The T-locus - inspiration and distraction?

The T/t locus was a major focus of study by mouse geneticists during the 20th century. In the 70s, as the study of cell surface antigens controlling transplantation antigens was taking off, several laboratories hypothesized that alleles of this locus would control cell surface antigens important for embryonic development. One such antigen, the embryonal carcinoma F9 antigen was said to be an example. Other antigens were described on sperm and embryos that were said to be controlled by alleles at the T/t complex. These findings were later found to be false. The history of the findings and their refutation is described.

Acute cholangitis following mRNA COVID-19 vaccine booster in a patient receiving an anti-amyloid antibody for Alzheimer's disease: A case report.

A 77-year-old woman had 2 weeks of fever and flu-like symptoms starting several hours after receiving an mRNA booster for SARS-CoV-2 and the influenza vaccine, in separate shots. Laboratory tests showed cholangitis. Medical history included APOE-ε4 carrier genotype, mild Alzheimer's disease, participation in a clinical trial of aducanumab, and resolving polymyalgia rheumatica. The patient recovered with at-home supportive care. She had aducanumab-associated amyloid-related imaging abnormalities-edema (ARIA-E) both before and after the acute cholangitis. Two months following the vaccinations polymyalgia rheumatica recurred. This case raises questions about interactions among immune-mediated disease, complications of anti-amyloid monoclonal antibodies, and adverse events following SARS-CoV-2 mRNA vaccination.

The Cerebellum in Niemann-Pick C1 Disease: Mouse Versus Man.

Selective neuronal vulnerability is common to most degenerative disorders, including Niemann-Pick C (NPC), a rare genetic disease with altered intracellular trafficking of cholesterol. Purkinje cell dysfunction and loss are responsible for cerebellar ataxia, which is among the prevailing neurological signs of the NPC disease. In this review, we focus on some questions that are still unresolved. First, we frame the cerebellar vulnerability in the context of the extended postnatal time length by which the development of this structure is completed in mammals. In line with this thought, the much later development of cerebellar symptoms in humans is due to the later development and/or maturation of the cerebellum. Hence, the occurrence of developmental events under a protracted condition of defective intracellular cholesterol mobilization hits the functional maturation of the various cell types generating the ground of increased vulnerability. This is particularly consistent with the high cholesterol demand required for cell proliferation, migration, differentiation, and synapse formation/remodeling. Other major questions we address are why the progression of Purkinje cells loss is always from the anterior to the posterior lobes and why cerebellar defects persist in the mouse model even when genetic manipulations can lead to nearly normal survival.

Immune dysregulation, polyendocrinopathy and enteropathy, X-linked (IPEX) syndrome due to a mutation in FOXP3, modified by a pathogenic variant in SON (SON DNA-binding protein).

Immune dysregulation, polyendocrinopathy, enteropathy, and X-linked, known as IPEX syndrome, is a rare heterogeneous condition. Zhu-Tokita-Takenouchi-Kim Syndrome (ZTTK) is an autosomal dominant condition arising from a mutation in the SON gene, which is involved in mRNA splicing. A case showing interactions of mutations in these two genes is described in which both conditions become non-typical.

An explanation for the decreased severity of liver malfunction in Niemann-Pick C1 disease with age.

Niemann-Pick C disease frequently presents as severe cholestatic disease in infants. However, it progressively becomes less of a problem as children age. We have found that, in an appropriate mouse model, liver cholesterol levels, which are initially very high, decrease while mitochondrial function, initially quite compromised, increases with age. The key mitochondrial regulator, MNRR1, increases in parallel with the increase in mitochondrial function. These changes appear to explain the amelioration of the liver disease that occurs with time in this disorder.

Digenic Inheritance of a FOXC2 Mutation and Two PIEZO1 Mutations Underlies Congenital Lymphedema in a Multigeneration Family.

BACKGROUND: The lymphatic system is essential for maintaining the balance of interstitial fluid in tissues and for returning protein-rich fluids (lymph) to the bloodstream. Congenital lymphatic defects lead to accumulation of lymph in peripheral tissues and body cavities, termed primary lymphedema. To date, only a limited number of individual genes have been identified in association with primary lymphedema. However, variability of age of onset and severity of lymphatic abnormalities within some families suggests that multiple mutations or genes may be responsible, thus hampering efforts to identify individual associated genes. METHODS: Whole exome sequencing (WES) was performed in 4 members of a large multigeneration family with highly variable lymphedema and followed by Sanger sequencing for identified mutations in 34 additional family members. Genotypes were correlated with clinical and lymphangioscintigraphic phenotypes. RESULTS: WES uncovered 2 different mechanotransducer PIEZO1 mutations and one FOXC2 transcription factor mutation in various combinations. Sanger sequencing confirmed the presence/absence of the 3 variants in affected and unaffected family members and co-segregation of one or more variants with disease. Genetic profiles did not clearly correlate with the highly variable severity of lymphatic abnormalities. CONCLUSIONS: WES in lymphedema families can uncover unexpected combinations of several lymphedema-associated mutations. These findings provide essential information for genetic counseling and reveal complex gene interactions in lymphatic developmental pathways. These can offer insights into the complex spectrum of clinical and lymphatic lymphedema phenotypes and potential targets for treatment.

Primary lymphoedema.

Lymphoedema is the swelling of one or several parts of the body owing to lymph accumulation in the extracellular space. It is often chronic, worsens if untreated, predisposes to infections and causes an important reduction in quality of life. Primary lymphoedema (PLE) is thought to result from abnormal development and/or functioning of the lymphatic system, can present in isolation or as part of a syndrome, and can be present at birth or develop later in life. Mutations in numerous genes involved in the initial formation of lymphatic vessels (including valves) as well as in the growth and expansion of the lymphatic system and associated pathways have been identified in syndromic and non-syndromic forms of PLE. Thus, the current hypothesis is that most cases of PLE have a genetic origin, although a causative mutation is identified in only about one-third of affected individuals. Diagnosis relies on clinical presentation, imaging of the structure and functionality of the lymphatics, and in genetic analyses. Management aims at reducing or preventing swelling by compression therapy (with manual drainage, exercise and compressive garments) and, in carefully selected cases, by various surgical techniques. Individuals with PLE often have a reduced quality of life owing to the psychosocial and lifelong management burden associated with their chronic condition. Improved understanding of the underlying genetic origins of PLE will translate into more accurate diagnosis and prognosis and personalized treatment.

Autosomal recessive diseases among the Athabaskans of the southwestern United States: anthropological, medical, and scientific aspects.

The peopling of the Americas by Native Americans occurred in 4 waves of which the last was Nadene language speakers of whom Athabaskans are the largest group. As the Europeans were entering the Southwestern states of the USA, Athabaskan hunting-gathering tribes were migrating South from Canada along the Rocky Mountains and undergoing potential bottlenecks reflected in autosomal recessive diseases shared by Apaches and Navajos. About 300 years ago, the Navajo developing a sedentary culture learned from Pueblo Indians while the Apache remained hunter-gathers. Although most of the tribe was rounded up and forced to relocate to Bosque Redondo, the adult breeding population was large enough to prevent a genetic bottleneck. However, some Navajo underwent further population bottlenecks while hiding from the brutal US Army action (under Kit Carson's guidance). This led to an increased frequency of other autosomal recessive diseases. Recent advances in population genetics, pathophysiology of the diseases, and social/ethical issues concerning their study are reviewed.

Haploinsufficiency of tau decreases survival of the mouse model of Niemann-Pick disease type C1 but does not alter tau phosphorylation.

Niemann-Pick C1 (NPC1) mouse models show neurofibrillary tangles as do human patients. A previous study in NPC1/tau double-null mutant mice showed that tau knockout nulls and heterozygotes unexpectedly had decreased survival when compared with NPC1 single mutants (Pacheco et al., Hum Molec Genetics 18:956-965, 2009). This was done in a null model of NPC1 (Npc1-/-). We have extended these results to a hypomorphic model (Npc1nmf164) and additionally studied tau phosphorylation, which has not been previously done in a tau heterozygote. As before, NPC1/tau double-mutant mice had shortened survival when compared with the NPC1 single mutant. Tau dosage was not affected by the Npc1 mutation. The increased phosphorylation of tau-ser396 previously noted in NPC1 mouse models was also present, but unaffected by the tau knockout, indicating that changes in tau phosphorylation are not the cause of decreased survival in NPC1/tau double mutants. Thus, the reason for shortened survival of NPC1 mouse models with concomitant tau haploinsufficiency is uncertain.

Distribution and Diffusion of Macromolecule Delivery to the Brain via Focused Ultrasound using Magnetic Resonance and Multispectral Fluorescence Imaging.

Focused ultrasound (FUS), in combination with microbubble contrast agents, can be used to transiently open the blood-brain barrier (BBB) to allow intravascular agents to cross into the brain. Often, FUS is carried out in conjunction with magnetic resonance imaging (MRI) to evaluate BBB opening to gadolinium-based MRI contrast agents. Although MRI allows direct visualization of the distribution of gadolinium-based contrast agents in the brain parenchyma, it does not allow measurements of the distribution of other molecules crossing the BBB. Therapeutic molecules (e.g., monoclonal antibodies) are much different in size than MRI contrast agents and have been found to have different distributions in the brain after FUS-mediated BBB opening. In the work described here, we combined in vivo MRI and ex vivo multispectral fluorescence imaging to compare the distributions of MRI contrast and dextran molecules of different molecular weights (3, 70 and 500 kDa) after FUS-mediated BBB opening through a range of ultrasound pressures (0.18-0.46 MPa) in laboratory mice. The volume of brain exposed was calculated from the MRI and fluorescence images and was significantly dependent on both molecular weight and ultrasound pressure. Diffusion coefficients of the different-molecular-weight dextran molecules in the brain parenchyma were also calculated from the fluorescence images and were negatively correlated with the molecular weight of the dextran molecules. The results of this work build on a body of knowledge that is critically important for the FUS technique to be used in clinical delivery of therapeutics to the brain.

Decreased membrane cholesterol in liver mitochondria of the point mutation mouse model of juvenile Niemann-Pick C1, Npc1nmf164.

It has long been known that there is decreased mitochondrial function in several tissues of Niemann-Pick C1 model mice and cultured cells. These defects contribute to the accumulation of Reactive Oxygen Species (ROS) and tissue damage. It is also well established that there is increased unesterified cholesterol, stored in late endosomes/lysosomes, in many tissues in mutant humans, mouse models, and mutant cultured cells. Using a mouse model with an NPC1 point mutation that is more typical of the most common form of the disease, and highly purified liver mitochondria, we find markedly decreased mitochondrial membrane cholesterol. This is compared to previous reports of increased mitochondrial membrane cholesterol. We also find that, although in wild-type or heterozygous mitochondria cytochrome c oxidase (COX) activity decreases with age as expected, surprisingly, COX activity in homozygous mutant mice improves with age. COX activity is less than half of wild-type amounts in young mutant mice but later reaches wild-type levels while total liver cholesterol is decreasing. Mutant mice also contain a decreased number of mitochondria that are morphologically abnormal. We suggest that the decreased mitochondrial membrane cholesterol is causative for the mitochondrial energy defects. In addition, we find that the mitochondrial stress regulator protein MNRR1 can stimulate NPC1 synthesis and is deficient in mutant mouse livers. Furthermore, the age curve of MNRR1 deficiency paralleled levels of total cholesterol. The role of such altered mitochondria in initiating the abnormal autophagy and neuroinflammation found in NPC1 mouse models is discussed.

Decreased neural stem cell proliferation and olfaction in mouse models of Niemann-Pick C1 disease and the response to hydroxypropyl-ß-cyclodextrin.

The Npc1nih/nih-null model and the Npc1nmf164/nmf164 hypomorph models of Niemann-Pick C1 (NPC1) disease show defects in olfaction. We have tested the effects of the life-prolonging treatment hydroxypropyl-beta-cyclodextrin (HPBCD) on olfaction and neural stem cell numbers when delivered either systemically or by nasal inhalation. Using the paradigm of finding a hidden cube of food after overnight food deprivation, Npc1nih/nih homozygous mice showed a highly significant delay in finding the food compared with wild-type mice. Npc1nmf164/nmf164 homozygous mice showed an early loss of olfaction which was mildly corrected by somatic delivery of HPBCD which also increased the number of neural stem cells in the mutant but did not change the number in wild-type mice. In contrast, nasal delivery of this drug, at 1/5 the dosage used for somatic delivery, to Npc1nmf164/nmf164 mutant mice delayed loss of olfaction but the control of nasal delivered saline did so as well. The nasal delivery of HPBCD to wild-type mice caused loss of olfaction but nasal delivery of saline did not. Neural stem cell counts were not improved by nasal therapy with HPBCD. We credit the delay in olfaction found with the treatment, a delay which was also found for time of death, to a large amount of stimulation the mice received with handling during the nasal delivery.

Sex-limited penetrance of lymphedema to females with CELSR1 haploinsufficiency: A second family.

A second multigeneration family with hereditary lymphedema (LE) secondary to a variant in the planar polarity gene, CELSR1, is described. Dominant inheritance of the variant was discovered using whole-exome sequencing and confirmed by Sanger sequencing. In contrast to heterozygous males, all heterozygous females showed LE during physical examination albeit variable in severity and age of onset. Lymphscintigraphy in affected females showed previously undescribed lymphatic abnormalities consistent with lymphangiectasia, valve dysfunction, and thoracic duct reflux.

Co-treatment with probucol does not improve lung pathology in hydroxypropyl-ß-cyclodextrin-treated Npc1-/- mice.

We previously reported the altered pulmonary function and pathology found in the mouse model of infantile Niemann-Pick C1 disease, the Npc1-/- mouse. Despite its salutary properties on brain and liver parameters, we did not find efficacious effects of hydroxypropyl-ß-cyclodextrin (HPBCD) on pulmonary pathology. Since we had previously shown the beneficial effects of probucol on the somatic phenotype in the Npc1-/- mice, we have now studied the effects of combined therapy with HPBCD and probucol on the lung with mostly negative results. Body weight and lung weight for body weight were increased in parallel while inspiratory capacity for body weight was markedly decreased. Other physical, biochemical, and pulmonary function parameters were not much changed. There were trends towards improved lung elastance (p = 0.09) and compliance (p = 0.07).

Do GWAS and studies of heterozygotes for NPC1 and/or NPC2 explain why NPC disease cases are so rare?

Early onset Niemann-Pick C diseases are extremely rare, especially Niemann-Pick C2. Perhaps unusually for autosomal recessive diseases, heterozygotes for mutations in NPC1 manifest many biological variations. NPC2 deficiency has large effects on fertility. These features of NPC1 and NPC2 are reviewed in regard to possible negative selection for heterozygotes carrying null and hypomorphic alleles.

The pathogenesis of lysosomal storage disorders: beyond the engorgement of lysosomes to abnormal development and neuroinflammation.

There is growing evidence that the complex clinical manifestations of lysosomal storage diseases (LSDs) are not fully explained by the engorgement of the endosomal-autophagic-lysosomal system. In this review, we explore current knowledge of common pathogenetic mechanisms responsible for the early onset of tissue abnormalities of two LSDs, Mucopolysaccharidosis type II (MPSII) and Niemann-Pick type C (NPC) diseases. In particular, perturbations of the homeostasis of glycosaminoglycans (GAGs) and cholesterol (Chol) in MPSII and NPC diseases, respectively, affect key biological processes, including morphogen signaling. Both GAGs and Chol finely regulate the release, reception and tissue distribution of Shh. Hence, not surprisingly, developmental processes depending on correct Shh signaling have been found altered in both diseases. Besides abnormal signaling, exaggerated activation of microglia and impairment of autophagy and mitophagy occur in both diseases, largely before the appearance of typical pathological signs.

A pilot study of direct delivery of hydroxypropyl-beta-cyclodextrin to the lung by the nasal route in a mouse model of Niemann-Pick C1 disease: motor performance is unaltered and lung disease is worsened.

We have tested the efficacy of hydroxypropyl-beta-cyclodextrin (HPBCD) delivered by the nasal route in the mouse model of juvenile Niemann-Pick C1 disease (NPC1), as pulmonary disease has not responded to systemic therapy with this drug. Since mice have no gag reflex, coating of the nasal cavity, with possible access to the brain, would be followed by delivery of HPBCD to the lung. While foamy macrophages, containing stored cholesterol, were found in the Npc1 nmf164 homozygous mice, a marked inflammatory response was found with inhaled HPBCD, both in mutant and wild-type animals. Slight inflammation also occasionally occurred with saline inhalation. There was no difference between the saline-treated, HPBCD-treated, and untreated Npc1 nmf164 homozygous mice for weight, balance beam performance, or coat hanger performance. Interestingly, there was a trend to longer survival in the HPBCD-treated Npc1 nmf164 homozygous mice, which, when combined with the survival times of the saline-treated survivals (each of which was not different), became significant.

In Niemann-Pick C1 mouse models, glial-only expression of the normal gene extends survival much further than do changes in genetic background or treatment with hydroxypropyl-beta-cyclodextrin.

The Npc1nmf164 allele of Npc1 provides a mouse model for Niemann-Pick disease type C1 (NPC1), a genetic disease known to have a widely variable phenotype. The transfer of the Npc1nmf164 mutation from the C57BL/6J inbred strain to the BALB/cJ inbred strain increased the mean lifespan from 117.8days to 153.1days, confirming that the severity of the NPC1 phenotype is strongly influenced by genetic background. The transfer of another Npc1 allele, Npc1nih, to this background also extended survival of the homozygotes indicating that the modifying effect of BALB/cJ is not limited to a single allele of Npc1. The increased longevity due to the BALB/cJ background did not map to a previously mapped modifier on chromosome 19, indicating the presence of additional genes impacting disease severity. The previously studied Glial Fibrillary Acidic Protein promoter-Npc1 cDNA transgene (GFAP-Npc1) which only expresses NPC1 in astrocytes further extended the lifespan of Npc1nmf164 homozygotes on a BALB/cJ background (up to 600days). Hydroxypropyl-ß-cyclodextrin (HPßCD) treatment, not previously tested in the Npc1nmf164 mutant, extended life in the Npc1nmf164 homozygotes but not the transgenic, Npc1nmf164 mice on the BALB/cJ background. In all cases, lack of weight gain and early cerebellar symptoms of loss of motor control were found. At termination, the one mouse sacrificed for histological studies showed severe, diffuse pulmonary alveolar proteinosis suggesting that pulmonary abnormalities in NPC1 mouse models are not unique to the Npc1nih allele.