Pericentric X chromosome in a family

Apparent neotelomere in a 46,X,del(X)(qter→p11.2:)/46,X,rea(X)(qter→p11.2::q21.2→qter) novel mosaicism: review of 34 females with a recombinant-like dup(Xq) chromosome

A 26-year-old woman with secondary amenorrhea and turneroid stigmata was found to have a 46,X,rea(X)(qter→p11.2::q21.2→qter)/46,X,del(X)(qter→p11.2:) mosaicism in 101 G-banded metaphases (71 and 30, respectively). The mother's karyotype was normal (the father was already deceased). A fully skewed inactivation of both abnormal X-chromosomes was documented in RBG-banded metaphases and by means of the HUMARA assay. In addition, the latter revealed that the involved X-chromosome was the paternal one. The patient's secondary amenorrhea and turneroid stigmata can reliably be ascribed to her nearly complete Xp deletion present in all cells. Thus, this observation is consistent with the well-known gradation of ovarian function depending on the Xp deletion size. We assume that the first event was an intrachromosome recombination during paternal meiosis between paralogous sequences at Xp11.2 and Xq21.2, which resulted in a fertilizing rea(X) spermatozoid. Early in embryogenesis, the rea(X) dissociated at the Xp11.2 junction point to originate the del(X), which in turn was healed by the de novo addition of telomeric repeats (the acentric Xq21.2→qter segment was lost in the process). The reverse sequence appears unlikely because it implies that the del(X) chromosome was healed only after it undergone a postzygotic interchromatid recombination and apposite segregation required to obtain the rea(X) clone. The present observation further expands the cytogenetic heterogeneity in Turner syndrome and may represent another instance of a terminal deletion healed by the de novo addition of telomeric repeats.

Familial inv(X) (p22q22): ovarian dysgenesis in two sisters with del Xq and fertility in one male carrier

A recombinant chromosome with Xp duplication and Xq deletion was found in two sisters with normal height and gonadal dysgenesis. Their mother and other four relatives, including a fertile male, carried an inv(X) (p22q22); the inverted X was randomly inactivated in one female carrier. The abnormal X chromosome showed inactivation in all the examined cells. This is the tenth report of a recombinant X chromosome. A review of the literature shows that: i) most female carriers of inv(X) are phenotypically normal and fertile; ii) recombinants having short-arm duplication and long-arm deletion are associated with ovarian failure and normal or tall stature, whereas the reciprocal recombinants are compatible with fertility but cause short stature; and iii) except for one index case, all male carriers have a normal phenotype and 11 of them (from eight families) are of proven fertility. Moreover, no instance of male infertility has been documented.

A recombinant X chromosome in a short statured girl resulting from a maternal pericentric inversion

A 7 3/4-year-old girl with short stature was found to have a recombinant (X),dup q chromosome resulting from an apparently unique pericentric inversion (X)(p11.2q26) present in her mother and maternal grandmother. The recombinant X chromosome was shown to be late replicating and the inversion X chromosome to be randomly inactivated. This appears to be only the eighth report (7 female, 1 male) of a recombinant resulting from an X pericentric inversion despite all diagnosed females having mild clinical abnormalities. Reasons for the rarity of such recombinant X chromosomes in man are examined.

X;14 translocation:an exception to the critical region hypothesis on the human X-chromosome

We report on a family in which an X;14 translocation has been identified. A phenotypically normal female, carrier of an apparently balanced X-autosome translocation t(X;14)(q22;q24.3) in all her cells and a small interstitial deletion of band 15q112 in some of her cells had 2 offspring. She represents a fifth case of balanced X-autosome translocation with the break point inside the postulated critical region of Xq(q13 q26) associated with fertility. The break point in this case is located in Xq22, the same band as in four previously published exceptional cases. In most of her cells, the normal X was inactivated. Her daughter, the proposita, has an unbalanced karyotype 46,X,der(X), t(X;14)(q22;q24.3)mat, del(15)(q11.1q11.3)mat. She is mildly retarded and has some Prader-Willi syndrome manifestations. She has two normal 14 chromosomes, der(X), and deletion 15q11.2. Her clinical abnormalities probably could be attributed to the deletions 15q and Xq rather than 14q duplication. In most of cells, der(X) was inactivated. We assume that spreading of inactivation was extended to the 14q segment on the derivative X. Late replication and gene dose studies support this view. Another daughter, who inherited the balanced X;14 translocation and not deletion 15 chromosome, is phenotypically normal.

Pericentric inversions. Problems and significance for clinical genetics

A review is given of the incidence, cytogenetics, and biologic relevance of pericentric inversions (pii). In 251 cases in the literature and our patients, 96 different inversion forms with different breakpoints are found. Eighteen of these cases have been observed several times in unrelated families; they are classified as types. The problem of pii in the heterochromatic regions of chromosomes 1 and 9 is especially emphasized and the investigations required are pointed out. The significance of the individual pii is checked with regard to their behavior in meiosis and their phenotypical relevance. An approximately 1:1 segregation is found. Fertility, stillbirth, and rates of abortion are not statistically altered. The gonadal findings available at present in man are reported and commented on. The occurrence of aneusomic recombinants among the live offspring of carriers shows a marked dependence on the length of the relative inversion segments. Since these are distinctly below average in inversion types, they only result in recombinants in exceptional cases. Certain pointers to an above-random common occurrence of other chromosomal aberrations are not found in families with pii. A correlation between pii and clinical symptoms likewise cannot be detected. However, in this connection it is pointed out that trisomic mosaics were observed jointly with pii(9) and pii(22). The review is completed by a brief examination of the literature concerning the significance of pii in evolution.