American Journal of Medical Genetics 56:22-24 (1995)
Mosaicism for a Chromosome 8-Derived Minute Marker Chromosome in a Patient With Manifestations of Trisomy 8 Mosaicism
Nancy B. Spinner, Kim Rehberg Grace, Nancy L. Owens, Lorraine Sovinsky, Joan E. Pellegrino, Donna McDonald-McGinn, and Elaine Zackai Division of Human Genetics and Molecular Biology, Childrens Hospital of Philadelphia, Philadelphia, Pennsylvania
We describe a patient with manifestations of the mosaic trisomy 8 syndrome and mo- saicism for a minute marker chromosome. Fluorescence in situ hybridization (FISH) with a chromosome 8 probe confirmed that the marker was derived from chromosome 8. This is the smallest piece of chromosome 8 to be reported in a patient with mosaic trisomy 8 syndrome. When the clinical pic- ture is strongly suggestive of trisomy for a specific chromosome region, we believe that FISH can be used to test markers in a guided, rather than random, fashion. 0 1995 Wiley-Liss, Inc.
KEY WORDS marker chromosomes, tri- somy 8 mosaicism, FISH
INTRODUCTION Small supernumerary marker chromosomes are seen
in approximately 0.06% of individuals [Sachs et al., 19877. These markers are heterogeneous, and some are associated with mental retardation and other abnor- malities, while others seem to have no recognizable phenotypic effects [Buckton et al., 19851. Recent ad- vances in molecular cytogenetic techniques have per- mitted identification of the chromosome of origin of many markers which were not identifiable by routine cytogenetic studies alone [Callen et al., 19921. Correla- tions of phenotype and the chromosomal origin of markers now permit identification of markers that carry a high risk for phenotypic abnormality and mark- ers with a low risk.
We have studied a patient with a supernumerary marker chromosome, who presented with a phenotype consistent with the well-defined trisomy 8 mosaic syn-
Received for publication February 8, 1994; revision received October 3, 1994.
Address reprint requests to Nancy Spinner, Ph.D., Division of Human Genetics and Molecular Biology, Childrens Hospital of Philadelphia, Philadelphia, PA 19104.
0 1995 Wiley-Liss, Inc.
drome. Clinical information provided a strong diagnos- tic impression which led to our performing FISH with a specific chromosome probe, bypassing the standard protocol for characterization of marker chromosomes.
CLINICAL REPORT The patient was seen a t age 7 months for skeletal
anomalies and developmental delay. The patient was the 3,579-g (75th centile) product of
a term, uncomplicated pregnancy. Delivery was by ce- sarean section due to breech position. Apgar scores were 8 and 9 at 1 and 10 minutes, respectively. The right kidney was noted to be moderately hydro- nephrotic; however, renal function was within normal limits. The anus was anteriorly placed, and the patient had contractures of the fingers, overlap of toes, and hypoplastic or absent patellae.
At 7 months he was found to have simple ears, camp- todactyly of the third finger at the PIP joint, head cir- cumference and height at the 90th centile, eversion of the lower lip, deep plantar creases, and hypoplastic or absent patellae. In addition, he had ulnar deviation of fingers 3-5 bilaterally, and malalignment of the right foot and a midfoot varus deformity on the left. Analysis of dermatoglyphics documented normal triradii and normal palmar creases. Fingertips demonstrated 4/10 ulnar loops, one radial loop, 2/10 double loops and 3/10 whorls. The remainder of the physical findings were normal. Developmental assessment placed the child at a 6-month level. Radiographic findings showed extra lumbar vertebrae, bifid vertebrae, hypoplasia of the il- iac bones, narrow diaphyses of the long bones, under- developed glenoid fossa, and advanced bone age.
The combination of everted lower lip, deep plantar creases, camptodactyly, possible absent patellae, and the X-ray findings were strongly suggestive of trisomy 8 mosaicism [Riccardi, 19771, and prompted the cytoge- netic analysis described below.
At age 2 years he had a right inguinal hernia repair and correction of the camptodactyly. At 2% years he had normal motor development and normal receptive lan- guage skills, but a significant delay in expressive lan- guage. Follow-up physical examination at age 3 years showed height of 97 cm (75th centile), weight of 12.27
Minute Marker and Trisomy 8 Mosaicism 23
kg (fifth centile), and head circumference of 52 cm (95th centile). The physical exam was unchanged (note everted lip and deep plantar creases, Fig. l), except that his torso was long. Ultrasound examination of the knees demonstrated hypoplastic patellae bilaterally, which are present in the superolateral aspect of the patellar groove. Renal ultrasound demonstrated malro- tated kidneys with thickened extrarenal pelvis. There was a new renal size discrepancy, which was not pre- sent on the prior examination, which is being followed.
CYTOGENETICS AND MOLECULAR CYTOGENETICS
Fifty metaphases from peripheral blood lymphocytes were studied by G-banding, and of these, 22 had an ap- parently normal male karyotype while the remaining 28 had 47 chromosomes including a small supernumer- ary marker. The marker was very small, about the size of an isolated centromere (Fig. 2). Fluorescence in situ hybridization was carried ou&sing a probe for the peri- centromeric (alpha satellite) of chromosome 8. These studies demonstrated that the marker was in
Fig. 2. Photograph of a G-banded metaphase from the patient, demonstrating the small supernumerary marker chromosome (arrow- head). Normal chromosome 8s are indicated with arrows.
fact derived from chromosome 8 (Fig. 3).
A skin biopsy was cultured for further cytogenetic analysis. The culture grew poorly, and only 25 meta- phases could be evaluated. All of these demonstrated a 46,XY apparently normal male karyotype.
Parental lymphocyte chromosomes were studied, and both were found to be normal. There was no evidence for a marker in 100 G-banded metaphase cells studied from each parent. An additional 100 cells from each parent were screened for the presence of the chromo- some 8-derived marker after fluorescence in situ hy- bridization with the chromosome 8 alpha satellite probe. There was no evidence for a low-level mosaicism for the marker.
Fig. 3. Photomicrograph of a metaphase after fluorescent in situ hybridization using a biotin-labeled alpha satellite probe for the peri- centromeric region of chromosome 8. Arrowhead indicates the brightly fluorescent marker chromosome. The two normal 8s (arrows) also give a positive signal.
Fig. 1. Photographs of the patient at age 3 years. A: Facial appearance (note everted lower lip). B Deep plantar creases.
24 Spinner et al.
DISCUSSION Mosaic trisomy 8 is a well-described entity of distinct
facial appearance with everted lower lip and prominent nasal tip, absent or dysplastic patellae, joint contrac- tures, deep plantarlpalmar skin furrows, vertebral de- fects, ureteral and renal anomalies, narrow pelvis, and a distinct toe posture [Riccardi, 19771. We report on a patient with an everted lower lip, hypoplastic ears, a slender trunk, apparently absent patellae, vertebral and other skeletal anomalies, and deep plantar creases. Cytogenetic studies documented mosaicism for a very small marker chromosome, and FISH confirmed that the marker originated from a chromosome 8.
Our patient has the smallest piece of chromosome 8 that has been found to be associated with the mosaic trisomy 8 syndrome. Previous studies have attempted to correlate trisomy for various segments of chromo- some 8 with the manifestations of mosaic trisomy 8, but it has not been possible to make these correlations [Riccardi and Crandall, 1978; Walker and Bocian, 19871. In the summary by Walker and Bocian, absent patellae were seen in 111 patient with dup 8p12+pter, and 4/11 patients with dup 8q22+qter. Plantar or pal- mar furrows were seen in 212 patients with dup 8p12+pter, 113 patients with dup 8p12+p23.3, 111 patients with dup 8pll+pter, 212 patients with dup 8pll+p23.1, 112 patients with dup 8q12+q21.2, and 5/10 patients with dup 8q22-+qter. Findings were sim- ilarly inconclusive for other features of this syndrome.
The marker chromosome in our patient appears to contain a small amount of euchromatin from the peri- centromeric region of 8p, or 8q, or both. The striking similarities in the phenotype of our patient to those of patients with mosaic trisomy 8 suggest an important role for this region of chromosome 8 in the development of the phenotype. No other reports are known to us of marker chromosomes found to be derived from chro- mosome 8. There is a previous report of a patient with mosaic trisomy 8 who had the supernumerary chromo- some in fibroblasts but not in lymphocytes. As cells were subjected to increasing passages in culture, the percentage of trisomic cells decreased, until the 23rd
passage, at which time all cells studied were diploid [Niss and Passarge, 19761. Presumably, the absence of the marker in fibroblasts of our patient is due to a random distribution of this mosaic marker. There is no evidence that mosaicism for trisomy 8 follows a tissue- specific distribution, as has been demonstrated in the Pallister-Killian syndrome [Hunter et al., 19851.
This case demonstrates the importance of combining clinical and cytogenetic information in the application of FISH. With clinical guidance, the cytogenetic labora- tory may be able to circumvent the laborious and ex- pensive task of investigating marker chromosomes. Clinical information can be used to target the use of ap- propriate probes for use in FISH. The identification of marker chromosomes is crucial, beca