Case Report: Wiskott-Aldrich Syndrome Caused by Extremely Skewed X-Chromosome Inactivation in a Chinese Girl

Wiskott-Aldrich syndrome (WAS) is a rare X-linked immunodeficiency disorder caused by abnormal expression of Wiskott-Aldrich syndrome protein due to WAS gene mutation, which is generally characterized by microthrombocytopenia, eczema, recurrent infections, and high risk of autoimmune complications and hematological malignancies. Although affected males with WAS usually manifest severe symptoms, female carriers have no significant clinical manifestations. Here, we describe a Chinese girl diagnosed with WAS carrying a heterozygous missense mutation in exon 2 of the WAS gene. The patient presented with persistent thrombocytopenia with small platelets and decreased WAS protein detected by flow cytometry and western blot analysis. The methylation analysis of the HUMARA gene displayed an extremely skewed X-chromosome inactivation (SXCI) pattern, where the X-chromosomes bearing normal WAS gene were predominantly inactivated, leaving the mutant gene active. Hence, our results suggest that completely inactivating the unaffected paternal X-chromosomes may be the reason for such phenotype in this female patient. SXCI has important implications for genetic counseling of female carriers with a family history of WAS.

Lack of MECP2 gene transcription on the duplicated alleles of two MECP2 duplication females with opposite skewed X chromosome inactivation

Xq28 (involving MECP2) duplication syndrome is a severe neurodevelopmental disorder in males, most females are asymptomatic carriers, but there are phenotypic heterogeneities in the females. Skewed X-chromosome inactivation (XCI) seems to prevent duplicated region activation in asymptomatic females, but it remains controversial. Herein we reported two asymptomatic females (daughter and mother) with interstitial Xq28 duplication. HUMARA and RP2 assays showed that both had complete skewed XCI, the Xq28 duplicated chromosome was inactivated in the daughter, but surprisingly, it was activated in her mother. Interestingly, by combining RNA sequencing and whole-exome sequencing, we confirmed that XIST only expressed in the Xq28 duplication chromosomes of the two females, indicating that the Xq28 duplication chromosomes were inactive. Meanwhile, MECP2 and most XCI genes in the duplicated X-chromosomes were not transcriptionally expressed or upregulated, precluding major clinical phenotypes in the two females, especially the mother. We showed that XCI status detected by RNA sequencing was more relevant for establishing the clinical phenotype of MECP2 duplication females. It suggested there were other factors maintaining the XCI status in addition to DNA methylation, a possible additional inhibition mechanism occured at the transcriptional level in the unmethylated X-chromosome, counter balancing the MECP2 duplication’s detrimental phenotype effects

Late-onset X-linked Chronic Granulomatous Disease in a Female Carrier: Therapeutic Role of Interferon-γ and Hematopoietic Stem Cell Transplantation

X-linked Chronic Granulomatous Disease (CGD) is a rare inherited immunodeficiency characterized by early life-threatening infections from bacteria and fungi in male children. Female carriers of X-linked CGD usually do not develop any manifestations of the disease, yet in rare cases they may present with CGD-related manifestations due to skewed X chromosome inactivation, even in advanced age. Here, we report the case of a 49-year-old woman with no history of previous frequent or severe infections, who presented acutely with life-threatening bilateral pneumonia caused by Nocardia asteroides and was eventually diagnosed with late-onset X-linked CGD due to skewed X chromosome inactivation in white blood cells. Treatment with interferon-γ as a rescue therapy resulted in normalization of the intensity of the oxidative burst in the residual positive cells and resolution of the infection, which was otherwise resistant to conventional treatments. After discharge, however, recurrent severe pulmonary infections despite prophylactic treatments as well as appearance of granulomatous colitis led to considering definitive treatment. Hematopoietic stem cell transplantation from unaffected HLA-identical brother using a non-myeloablative conditioning protocol with intravenous busulfan followed by high-dose peripheral blood stem cell graft and post-transplant cyclophosphamide was successfully performed. After three years of follow-up, white blood cell chimerism remained stable with about 60% donor cells in the myeloid lineage, with no further infections and no recurrence of inflammatory bowel disease.

Skewness of X-chromosome inactivation increases with age and varies across birth cohorts in elderly Danish women

Mosaicism in blood varies with age, and cross-sectional studies indicate that for women, skewness of X-chromosomal mosaicism increases with age. This pattern could, however, also be due to less X-inactivation in more recent birth cohorts. Skewed X-chromosome inactivation was here measured longitudinally by the HUMARA assay in 67 septuagenarian and octogenarian women assessed at 2 time points, 10 years apart, and in 10 centenarian women assessed at 2 time points, 2–7 years apart. Skewed X-chromosome inactivation was also compared in 293 age-matched septuagenarian twins born in 1917–1923 and 1931–1937, and 212 centenarians born in 1895, 1905 and 1915. The longitudinal study of septuagenarians and octogenarians revealed that 16% (95% CI 7–29%) of the women developed skewed X-inactivation over a 10-year period. In the cross-sectional across-birth cohort study, the earlier-born septuagenarian (1917–1923) and centenarian women (1895) had a higher degree of skewness than the respective recent age-matched birth cohorts, which indicates that the women in the more recent cohorts, after the age of 70, had not only changed degree of skewness with age, they had also undergone less age-related hematopoietic sub-clone expansion. This may be a result of improved living conditions and better medical treatment in the more recent birth cohorts.

X-linked CNV and skewed X-chromosome inactivation

Смещение инактивации Х-хромосомы может быть следствием и маркером нарушения клеточной пролиферации при вариациях числа копий ДНК на Х-хромосоме. Х-сцепленные CNV выявляются как у женщин с невынашиванием беременности и смещением инактивации Х-хромосомы (с частотой 33,3%), так и у пациентов с умственной отсталостью и смещением инактивацией у их матерей (с частотой 40%). A skewed X-chromosome inactivation can be a consequence and a marker of impaired cell proliferation in the presence of copy number variations (CNV) on the X chromosome. X-linked CNVs are detected in women with miscarriages and a skewed X-chromosome inactivation (with a frequency of 33.3%), as well as in patients with intellectual disability and skewed X-chromosome inactivation in their mothers (with a frequency of 40%).

Etiology and Risk Factors

The etiology of Hashimoto's thyroiditis (HT) arises from an interaction between genetic and non-genetic factors. The genes implicated vary in different ethnic groups and the incidence is increased in people with chromosomal disorders. HT is usually associated with auto-antibodies against thyroglobulin (Tg) and thyro-perioxidase (TPO) leading to primary hypothyroidism. Having other autoimmune diseases is a risk factor to develop HT. First-degree relatives of persons with HT have greater risk of developing the disease. Female gender is associated with an eight-fold increased risk for HT possibly due to the effects of sex hormones, X-chromosome-encoded susceptibility, skewed X-chromosome inactivation, pregnancy, and fetal micro-chimerism. In genetically susceptible individuals, environmental factors, including high iodine intake, selenium deficiency, infectious diseases, stress, and certain drugs, have been implicated in initiating the autoimmune process. This chapter explores the etiology and risk factors of Hashimoto's disease.