Familial transmission of a deletion of chromosome 21 derived from a translocation between chromosome 21 and an inverted chromosome 22

Double deletion of a chromosome 21 inserted in a chromosome 22 in an azoospermic patient

We report on a phenotypically normal 41-year-old azoospermic man with a 45 chromosomes karyotype including one normal chromosome 21, one normal chromosome 22, and a der(22)ins(22;21). Array CGH showed a 1.8 Mb terminal deletion of bands 21pter to 21q21.1 and a 341 kb terminal deletion on band 21q22.3.

Inherited 14q duplication and 21q deletion: a rare adjacent-2 segregation in multiple family members

We present a family with multiple carriers of a subtle balanced translocation t(14;21)(q21.2;q21.2) and three patients with a resultant adjacent-2 malsegregation containing a +der(14)t(14;21)(q21.2;q21.2),-21 in their chromosome complement. The initial study was performed when a 2-month-old female was referred to genetics clinic for evaluation of developmental delay, growth retardation, and failure to thrive. Physical findings included prominent eyes, micrognathia, prominent and simple external ears, camptodactyly, contractures of the wrists, ankles, and hips, hypoplasia of the corpus callosum, prominent atria and occipital horns, cerebellopontine hypoplasia; and small atrial septal defect. High resolution chromosomes showed an extra band on the proximal 21q and fluorescence in situ hybridization (FISH) demonstrated only one signal for the centromere of 21. Karyotypes of the parents and grandparents revealed that the mother and maternal grandfather were carriers of a balanced translocation, and the propositus contained an unbalanced chromosome complement with partial duplication of proximal 14q and partial deletion of proximal 21q. Investigations performed on an institutionalized maternal aunt revealed identical karyotypic abnormalities as in the propositus. More recently, array comparative genomic hybridization (aCGH) on a subsequent child with multiple congenital anomalies further out in the extended family allowed for more accurate identification of the breakpoints. Our investigation includes analysis on a total of 11 family members spanning three generations. Among those investigated, there were no living members with other possible consequential unbalanced translocations or with adjacent-2 segregation resulting in -14,+der(21). Chromosome rearrangements require FISH and aCGH studies for accurate identification and elucidation of the abnormality and breakpoints.

Consistent chromosome abnormalities identify novel polymicrogyria loci in 1p36.3, 2p16.1-p23.1, 4q21.21-q22.1, 6q26-q27, and 21q2

Polymicrogyria is a malformation of cortical development characterized by loss of the normal gyral pattern, which is replaced by many small and infolded gyri separated by shallow, partly fused sulci, and loss of middle cortical layers. The pathogenesis is unknown, yet emerging data supports the existence of several loci in the human genome. We report on the clinical and brain imaging features, and results of cytogenetic and molecular genetic studies in 29 patients with polymicrogyria associated with structural chromosome rearrangements. Our data map new polymicrogyria loci in chromosomes 1p36.3, 2p16.1-p23, 4q21.21-q22.1, 6q26-q27, and 21q21.3-q22.1, and possible loci in 1q44 and 18p as well. Most and possibly all of these loci demonstrate incomplete penetrance and variable expressivity. We anticipate that these data will serve as the basis for ongoing efforts to identify the causal genes located in these regions.

Array-based genomic delineation of a familial duplication 11q14.1-q22.1 associated with recurrent depression

Detection of abnormal karyotypes with associated clinical manifestations is an important tool for the identification of genes that confer susceptibility to genetic disorders. We present a family with a duplication 11q14.1-q22.1 resulting from an unbalanced familial insertion, associated with a mild dysmorphic phenotype and mood disorders, mainly major depression. This relatively large duplication of a segment from chromosome 11 is associated with a surprisingly little physical phenotypic effect in this family. The finding of mood disorders in adult members of the family who carry the insertion supports the view that the duplication may be important for the identification of contributing gene(s) to mood disorders. Major depression is considered to be a complex trait with multiple genetic alterations interacting with environmental factors. Array-based comparative genome hybridization (array CGH) analysis with a 1 Mb genomic array, defined the duplication region that extended over 16 Mb from 11q14.1 to 11q22.1. Brain-expressed genes that map within this 16 Mb region, are considered worthy of further investigation as gene(s) contributing to the etiology of major depression.

Tertiary trisomy due to a reciprocal translocation of chromosomes 5 and 21 in a four-generation family

Tertiary trisomy, or double trisomy, is a rare occurrence. We present two individuals with a previously unreported tertiary trisomy for chromosomes 5p and 21q in an eight-generation pedigree. Their phenotypes are compared with other partial trisomies of either 5p or 21q from the literature. The propositus was diagnosed with trisomy 21 at 2 years of age after a karyotype study for short stature and developmental delay. His phenotype was described as atypical for Down syndrome. He presented at 9 years of age because of pervasive behavioral problems and obesity. He was brachycephalic with a flattened nasal bridge, but he lacked other characteristics of trisomy 21. Because of lack of phenotypic evidence of Down syndrome, a repeat karyotype was obtained and showed 47,XY, +der(21)t(5;21)(p15.1; q22.1), incorporating partial trisomies of both chromosomes 5 and 21. Mother had a balanced translocation, 46, XX,t(5;21)(p15.1; q22.1); 8 other relatives were examined. The translocation originated from the maternal great-grandmother, but only the propositus and his mentally retarded aunt had a similar phenotye and the derivative chromosome. Fluorescence in situ hybridization showed absence of band 21q22.2 in the derivative chromosome of the propositus and his aunt, indicating that neither had trisomy for the Down syndrome critical region. These cases represent a unique double partial trisomy of chromosome arms 5p and 21q that occurred because of 3:1 malsegregation of a reciprocal translocation. These cases further demonstrate that phenotypic discordance with cytogenetic results dictate further investigation using advanced cytogenetic hybridization.