Causes of infertility in men with Down syndrome

Low bone mass and impaired fracture healing in mouse models of Trisomy21 (Down syndrome)

Individuals with Down syndrome (DS), the result of trisomy of human chromosome Hsa21 (Ts21), present with an array of skeletal abnormalities typified by altered craniofacial features, short stature and low bone mineral density (BMD). While bone deficits progress with age in both sexes, low bone mass is more pronounced in DS men than women and osteopenia appears earlier. In the current study, the reproductive hormone status (FSH, LH, testosterone) of 17 DS patients (males, ages range 19-52 years) was measured. Although testosterone was consistently low, the hypothalamic-pituitary-gonadal axis was intact with corresponding rises in FSH and LH. To provide further insight into the heterogeneity of the bone mass in DS, the skeletal phenotypes of three of the most used murine DS models, Ts65Dn (Ts65), TC1, and Dp16(Yey1) (Dp16) were characterized and contrasted. Evaluation of the bone phenotype of both male and female 3-month-old Dp16 mice demonstrated sexual dimorphism, with low bone mass apparent in males, as it is in Ts65, but not in female Dp16. In contrast, male TC1 mice had no apparent bone phenotype. To determine whether low bone mass in DS impacted fracture healing, fractures of the middle phalanx (P2) digits were generated in both male and female Dp16 mice at 15 weeks of age, an age where the sexually dimorphic low BMD persisted. Fracture healing was assessed via in vivo microCT over (13 weeks) 93 days post fracture (DPF). At 93 DPF, 0 % of DS male (n = 12) or female (n = 8) fractures healed, compared to 50 % of the male (n = 28) or female (n = 8) WT littermate fractures. MicroCT revealed periosteal unbridged mineralized callus formation across the fracture gap in Dp16 mice, which was confirmed by subsequent histology. These studies provide the first direct evidence of significantly impaired fracture healing in the setting of DS.

Clinical Profiles, Congenital Heart Disease, and Other Comorbidities Among Egyptian Children with Down Syndrome: A Tertiary Center Study

Introduction Down syndrome (DS) is the most common chromosomal disorder. It is accompanied by several comorbidities, which could lead to severe morbidity and mortality. Congenital heart disease (CHD) is one of the most commonly described condition.

Objective This study aimed to determine clinical profiles, dysmorphic features, CHD, and DS associated comorbidities in a tertiary center (Cairo, Egypt).

Patients and Methods This descriptive study included 290 patients diagnosed with DS, who presented to the Clinical Genetics clinic, Cairo University Children Hospitals, from February 2018 to December 2019. The patients' ages ranged from 2 to 4 years old. All patients were evaluated by full history, clinical examination, anthropometric measurements, and assessment of developmental milestones. Patients' diagnostic investigations including karyotype, thyroid function, and echocardiography were checked.

Results The study population consisted of 290 children with DS of which 196 (67.6%) were male, 115 (40%) had CHD, the most prevalent atrial septal defect (ASD), patent ductus arteriosus (PDA), and ventricular septal defect (VSD) accounting for 10.7, 7.1, and 4.2%, respectively. Common dysmorphic features were upward slanting palpebral fissures (98.6%), hypertelorism (97.9%), and sandal gap (60.7%). Thyroid dysfunction was the second prevalent comorbidity, found in 35 patients (12.1%). Global developmental delay was reported affecting language (99%), motor (94.8%), and social (92.8%) domains.

Conclusion The prevalence of CHD among children with DS was 40% with ASD, PDA, and VSD being the commonest. Thyroid dysfunction was the second most common comorbidity. The most prevalent dysmorphic features were upward slanting palpebral fissures, hypertelorism, and sandal gap. Developmental delay was very common, language being the most affected domain.

Detection of a Recurrent TMEM38B Gene Deletion Associated with Recessive Osteogenesis Imperfecta

Osteogenesis imperfecta is a clinically and genetically group of heterogeneous disorders associated with decreased bone density, brittle bones, bone deformity, recurrent fractures, and growth retardation. Osteogenesis imperfecta is commonly associated with mutations of the genes encoding for type I collagen (COL1A1/COL1A2). Mutations in other genes, some associated with type I collagen post-translational processing, have also been identified as the cause of osteogenesis imperfecta. Mutations in the transmembrane protein 38B (TMEM38B) gene have been reported in a rare autosomal recessive form of osteogenesis imperfecta.  TMEM38B encodes TRIC-B - a trimeric intracellular cation channel type B which is essential to modulate intracellular calcium signaling. In this study, we are reporting a case of osteogenesis imperfecta type XIV from a Saudi consanguineous family. Our patient was an eight-month-old child with short limbs, club feet, and lower limb deformities with developmental delay. Radiological findings were consistent with the evidence of osteogenesis imperfecta. There was no evidence of impaired hearing or blue sclera and based on the clinical assessment, we classified our patient as a non-syndromic osteogenesis imperfecta. A pathogenic deletion in the chromosome 9q31.2 region, partially encompassing the TMEM38B gene, was detected using chromosomal microarray analysis. This study expands our knowledge about the rare type of osteogenesis imperfecta in our consanguineous population. Besides, it emphasizes the use of genomic medicine in clinical practices to formulate early interventions to clinically improve the patient’s condition.

Down syndrome

Trisomy 21, the presence of a supernumerary chromosome 21, results in a collection of clinical features commonly known as Down syndrome (DS). DS is among the most genetically complex of the conditions that are compatible with human survival post-term, and the most frequent survivable autosomal aneuploidy. Mouse models of DS, involving trisomy of all or part of human chromosome 21 or orthologous mouse genomic regions, are providing valuable insights into the contribution of triplicated genes or groups of genes to the many clinical manifestations in DS. This endeavour is challenging, as there are >200 protein-coding genes on chromosome 21 and they can have direct and indirect effects on homeostasis in cells, tissues, organs and systems. Although this complexity poses formidable challenges to understanding the underlying molecular basis for each of the many clinical features of DS, it also provides opportunities for improving understanding of genetic mechanisms underlying the development and function of many cell types, tissues, organs and systems. Since the first description of trisomy 21, we have learned much about intellectual disability and genetic risk factors for congenital heart disease. The lower occurrence of solid tumours in individuals with DS supports the identification of chromosome 21 genes that protect against cancer when overexpressed. The universal occurrence of the histopathology of Alzheimer disease and the high prevalence of dementia in DS are providing insights into the pathology and treatment of Alzheimer disease. Clinical trials to ameliorate intellectual disability in DS signal a new era in which therapeutic interventions based on knowledge of the molecular pathophysiology of DS can now be explored; these efforts provide reasonable hope for the future.

A male Down syndrome with two normal boys: Cytogenetic, paternity and andrological investigations

Down syndrome is the most common autosomal chromosome anomaly with several medical abnormalities and intellectual disability, occurring in about of 1:1,000 to 1:1,100 infants. Many pregnancies in women with Down syndrome produce children both with normal and with trisomy 21, whereas males are infertile. However, Down syndrome males are not always infertile and this is not global. Here we reported a 36-year-old man with proved nonmosaic trisomy 21 fathered two normal boys. Paternity analysis using 26 microsatellite loci confirmed that Down syndrome male is the biological father of his two normal boys. Serum LH, FSH, testosterone and 17-OH progesterone were all in the normal range in this father with Down syndrome. To the best of our knowledge, this is the second report of one man with Down syndrome who has two normal children in the world. The current study not only supports the rare evidence of the fertility of males with Down syndrome but also highlights the caution in advising people responsible for the care of adults with this condition about possible fertility and transmission of sexual diseases as well.

Testicular endothelial cells are a critical population in the germline stem cell niche

Maintenance of adult tissues depends on stem cell self-renewal in local niches. Spermatogonial stem cells (SSC) are germline adult stem cells necessary for spermatogenesis and fertility. We show that testicular endothelial cells (TECs) are part of the SSC niche producing glial cell line-derived neurotrophic factor (GDNF) and other factors to support human and mouse SSCs in long-term culture. We demonstrate that FGF-2 binding to FGFR1 on TECs activates the calcineurin pathway to produce GDNF. Comparison of the TEC secretome to lung and liver endothelial cells identified 5 factors sufficient for long-term maintenance of human and mouse SSC colonies in feeder-free cultures. Male cancer survivors after chemotherapy are often infertile since SSCs are highly susceptible to cytotoxic injury. Transplantation of TECs alone restores spermatogenesis in mice after chemotherapy-induced depletion of SSCs. Identifying TECs as a niche population necessary for SSC self-renewal may facilitate fertility preservation for prepubertal boys diagnosed with cancer.

Self-renewal of spermatogonial stem cells (SSC) is necessary for spermatogenesis and male fertility. Here the authors identify testicular endothelial cells (TECs) as a source of 5 key growth factors for self-renewal and expansion of human and mouse SSCs.

Aneuploidy and skeletal health

The normal human chromosome complement consists of 46 chromosomes comprising 22 morphologically different pairs of autosomes and one pair of sex chromosomes. Variations in either chromosome number and/or structure frequently result in significant mental impairment and/or a variety of other clinical problems, among them, altered bone mass and strength. Chromosomal syndromes associated with specific chromosomal abnormalities are classified as either numerical or structural and may involve more than one chromosome. Aneuploidy refers to the presence of an extra copy of a specific chromosome, or trisomy, as seen in Down's syndrome (trisomy 21), or the absence of a single chromosome, or monosomy, as seen in Turner syndrome (a single X chromosome in females: 45, X). Aneuploidies have diverse phenotypic consequences, ranging from severe mental retardation and developmental abnormalities to increased susceptibility to various neoplasms and premature death. In fact, trisomy 21 is the prototypical aneuploidy in humans, is the most common genetic abnormality associated with longevity, and is one of the most widespread genetic causes of intellectual disability. In this review, the impact of trisomy 21 on the bone mass, architecture, skeletal health, and quality of life of people with Down syndrome will be discussed.

Low bone turnover and low BMD in Down syndrome: effect of intermittent PTH treatment

Trisomy 21 affects virtually every organ system and results in the complex clinical presentation of Down syndrome (DS). Patterns of differences are now being recognized as patients' age and these patterns bring about new opportunities for disease prevention and treatment. Low bone mineral density (BMD) has been reported in many studies of males and females with DS yet the specific effects of trisomy 21 on the skeleton remain poorly defined. Therefore we determined the bone phenotype and measured bone turnover markers in the murine DS model Ts65Dn. Male Ts65Dn DS mice are infertile and display a profound low bone mass phenotype that deteriorates with age. The low bone mass was correlated with significantly decreased osteoblast and osteoclast development, decreased bone biochemical markers, a diminished bone formation rate and reduced mechanical strength. The low bone mass observed in 3 month old Ts65Dn mice was significantly increased after 4 weeks of intermittent PTH treatment. These studies provide novel insight into the cause of the profound bone fragility in DS and identify PTH as a potential anabolic agent in the adult low bone mass DS population.