جستجوی مقالات مرتبط با کلیدواژه "جابه جایی کروموزومی" در نشریات گروه "پزشکی"

Mental retardation is defined as impaired mental capacity and ability to comply with environmental and social conditions. Chromosomal abnormalities are the most important causes of mental retardation. Carriers of balanced chromosomal translocation are phenotypically normal, although they may be at risk of infertility, recurrent miscarriage or giving birth to mentally retarded children. These abnormalities are caused because chromosomes participated in the reciprocal translocations produce quadrivalents at meiosis. These quadrivalents segregate and lead to several different meiotic outcomes, just two of which are normal or balanced.
A consanguineous family with three mentally retarded daughters at the ages of 24, 18 and 10 years was referred to Comprehensive Medical Genetics Centre, Shiraz, Iran in 2015. Family history showed a case of unexplained infant death as well as a spontaneous abortion. Three survived siblings had hypotonia and severe developmental delay during infantile period. In addition, they suffer from primary amenorrhea. Two siblings have vesicoureteral reflux (VUR). Cytogenetic analysis of two patients showed 46,XX,t(6;12)(q23;q22),der(9)t(8;9)(q24;p24) with partial monosomy of chromosome 9 and partial trisomy of 8q24 segment, while the other patient had 46,XX,der(12)t(6;12)(q23;q22) with partial monosomy of 12q22qter and partial trisomy of 6q23qter segment. Their mother had two balanced chromosomal translocations (46, XX, t(6,12)(q21;q22), t(8,9)(q24;p24)).
The above presented case is another example for the rare occurrence of double balanced chromosomal translocations in a phenotypically normal person. Although the most important causes of mental retardation in consanguineous marriages are autosomal recessive disorders, the role of chromosomal aberrations in mental retardation in these families must not be neglected. In other words, cytogenetic studies should be performed as a first line test in either situation.

A 29 years old girl with various dimorphic features including short stature and webbed neck with mild to moderate mental retardation was referred to our center for chromosome investigation. Her parents were first cousins. The mother has had two previous miscarriages, one deceased son (12 years old) with apparently similar abnormal features to the proband with congenital heart problems, and one normal son (27 years old). The patient, her mother and the brother, all were found to have an apparently balanced reciprocal translocation between the long arms of chromosomes 4 and 10. The breakpoint on chromosome 4 is at the distal end (4q35), while for chromosome 10, it is proximal to the centromere (10q11.2). FISH studies using multiprobe subtelomeric specific probes as well as whole chromosome paints for chromosomes 4 and 10 were carried out in search of a genetic imbalance. The FISH results revealed no telomeric rearrangements and confirmed the balanced reciprocal translocation between chromosomes 4 and 10. To date, this is the first reported case of t(410)(q35q11.2).

Chromosomal aberrations are one of the causes of infertility. The major chromosomal abnormalities are usually associated with somatic abnormalities. There are also some balanced chromosomal aberrations, without somatic abnormalities however producing unbalanced gametes which result in infertility. The most common of these are balanced translocation. Among 47350 karyotypes performed in our center. There are 664 (1.4%) chromosomal translocation 47 (7%), which are associated with infertility. The sex, and chromosomal aberrations of these cases presented in this paper.