Skeletal disease in a father and daughter with a novel monoallelic WNT1 mutation

A novel mutation in intron 1 of Wnt1 causes developmental loss of dopaminergic neurons in midbrain and ASD-like behaviors in rats

Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders with a strong genetic liability. Despite extensive studies, however, the underlying pathogenic mechanism still remains elusive. In the present study, we identified a homozygous mutation in the intron 1 of Wnt1 via large-scale screening of ASD risk/causative genes and verified that this mutation created a new splicing donor site in the intron 1, and consequently, a decrease of WNT1 expression. Interestingly, humanized rat models harboring this mutation exhibited robust ASD-like behaviors including impaired ultrasonic vocalization (USV), decreased social interactions, and restricted and repetitive behaviors. Moreover, in the substantia nigra compacta (SNpc) and the ventral tegmental area (VTA) of mutant rats, dopaminergic (DAergic) neurons were dramatically lost, together with a comparable decrease in striatal DAergic fibers. Furthermore, using single-cell RNA sequencing, we demonstrated that the decreased DAergic neurons in these midbrain areas might attribute to a shift of the boundary of the local pool of progenitor cells from the hypothalamic floor plate to the midbrain floor plate during the early embryonic stage. Moreover, treatments of mutant rats with levodopa could attenuate the impaired USV and social interactions almost completely, but not the restricted and repetitive behaviors. Our results for the first time documented that the developmental loss of DAergic neurons in the midbrain underlies the pathogenesis of ASD, and that the abnormal progenitor cell patterning is a cellular underpinning for this developmental DAergic neuronal loss. Importantly, the effective dopamine therapy suggests a translational significance in the treatment of ASD.

Case report: Early-onset osteoporosis in a patient carrying a novel heterozygous variant of the WNT1 gene

The WNT1 gene is crucial for bone development and homeostasis. Homozygous mutations in WNT1 cause severe bone fragility known as osteogenesis imperfecta type XV. Moreover, heterozygous WNT1 mutations have been found in adults with early-onset osteoporosis. We identified a 35 year-old Caucasian woman who experienced multiple vertebral fractures two months after her second pregnancy. There was no history of risk factors for secondary osteoporosis or family history of osteoporosis. Dual-energy X-ray absorptiometry confirmed a marked reduction of bone mineral density (BMD) at the lumbar spine (0.734 g/cm², Z-score -2.8), femoral neck (0.48 g/cm², Z-score -3.5), and total hip (0.589 g/cm², Z-score -3.0). Blood tests excluded secondary causes of bone fragility. Genetic analysis revealed a heterozygous missense mutation (p.Leu370Val) in the WNT1 gene. Varsome classified it as a variant of uncertain significance. However, the fact that the Leucine residue at position 370 is highly conserved among vertebrate species and the variant has a very low allelic frequency in the general population would exclude the possibility of a polymorphism. The patient was treated for two years with teriparatide therapy associated with calcium and vitamin D supplements. During the follow-up period she did not report further clinical fractures. After 24 months of teriparatide, BMD increased at lumbar spine (+14.6%), femoral neck (+8.3%) and total hip (+4.9%) compared to baseline. We confirm that the heterozygous WNT1 mutation could cause a variable bone fragility and low turnover osteoporosis. We suggest that teriparatide is one of the most appropriate available therapies for this case.

Analysis of the wnt1 regulatory chromosomal landscape

One of the earliest patterning events in the vertebrate neural plate is the specification of mes/r1, the territory comprising the prospective mesencephalon and the first hindbrain rhombomere. Within mes/r1, an interface of gene expression defines the midbrain-hindbrain boundary (MHB), a lineage restriction that separates the mesencephalon and rhombencephalon. wnt1 is critical to mes/r1 development and functions within the MHB as a component of the MHB gene regulatory network (GRN). Despite its importance to these critical and early steps of vertebrate neurogenesis, little is known about the factors responsible for wnt1 transcriptional regulation. In the zebrafish, wnt1 and its neighboring paralog, wnt10b, are expressed in largely overlapping patterns, suggesting co-regulation. To understand wnt1 and wnt10b transcriptional control, we used a comparative genomics approach to identify relevant enhancers. We show that the wnt1-wnt10b locus contains multiple cis-regulatory elements that likely interact to generate the wnt1 and wnt10b expression patterns. Two of 11 conserved enhancers tested show activity restricted to the midbrain and MHB, an activity that is conserved in the distantly related spotted gar orthologous elements. Three non-conserved elements also play a likely role in wnt1 regulation. The identified enhancers display dynamic modes of chromatin accessibility, suggesting controlled deployment during embryogenesis. Our results suggest that the control of wnt1 and wnt10b expression is under complex regulation involving the interaction of multiple enhancers.