The mean height is taller in males than in females, except for early teens. In this regard, previous studies have revealed that (1) distribution of the mean adult heights in subjects with disorders accompanied by discordance between sex chromosome complement and bioactive sex steroids and in control subjects (the British height standards) indicates that, of the ~12.5 cm of sex difference in the mean adult height, ~9 cm is accounted for by the difference in the sex chromosome complement and the remaining ~3.5 cm is explained by the dimorphism in sex steroids (primarily due to the growth-promoting effect of gonadal androgens); (2) according to the infancy-childhood-puberty growth model, the sex difference in the childhood growth function produces height differences of ~1 cm in childhood and 8-10 cm at 18-20 years of age, whereas the sex difference in the pubertal growth function yields height difference of ~4.5 cm at 18-20 years of age; and (3) SHOX expression and methylation analyses using knee cartilage tissues and cultured chondrocytes have shown lower SHOX expression levels in female samples than in male samples and methylation patterns consistent with partial spreading of X-inactivation affecting SHOX in female samples. These findings suggest that small but persistent sex difference in SHOX expression dosage leads to the variation in the sex steroid independent childhood growth function, thereby yielding the sex difference in height which remains small in childhood but becomes obvious in adulthood.

The linear DNA sequence of mammalian chromosomes is organized in large blocks of DNA with similar sequence properties, producing a pattern of dark and light staining bands on mitotic chromosomes. Cytogenetic banding is essentially invariant between people and cell-types and thus may be assumed unrelated to genome regulation. We investigate whether large blocks of Alu-rich R-bands and L1-rich G-bands provide a framework upon which functional genome architecture is built. We examine two models of large-scale chromatin condensation: X-chromosome inactivation and formation of senescence-associated heterochromatin foci (SAHFs). XIST RNA triggers gene silencing but also formation of the condensed Barr Body (BB), thought to reflect cumulative gene silencing. However, we find Alu-rich regions are depleted from the L1-rich BB, supporting it is a dense core but not the entire chromosome. Alu-rich bands are also gene-rich, affirming our earlier findings that genes localize at the outer periphery of the BB. SAHFs similarly form within each territory by coalescence of syntenic L1 regions depleted for highly Alu-rich DNA. Analysis of senescent cell Hi-C data also shows large contiguous blocks of G-band and R-band DNA remodel as a segmental unit. Entire dark-bands gain distal intrachromosomal interactions as L1-rich regions form the SAHF. Most striking is that sharp Alu peaks within R-bands resist these changes in condensation. We further show that Chr19, which is exceptionally Alu rich, fails to form a SAHF. Collective results show regulation of genome architecture corresponding to large blocks of DNA and demonstrate resistance of segments with high Alu to chromosome condensation.

Dystrophinopathies are the most common muscle diseases, especially in men. In women, on the other hand, a manifestation of Duchenne muscular dystrophy is rare due to X-chromosomal inheritance. We present two young girls with severe muscle weakness, muscular dystrophies, and creatine kinase (CK) levels exceeding 10,000 U/L. In the skeletal muscle tissues, dystrophin staining reaction showed mosaicism. The almost entirely skewed X-inactivation in both cases supported the possibility of a dystrophinopathy. Despite standard molecular diagnostics (including multiplex ligation-dependent probe amplification (MLPA) and next generation sequencing (NGS) gene panel sequencing), the genetic cause of the girls\' conditions remained unknown. However, whole-genome sequencing revealed two reciprocal translocations between their X chromosomes and chromosome 5 and chromosome 19, respectively. In both cases, the breakpoints on the X chromosomes were located directly within the DMD gene (in introns 54 and 7, respectively) and were responsible for the patients\' phenotypes. Additional techniques such as Sanger sequencing, conventional karyotyping and fluorescence in situ hybridization (FISH) confirmed the disruption of DMD gene in both patients through translocations. These findings underscore the importance of accurate clinical data combined with histopathological analysis in pinpointing the suspected underlying genetic disorder. Moreover, our study illustrates the viability of whole-genome sequencing as a time-saving and highly effective method for identifying genetic factors responsible for complex genetic constellations in Duchenne muscular dystrophy (DMD).

X-linked retinoschisis (XLRS) is the most common juvenile macular degeneration in males. Unlike most other X-linked retinal dystrophies, carrier heterozygous females are very rarely reported to show clinical features of the disease. Herein, we describe unusual retinal features in a 2-year-old female infant with family history and genetic testing consistent with XLRS.

Realization of the immense therapeutic potential of epigenetic editing requires development of clinically predictive model systems that faithfully recapitulate relevant aspects of the target disease pathophysiology. In female patients with ornithine transcarbamylase (OTC) deficiency, an X-linked condition, skewed inactivation of the X chromosome carrying the wild-type OTC allele is associated with increased disease severity. The majority of affected female patients can be managed medically, but a proportion require liver transplantation. With rapid development of epigenetic editing technology, reactivation of silenced wild-type OTC alleles is becoming an increasingly plausible therapeutic approach. Toward this end, privileged access to explanted diseased livers from two affected female infants provided the opportunity to explore whether engraftment and expansion of dissociated patient-derived hepatocytes in the FRG mouse might produce a relevant model for evaluation of epigenetic interventions. Hepatocytes from both infants were successfully used to generate chimeric mouse-human livers, in which clusters of primary human hepatocytes were either OTC positive or negative by immunohistochemistry (IHC), consistent with clonal expansion from individual hepatocytes in which the mutant or wild-type OTC allele was inactivated, respectively. Enumeration of the proportion of OTC-positive or -negative human hepatocyte clusters was consistent with dramatic skewing in one infant and minimal to modest skewing in the other. Importantly, IHC and fluorescence-activated cell sorting analysis of intact and dissociated liver samples from both infants showed qualitatively similar patterns, confirming that the chimeric mouse-human liver model recapitulated the native state in each infant. Also of importance was the induction of a treatable metabolic phenotype, orotic aciduria, in mice, which correlated with the presence of clonally expanded OTC-negative primary human hepatocytes. We are currently using this unique model to explore CRISPR-dCas9-based epigenetic targeting strategies in combination with efficient adeno-associated virus (AAV) gene delivery to reactivate the silenced functional OTC gene on the inactive X chromosome.

Reactivation of the inactive X chromosome is a hallmark epigenetic event during reprogramming of mouse female somatic cells to induced pluripotent stem cells (iPSCs). This involves global structural remodeling from a condensed, heterochromatic into an open, euchromatic state, thereby changing a transcriptionally inactive into an active chromosome. Despite recent advances, very little is currently known about the molecular players mediating this process and how this relates to iPSC-reprogramming in general. To gain more insight, here we perform a RNAi-based knockdown screen during iPSC-reprogramming of mouse fibroblasts. We discover factors important for X chromosome reactivation (XCR) and iPSC-reprogramming. Among those, we identify the cohesin complex member SMC1a as a key molecule with a specific function in XCR, as its knockdown greatly affects XCR without interfering with iPSC-reprogramming. Using super-resolution microscopy, we find SMC1a to be preferentially enriched on the active compared with the inactive X chromosome and that SMC1a is critical for the decompacted state of the active X. Specifically, depletion of SMC1a leads to contraction of the active X both in differentiated and in pluripotent cells, where it normally is in its most open state. In summary, we reveal cohesin as a key factor for remodeling of the X chromosome from an inactive to an active structure and that this is a critical step for XCR during iPSC-reprogramming.

BACKGROUND: Osteopathia Striata with Cranial Sclerosis (OS-CS), also known as Horan-Beighton Syndrome, is a rare genetic disease; about 90 cases have been reported to date. It is associated with mutations (heterozygous for female subjects and hemizygous for males) of the AMER1 gene, located at Xq11.2, and shows an X-linked pattern of transmission. Typical clinical manifestations include macrocephaly, characteristic facial features (frontal bossing, epicanthal folds, hypertelorism, depressed nasal bridge, orofacial cleft, prominent jaw), hearing loss and developmental delay. Males usually present a more severe phenotype than females and rarely survive. Diagnostic suspicion is based on clinical signs, radiographic findings of cranial and long bones sclerosis and metaphyseal striations, subsequent genetic testing may confirm it.
METHODS: Hereby, we report on a female newborn with frontal and parietal bossing, narrow bitemporal diameter, dysplastic, low-set and posteriorly rotated ears, microretrognathia, cleft palate, and rhizomelic shortening of lower limbs. Postnatally, she manifested feeding intolerance with biliary vomiting and abdominal distension. Therefore, in the suspicion of bowel obstruction, she underwent surgery, which evidenced and corrected an intestinal malrotation. Limbs X-ray and skull computed tomography investigations did not show cranial sclerosis and/or metaphyseal striations. Array-CGH analysis revealed normal findings. Then, a target next generation sequencing (NGS) analysis, including the genes involved in skeletal dysplasias, was performed and revealed a de novo heterozygous nonsense mutation of the AMER1 gene. The patient was discharged at 2 months of age and included in a multidisciplinary follow-up. Aged 9 months, she now shows developmental and growth (except for relative macrocephaly) delay. The surgical correction of cleft palate has been planned.
CONCLUSIONS: Our report shows the uncommon association of intestinal malrotation in a female newborn with OS-CS. It highlights that neonatologists have to consider such a diagnosis, even in absence of cranial sclerosis and long bones striations, as these usually appear over time. Other syndromes with cranial malformations and skeletal dysplasia must be included in the differential diagnosis. The phenotypic spectrum is wide and variable in both genders. Due to variable X-inactivation, females may also show a severe and early-onset clinical picture. Multidisciplinary management and careful, early and long-term follow-up should be offered to these patients, in order to promptly identify any associated morbidities and prevent possible complications or adverse outcomes.

Wiskott-Aldrich syndrome (WAS) is an X-linked immunodeficiency characterized by thrombocytopenia and eczema and is caused by a mutation in the WAS gene. WAS has heterogeneous clinical manifestations, and its clinically milder form is called X-linked thrombocytopenia (XLT). Patients with WAS/XLT sometimes have kidney complications, the most common of which is immunoglobulin (Ig)A nephropathy associated with aberrant glycosylation of IgA.
The patient was a 6-year-old girl who was diagnosed with female XLT at the age of 4 years; she presented with microscopic hematuria and proteinuria at a school urinalysis. Her father had thrombocytopenia and IgA nephropathy while in his 20 s. The patient and her father had the same WAS gene mutations. A kidney biopsy was performed, and no abnormal findings were observed by light microscopy. Immunofluorescence analysis revealed a granular pattern of IgG staining along the capillary wall. Electron microscopy revealed small electron-dense deposits in subepithelial lesions. Consequently, we diagnosed her with membranous nephropathy (MN). Tissue PLA2R and THSD7A were negative, and she was judged unlikely to have secondary MN on the basis of blood test findings and IgG staining. We started the administration of angiotensin-converting enzyme inhibitors, and her proteinuria gradually decreased.
To our knowledge, this is the first report of MN in a female WAS/XLT patient. WAS protein expression defects affect all immune system cells; however, the mechanisms underlying the occurrence of autoimmunity are not completely understood. In WAS/XLT patients, MN may develop as a result of increased autoantibody production, similar to other types of immunodeficiency.

Although women experience significantly higher tau burden and increased risk for Alzheimer\'s disease (AD) than men, the underlying mechanism for this vulnerability has not been explained. Here, we demonstrate through in vitro and in vivo models, as well as human AD brain tissue, that X-linked ubiquitin specific peptidase 11 (USP11) augments pathological tau aggregation via tau deubiquitination initiated at lysine-281. Removal of ubiquitin provides access for enzymatic tau acetylation at lysines 281 and 274. USP11 escapes complete X-inactivation, and female mice and people both exhibit higher USP11 levels than males. Genetic elimination of usp11 in a tauopathy mouse model preferentially protects females from acetylated tau accumulation, tau pathology, and cognitive impairment. USP11 levels also strongly associate positively with tau pathology in females but not males. Thus, inhibiting USP11-mediated tau deubiquitination may provide an effective therapeutic opportunity to protect women from increased vulnerability to AD and other tauopathies.

The spatial organization of genomes is becoming increasingly understood. In mammals, where it is most investigated, this organization ties in with transcription, so an important research objective is to understand whether gene activity is a cause or a consequence of genome folding in space. In this regard, the phenomena of X-chromosome inactivation and reactivation open a unique window of investigation because of the singularities of the inactive X chromosome. Here we focus on the cause-consequence nexus between genome conformation and transcription and explain how recent results about the structural changes associated with inactivation and reactivation of the X chromosome shed light on this problem.