Skewing of X-chromosome inactivation in three generations of carriers with X-linked chronic granulomatous disease within one family

BACKGROUND: Chronic granulomatous disease (CGD) is an inherited disorder of the innate immune system characterized by impairment of intracellular microbicidal activity of phagocytes. Mutations in one of the four known NADPH-oxidase components preclude generation of superoxide and related antimicrobial oxidants, leading to the phenotype of CGD. Defects in gp91-phox, encoded by CYBB, lead to X-linked CGD, responsible for approximately 70% of all CGD cases. The aim of the study was to evaluate the hypothesis that age-related skewing of X-chromosome inactivation, as described in several CGD families, is caused by preferential survival of bone marrow clones with an inactive NADPH oxidase. MATERIALS AND METHODS: We studied the neutrophils from three patients and four carriers in three generations of a Turkish family with X-linked CGD. Carrier detection was carried out by the dihydrorhodamine (DHR)-1,2,3 assay, which measures on a per-cell basis the NADPH oxidase-dependent oxidation of DHR by phagocytes. The X-chromosome inactivation pattern was determined with the HUMARA assay in DNA from leucocytes as well as in DNA from a buccal smear of the four carriers. RESULTS: The three patients were identified by a negative DHR test, and the mutation in their CYBB gene was characterized by DNA sequencing. Moreover, we found an age-related degree of skewing of X-chromosome inactivation in the leucocytes of the four X-CGD carriers, both at the protein level (NADPH oxidase activity) and at the DNA level (HUMARA assay). However, similar skewing of X-chromosome inactivation was found in the buccal DNA from these women. CONCLUSIONS: These novel findings indicate that the age-related degree of skewing was probably a chance finding, not related to preferential survival of NADPH oxidase-deficient precursor cells, because this enzyme is not expressed in (buccal) epithelial cells.     

The CpG island of the FMR-1 gene is methylated differently among embryonic tissues: implication for prenatal diagnosis

We studied the methylation status of the CpG island of the FMR-1(fragile X syndrome) gene to recognize the possibility of itsprenatal diagnosis with early pregnant subjects. Southern hybridizationusing EcoRI/BssHII restriction enzymes double digestion wasperformed in the brain and chorionic villi of 8th week embryos,and the placenta and cord blood of newborns. No methylationof the FMR-1 gene occurred in both of the tissues examined inmales, while 50% of the cells in females were methylated inboth the brain and the cord blood, indicating that methylationoccurs with inactivation of the X-chromosome in accordance withthe literature. However, there was no methylation in eitherthe chorionic villi or placenta in female as well as in males.Some extra-embryonic tissues such as the chorionic villi andthe placenta escape X-chromosome FMR-1 gene inactivation andit can be the exception in the lyonization. To assess the methylationstatus in prenatal diagnosis, precautions are needed and theyare not suitable for prenatal diagnosis.     

Cytochemical flow analysis of intracellular G6PD and aggregate analysis of mosaic G6PD expression

Background

Medicines that exert oxidative pressure on red blood cells (RBC) can cause severe hemolysis in patients with glucose‐6‐phosphate dehydrogenase (G6PD) deficiency. Due to X‐chromosome inactivation, females heterozygous for G6PD with 1 allele encoding a G6PD‐deficient protein and the other a normal protein produce 2 RBC populations each expressing exclusively 1 allele. The G6PD mosaic is not captured with routine G6PD tests.

Methods

An open‐source software tool for G6PD cytofluorometric data interpretation is described. The tool interprets data in terms of % bright RBC, or cells with normal G6PD activity in specimens collected from 2 geographically and ethnically distinct populations, an African American cohort (USA) and a Karen and Burman ethnic cohort (Thailand) comprising 242 specimens including 89 heterozygous females.

Results

The tool allowed comparison of data across 2 laboratories and both populations. Hemizygous normal or deficient males and homozygous normal or deficient females cluster at narrow % bright cells with mean values of 96%, or 6% (males) and 97%, or 2% (females), respectively. Heterozygous females show a distribution of 10‐85% bright cells and a mean of 50%. The distributions are associated with the severity of the G6PD mutation.

Conclusions

Consistent cytofluorometric G6PD analysis facilitates interlaboratory comparison of cellular G6PD profiles and contributes to understanding primaquine‐associated hemolytic risk.     

Manifestation of the lines of Blaschko in women heterozygous for X-linked hypohidrotic ectodermal dysplasia

For the detection of the carrier state of X-linked hypohidrotic ectodermal dysplasia, sweat pore counts on fingertips or palms have been used in the past. The results obtained, however, were sometimes difficult to interpret. We here describe a more reliable method, using the entire back as a test area. We provide evidence that the distribution of sweat pores in carriers is not simply patchy. In four heterozygous women we were able to demonstrate a linear distribution of hypohidrotic areas. This pattern followed the lines of Blaschko, forming a typical V-shape over the spine. Apparently, these lines reflect the dorsoventral outgrowth of two functionally different populations of cells during early embryogenesis.     

Possible inactivation of part of chromosome 13 due to 13qXp translocation associated with retinoblastoma

Chromosome examination of a female patient with 13/X translocation associated with retinoblastoma was carried out using peripheral blood lymphocytes and cultured skin fibroblasts. The constitutional karyotype was 46,X,t(l 3;X) (q12;p22). Q-banding analysis showed that the translocated chromosomes were of paternal origin. Studies on DNA replication pattern with Giemsa banding using the bromodeoxyuridine substitution technique revealed that the derivative X chromosome was late replicating, and the translocated chromosome 13 was affected by the spreading of lyonization. Such a functional monosomy of 13q14 may also be involved in retinal blasts, and be related to the development of retinoblastoma.     

Expression of Properdin in Complete and Incomplete Deficiency: Normal in Vitro Synthesis by Monocytes in Two Cases with Properdin Deficiency Type II Due to Distinct Mutations

Three properdin deficiency phenotypes have been reported—complete deficiency (type I), incomplete deficiency (type II), and dysfunction of properdin protein (type III)—all associated with increased susceptibility to meningococcal disease. Expression of properdin by monocytes was examined in type I deficiency and in two unrelated cases with type II deficiency, one from a Swedish and one from a Danish family. The properdin gene in the Danish family contained a point mutation in exon 8 causing a Gln³¹⁶Arg substitution, distinct from a point mutation in exon 4 previously found in the Swedish family. Both genes coded for physicochemically abnormal properdin molecules with changed hydrophilicity. Monocytes from all the properdin-deficient individuals produced properdin mRNA in a normal fashion. In type I deficiency no intracellular or secreted properdin was found, indicating rapid intracellular degradation. Monocytes from the males with type II deficiency expressed and secreted properdin normally. Properdin in sera with type II deficiency showed abnormal oligomerization with a relative decrease in properdin trimers and tetramers. Our findings suggest that the low concentration of circulating properdin in type II deficiency is caused by increased extracellular catabolism. Analysis of properdin expression by mono-cytes in a female carrier in the family with properdin deficiency type I provided direct evidence of lyonization at the cellular level.     

X‐linked dominant protoporphyria: The first reported Japanese case

A 12‐year‐old boy with photosensitivity since 3 years of age presented with small concavities on both cheeks, the nasal root and the dorsal surface of both hands. According to the clinical features, erythropoietic protoporphyria (EPP) was suspected. Urine and blood samples were tested for porphyrin derivatives, which revealed a markedly elevated level of erythrocyte protoporphyrin (EP) and a diagnosis of EPP was made. The patient's mother had no photosensitivity, however, lesions appearing slightly as small scars were found on the dorsum of her right hand; his elder sister and father showed no rash. The EP levels were elevated in samples from his mother and mildly elevated in those from his elder sister and father. To obtain a definitive diagnosis, genetic analyses were performed using samples from all family members, which revealed no mutations in the ferrochelatase‐encoding gene (FECH), which is responsible for EPP. Instead, a pathological mutation of the 5‐aminolevulinic acid synthase‐encoding gene (ALAS2) was identified in samples from the patient, his mother and his elder sister, confirming a definitive diagnosis of X‐linked dominant protoporphyria (XLDPP). This is the first Japanese family reported to have XLDPP, demonstrating evidence of the condition in Japan. In addition, because XLDPP is very similar to EPP in its clinical aspects and laboratory findings, a genetic analysis is required for the differential diagnosis.     

Haemophilia B- in a girl

Summary. Haemophilia B is extremely rare in females and so far 20 cases have been reported. A 9-year-old girl with severe haemophilia symptoms is described, who shows a very low level of factor IX activity (1.5%) and antigen (> 10%), normal XX female karyotype and negative family history of bleeding tendency or consanguinity. This case is probably the fourth report of sporadic female haemophilia B without chromosomal aberration and the first one with quantitative analysis by immunoradiometric assay and enzyme-linked immunosorbent assay of factor IX antigen. This very low factor IX level and severe bleeding tendency of the patient would be consistent with the homozygous state, but since a double mutation is extremely rare the patient's laboratory findings can be more easily explained by extreme lyonization of the normal X-chromosome of a heterozygous carrier.