogenic variants in the WFS1 gene and manifested by diabetes mellitus, optic nerve atrophy, and progressive neurodegeneration. Recent genetic and clinical findings have revealed Wolfram syndrome as a spectrum disorder. Therefore, a genotype-phenotype correlation analysis is needed for diagnosis and therapeutic development. Here, we focus on the WFS1 c.1672C>T, p.R558C variant, which is highly prevalent in the Ashkenazi Jewish population. Clinical investigation indicated that patients carrying the homozygous WFS1 c.1672C>T, p.R558C variant showed mild forms of Wolfram syndrome phenotypes. Expression of WFS1 p.R558C was more stable compared with the other known recessive pathogenic variants associated with Wolfram syndrome. Human induced pluripotent stem cell-derived (iPSC-derived) islets (SC-islets) homozygous for WFS1 c.1672C>T variant recapitulated genotype-related Wolfram syndrome phenotypes. Enhancing residual WFS1 function through a combination treatment of chemical chaperones mitigated detrimental effects caused by the WFS1 c.1672C>T, p.R558C variant and increased insulin secretion in SC-islets. Thus, the WFS1 c.1672C>T, p.R558C variant causes a mild form of Wolfram syndrome phenotypes, which can be remitted with a combination treatment of chemical chaperones. We demonstrate that our patient iPSC-derived disease model provides a valuable platform for further genotype-phenotype analysis and therapeutic development for Wolfram syndrome.

Further Delineation of the Clinical and Pathologic Features of HIKESHI-Related Hypomyelinating Leukodystrophy

BACKGROUND

A recurrent homozygous missense variant, c.160G>C;p.(Val54Leu) in HIKESHI, was found to cause a hypomyelinating leukodystrophy with high frequency in the Ashkenazi Jewish population. We provide extended phenotypic classification of this disorder based on clinical history of a further seven affected individuals, assess carrier frequency in the Ashkenazi Jewish population, and provide a neuropathological study.

METHODS

Clinical information, neuroimaging, and biosamples were collected. Brain autopsy was performed for one case.

RESULTS

Individuals with HIKESHI-related disease share common clinical features: early axial hypotonia evolving to dystonia or with progressive spasticity, hyperreflexia and clonus, feeding difficulties with poor growth, and nystagmus. Severe morbidity or death during febrile illness occurred in five of the nine affected individuals. Magnetic resonance images of seven patients were analyzed and demonstrated diffuse hypomyelination and thin corpus callosum. Genotyping data of more than 125,000 Ashkenazi Jewish individuals revealed a carrier frequency of 1 in 216. Gross pathology examination in one case revealed abnormal white matter. Microscopically, there was a near-total absence of myelin with a relative preservation of axons. The cerebral white matter showed several reactive astrocytes and microglia.

CONCLUSIONS

We provide pathologic evidence for a primary disorder of the myelin in HIKESHI-related leukodystrophy. These findings are consistent with the hypomyelination seen in brain magnetic resonance imaging and with the clinical features of early-onset spastic/dystonic quadriplegia and nystagmus. The high carrier rate of the recurrent variant seen in the Ashkenazi Jewish population requires increased attention to screening and diagnosis of this condition, particularly in this population.

Severe epileptic encephalopathy associated with compound heterozygosity of THG1L variants in the Ashkenazi Jewish population

THG1L-associated autosomal recessive ataxia belongs to a group of disorders that occur due to abnormal mitochondrial tRNA modification. The product of THG1L is the tRNA-histidine guanylyltransferase 1-like enzyme that catalyzes the 3'-5"addition of guanine to the 5"-end of tRNA-histidine in the mitochondrion. To date, five individuals with homozygosity for p.(Val55Ala) in THG1L have been reported and presented with mild delays or normal development and cerebellar dysfunction. We present seven individuals with biallelic variants in THG1L. Three individuals were compound heterozygous for the p.(Cys51Trp) and p.(Val55Ala) variants and presented with profound developmental delays, microcephaly, intractable epilepsy, and cerebellar hypoplasia. Four siblings were homozygous for the p.(Val55Ala) variant and presented with cerebellar ataxia with cerebellar vermis hypoplasia, dysarthria, mild developmental delays, and normal/near-normal cognition. All seven patients were of Ashkenazi Jewish descent. Carrier rates for the two variants were calculated in a cohort of 26,731 Ashkenazi Jewish individuals tested by the Dor Yeshorim screening program. The p.(Cys51Trp) variant is novel and was found in 40 of the Ashkenazi Jewish individuals tested, with a carrier rate of 1 in 668 (0.15%). The p.(Val55Ala) variant was found in 229 of the Ashkenazi Jewish individuals tested, with a carrier rate of 1 in 117 (0.85%). The individuals with compound heterozygosity of the p.(Val55Ala) and p.(Cys51Trp) variants expand the phenotypic spectrum of THG1L-related disorders to include severe epileptic encephalopathy. The individuals with homozygosity of the p.(V55A) variant further establish the associated mild and slowly progressive or nonprogressive neurodevelopmental phenotype.

Novel Y-Chromosome Long Non-Coding RNAs Expressed in Human Male CNS During Early Development

Global microarray gene expression analyses previously demonstrated differences in female and male embryos during neurodevelopment. In particular, before sexual maturation of the gonads, the differences seem to concentrate on the expression of genes encoded on the X- and Y-chromosomes. To investigate genome-wide differences in expression during this early developmental window, we combined high-resolution RNA sequencing with qPCR to analyze brain samples from human embryos during the first trimester of development. Our analysis was tailored for maximum sensitivity to discover Y-chromosome gene expression, but at the same time, it was underpowered to detect X-inactivation escapees. Using this approach, we found that 5 out of 13 expressed gametolog pairs showed unbalanced gene dosage, and as a consequence, a male-biased expression. In addition, we found six novel non-annotated long non-coding RNAs on the Y-chromosome with conserved expression patterns in newborn chimpanzee. The tissue specific and time-restricted expression of these long non-coding RNAs strongly suggests important functions during central nervous system development in human males.

Spatial sexual dimorphism of X and Y homolog gene expression in the human central nervous system during early male development

BACKGROUND

Renewed attention has been directed to the functions of the Y chromosome in the central nervous system during early human male development, due to the recent proposed involvement in neurodevelopmental diseases. PCDH11Y and NLGN4Y are of special interest because they belong to gene families involved in cell fate determination and formation of dendrites and axon.

METHODS

We used RNA sequencing, immunocytochemistry and a padlock probing and rolling circle amplification strategy, to distinguish the expression of X and Y homologs in situ in the human brain for the first time. To minimize influence of androgens on the sex differences in the brain, we focused our investigation to human embryos at 8-11 weeks post-gestation.

RESULTS

We found that the X- and Y-encoded genes are expressed in specific and heterogeneous cellular sub-populations of both glial and neuronal origins. More importantly, we found differential distribution patterns of X and Y homologs in the male developing central nervous system.

CONCLUSIONS

This study has visualized the spatial distribution of PCDH11X/Y and NLGN4X/Y in human developing nervous tissue. The observed spatial distribution patterns suggest the existence of an additional layer of complexity in the development of the male CNS.

Microarray Analysis of Copy Number Variants on the Human Y Chromosome Reveals Novel and Frequent Duplications Overrepresented in Specific Haplogroups

BACKGROUND

The human Y chromosome is almost always excluded from genome-wide investigations of copy number variants (CNVs) due to its highly repetitive structure. This chromosome should not be forgotten, not only for its well-known relevance in male fertility, but also for its involvement in clinical phenotypes such as cancers, heart failure and sex specific effects on brain and behaviour.

RESULTS

We analysed Y chromosome data from Affymetrix 6.0 SNP arrays and found that the signal intensities for most of 8179 SNP/CN probes in the male specific region (MSY) discriminated between a male, background signals in a female and an isodicentric male containing a large deletion of the q-arm and a duplication of the p-arm of the Y chromosome. Therefore, this SNP/CN platform is suitable for identification of gain and loss of Y chromosome sequences. In a set of 1718 males, we found 25 different CNV patterns, many of which are novel. We confirmed some of these variants by PCR or qPCR. The total frequency of individuals with CNVs was 14.7%, including 9.5% with duplications, 4.5% with deletions and 0.7% exhibiting both. Hence, a novel observation is that the frequency of duplications was more than twice the frequency of deletions. Another striking result was that 10 of the 25 detected variants were significantly overrepresented in one or more haplogroups, demonstrating the importance to control for haplogroups in genome-wide investigations to avoid stratification. NO-M214(xM175) individuals presented the highest percentage (95%) of CNVs. If they were not counted, 12.4% of the rest included CNVs, and the difference between duplications (8.9%) and deletions (2.8%) was even larger.

CONCLUSIONS

Our results demonstrate that currently available genome-wide SNP platforms can be used to identify duplications and deletions in the human Y chromosome. Future association studies of the full spectrum of Y chromosome variants will demonstrate the potential involvement of gain or loss of Y chromosome sequence in different human phenotypes.