In this paper, we report a rare male case with no malformation and a 46,X,+mar (Y), inv(Y) (p11.2;q11.23)? karyotype, in whom the marker chromosome appears by molecular analysis to have been derived from the Y chromosome. The importance of banding studies for precise identification of structurally abnormal chromosomes and the need for chromosome study of family members for the peroper counseling of prenatal diagnosis of such a variant chromosome are discussed. In the presentation of this case, it has been aimed to resolve the socio-psychologic problems at the patients and his/her relatives and to be a guide to doctors about this subject.

Genomic DNA was extracted from peripheral leukocytes collected from a venous blood sample. Genomic DNA was extracted by standard methods from peripheral leukocytes of all patients³. The DNA was amplified for 30 cycles with denaturation at 94ºC for 5 min, at 94ºC for 1 min, at 54ºC 1 min, at 72ºC for 2 min and extension at 72ºC for 6 min using a PTC-100 thermal cycler (MJ Research). The PCR products were separated by electrophoresis on 2 per cent agarose gel containing ethidium bromide and photographed using Gel Doc system (Hero Lab, Germany). Product was obtained 947 bp for Y. Health male and female samples were used as positive and negative control.

A pericentric inversion of chromosome Y was detected in an unborn baby by a second-trimester amniocentesis for prenatal diagnosis because of advanced maternal age. Cytogenetic investigations of the fetal cells revealed a male karyotype with a pericentric inversion of the Y chromosome. Cytogenetic analysis from amniotic fluid cells showed 46,X,+mar (Y) inverted Y (p11.2;q11.23)? (Figure 1). Chromosome analysis of the proband’s father and other elder brother was also undertaken in order to decide whether this inversion was inherited or of de novo origin. The identical pericentric inversion was found in the phenotypically normal proband's father and a elder brother. In this case of familial pericentric inversion, the parents were assured that their unborn baby was anticipated to be normal.

Figure 1: Pericentric inversion of the Y chromosome in this family. Left, diagram showing a normal Y (Y) from a healthy individual and the common inv(Y)(p11.2;q11.23) chromosome [inv(Y)] of the male family members. Right, high resolution G banding of a normal Y (N) and the Y chromosome of case (P).

The existence of Y chromosome was determined by interphase FISH besides a number of metaphase analysis. It was detected SRY gene and centromeric signals in patients with 46,X,+mar(Y), inverted Y(p11.2; q11.23) karyotype (Figure 2). The formation of testes can be considered as existence of SRY (sex-determining region of Y) as a testisdetermining factor. The sequence tagged sites (STS) primers SY14, ZFY, sY84, sY86 (AZFa); sY127, sY134 (AZFb); sY254, sY255 (AZFc) were used for each case. In all cases the SRY gene was present. No mutations were identified in this gene in any of the patients (Figure 3).

Figure 2: The existence of SRY gene was determined by interphase FISH.

Figure 3: Gel photograph showing Y microdeletion. Lane 1, molecular weight marker; lane 2 and 3 negative control (female and male samples), lane 4,5,6,7,8,9,10 and 11: SY14, sY84, ZFY, sY86 (AZFa); sY127, sY134 (AZFb); sY254, sY255 (AZFc).

The amplified loci by PCR in each patient are indicated in the Table 1. The present report illustrates the importance of FISH and molecular techniques as a complement to cytogenetic methods for accurate identification and characterization of chromosome rearrangements in prenatal diagnosis.

Table 1: Amplified loci by PCR in two patients with 46,X,inv(Y)

Prenatal diagnosis has become the major focus of genetic counselling and for this, several important areas of technology have evolved. Especially cytogenetic prenatal diagnosis using analysis of cultured cells from the amniotic fluid at midtrimester was introduced in 1966 by Steele and Breg⁴. Most cases with structural aberrations of sex chromosomes are associated with abnormalities of the external genitalia at birth or lack of secondary sexual characteristics at puberty⁵. The molecular study of individuals with abnormal gonadal differentiation and sex chromosome anomalies has led to the assignment of specific regions for sexual differentiation and gonadal function on the Y chromosome^6-8. Recently, investigation with DNA probes has allowed the generation of a physical deletion map dividing the Y chromosome into eight intervals⁹, and more detailed deletion mapping has been reported¹⁰. Many individuals with sex chromosome abnormalities remain undiagnosed because usually their phenotype falls within the limits of ‘normality,’ although the karyotypic change has an effect on most non-mosaic cases. Even now, when many abnormalities of the sex chromosomes have been defined and their clinical consequences reported in detail, the precise role of the sex chromosomes in sex differentiation and in the genetic control of gametogenesis still remain obscure. FISH is a rapid method for the detection of specific DNA target sequen ces in metaphase and interphase chromosomes. These techniques, combined with conventional G-banding, have a clear diagnostic and prognostic value, and contribute to genetic counselling¹¹.

In 1999, Acar et al were reported conventional and molecular cytogenetic studies in a patient with multiple anomalies who is a carrier of a pericentric inversion on chromosome Y and a chromosome 15p+. His parents were phenotypically normal. The father is a carrier of a pericentric inversion of chromosome Y, and the mother carries a large chromosome 15p+ variant¹².

In our study, the inverted Y was found to be of paternal origin. Maternal chromosomal pattern was normal 46,XX. Cytogenetic investigation of a healthy couple with 2 spontaneous abortions revealed a pericentric inversion of the Y chromosome. In these cases, it was concluded that there was no clinical significance because the same abnormality was found in two other members of the family. All of them have not anormal phenotype. Chromosome analysis of the father is advisable to determine whether or not the inversion is familial in order to be able to provide genetic counselling. This finding suggests that the pericentric inversion of the Y chromosome affects neither the phenotype nor reproductive performance. After reviewing the literature, it was concluded that an inverted Y chromosome does not impede the production of normal sperm and does not predispose to non-disjunction of other chromosomes in the progeny. Thus, the earlier concept of nondisjunction was rejected, and it is suggested that aberrant cases with aneuploidy and an inverted Y are fortuitous. The prevalence of males with pericentric Y inversion in the general population is approximately 1 per 1000. It is suggested that a pericentric inversion of the Y chromosome is a rare chromosomal heteromorphism and should be called type III. The pericentric inverted Y is inherited from generation to generation and has no clinical significance.