X-chromosomal Polymorphisms Research Articles

Twenty Years Later: A Comprehensive Review of the X Chromosome Use in Forensic Genetics.

The unique structure of the X chromosome shaped by evolution has led to the present gender-specific genetic differences, which are not shared by its counterpart, the Y chromosome, and neither by the autosomes. In males, recombination between the X and Y chromosomes is limited to the pseudoautosomal regions, PAR1 and PAR2; therefore, in males, the X chromosome is (almost) entirely transmitted to female offspring. On the other hand, the X chromosome is present in females with two copies that recombine along the whole chromosome during female meiosis and that is transmitted to both female and male descendants. These transmission characteristics, besides the obvious clinical impact (sex chromosome aneuploidies are extremely frequent), make the X chromosome an irreplaceable genetic tool for population genetic-based studies as well as for kinship and forensic investigations. In the early 2000s, the number of publications using X-chromosomal polymorphisms in forensic and population genetic applications increased steadily. However, nearly 20 years later, we observe a conspicuous decrease in the rate of these publications. In light of this observation, the main aim of this article is to provide a comprehensive review of the advances and applications of X-chromosomal markers in population and forensic genetics over the last two decades. The foremost relevant topics are addressed as: (i) developments concerning the number and types of markers available, with special emphasis on short tandem repeat (STR) polymorphisms (STR nomenclatures and practical concerns); (ii) overview of worldwide population (frequency) data; (iii) the use of X-chromosomal markers in (complex) kinship testing and the forensic statistical evaluation of evidence; (iv) segregation and mutation studies; and (v) current weaknesses and future prospects.

Taxonomic status of the black fly Prosimulium italicum Rivosecchi(Diptera: Simuliidae) based on genetic evidence.

The black fly Prosimulium italicum Rivosecchi, distributed in the Apennines and Sicily, was described as a subspecies of Prosimulium hirtipes (Fries), based on a few morphological details. It subsequently was considered conspecific with P. hirtipes and the name was synonymized. Analyses of polytene chromosome banding patterns and sequences of mitochondrial DNA (COI and COII) revealed deep genetic divergence between P. italicum from Italy and P. hirtipes from northern and central Europe and confirmed the species status of P. italicum. Populations of P. italicum either lack chromosomal inversion IS-9 or carry it as an X-chromosome polymorphism, whereas all analyzed populations of P. hirtipes (Slovakia, Sweden, England, and Scotland) are fixed for IS-9. The average K2P genetic distance was 3.7% between P. italicum and P. hirtipes from northern Europe (Sweden) and 4.3 % between P. italicum and P. hirtipes from central Europe (Slovakia). Cytogenetic analysis showed the presence of two cytoforms of P. hirtipes ('A' in Sweden and Slovakia and 'B' in England and Scotland) and two cytoforms of P. italicum ('A' in Sicily and 'B' in Campania and Basilicata), all of which differ in their sex chromosomes and autosomal polymorphisms, suggesting that P. hirtipes and P. italicum might each be a complex of cryptic species.

X-chromosome polymorphism on DXS8378, DXS7132, HPRTB and DXS7423 loci in 130 individuals from Brescia (northern Italy)

One hundred and thirty unrelated individuals (80 females and 50 males) from Brescia (northern Italy) were typed for DXS8378, DXS7132, HPRTB and DXS7423 loci. Allele, genotype and haplotype frequencies were calculated. A comparison between our population data and others from Caucasians and Asians populations was performed.

Myelofibrosis in a Patient with Sarcoidosis.

Secondary bone marrow fibrosis can be seen in several conditions such as hematological malignancy, metastatic malignancy and autoimmune disorders like lupus. We report here a 50 year old Middle Eastern female with a history of pulmonary sarcoidosis diagnosed by lung biopsy in January of 2004, beta thalassemia trait, hypertension and hypothyroidism. At the time of diagnosis she was started on bronchodilating inhalers. Nine months later she was referred to hematology for left lower quadrant pain and possible enlarged spleen on examination. CT scan revealed extensive mediastinal, retroperitoneal and inguinal adenopathy but no splenomegaly. Hemoglobin was 12.3 with a hematocrit of 38 and an MCV of 61, WBC was 7.8with a normal differential and Platelet count was 238. Her peripheral blood smear revealed moderate anisocytosis, polychromasia and some teardrops. Bone marrow biopsy showed significant fibrosis confirmed by reticulin staining. Biopsy of an inguinal node was consistent with her lung biopsy showing granulomatous disease. In the course of follow up she developed fever, fatigue, anemia, and splenomegaly proven by ultrasound (16cm). Her labs also revealed increased ACE and ESR levels. We started her on prednisone at 1mg/kg and her hemoglobin rose from 8.0 to 12.5. X-chromosome transcription-based clonality assays were employed to deteremine whether this patient had primary myelofibrosis with myeloid metaplasia, a myeloproliferative disorder characterized by clonal hematopoiesis or secondary myelofibrosis which is characterized by polyclonal hematopoiesis. Six exonic X-chromosome polymorphisms were tested to determine the clonality of the patient's platelets and granulocytes (Liu, BLOOD 2003). Unfortunately, this patient was not informative in any of six exonic X-chromosome polymorphism markers, and we could not determine the clonality of hematopoiesis. Peripheral blood CD34 level; however, was low normal, consistent with reactive fibrosis rather than a primary myeloproliferative disease. To our knowledge this is the first report of secondary bone marrow fibrosis in sarcoidosis.