American Journal of Medical Genetics 43:722-725 (1992)

Reciprocal Translocation t(1;15)(p36.2;pl1.2): Confirmation of a Suggestive Cytogenetic Diagnosis by In Situ Hybridization and Clinical Case Report on Resulting Monosomy (Ip) Gotthold Barbi, Ingo Kennerknecht, and Christine Klett Abteilung Klinische Genetik der Universitat, Ulm, Germany

A newborn girl with generalized muscular hypotonia and minor anomalies was referred for chromosome analysis. Cytogenetic investigation showed a satellite and an Agpositive NOR on the distal short arm of one chromosome 1,thus indicating an unbalanced translocation involving the short arm of an acrocentric chromosome. The phenotypically normal mother had the same satellited chromosome 1with Agpositive NOR. One chromosome 15 was the only acrocentric chromosome in her karyotype lacking recognizable satellites and an Agpositive NOR. Thus a balanced reciprocal translocation between the short arms of chromosomes 1 and 15 in the mother was suggested. The cytogenetic diag nosis was confirmed by nonradioactive in situ hybridization with the most distal DNA probe on chromosome 1, the probe pl-79, localized at chromosome band 1~36.3.The probe was biotinylated by nick-translation, and detection was done by FITC labelled avidin binding. Hybridization signals were observed on both the mother’s normal chromosome 1and the derivative chromosome 15 but not on her derivative chromosome 1. Consequently, the index patient has an unbalanced karyotype with monosomy (11336.3). Comparing their clinical reports shows that patients with similar terminal deletions of l p share several manifestations. o 1992 Wiley-Liss, Inc.

KEY WORDS: reciprocal translocation, monosomy (1p36.3), in situ hybridization

INTRODUCTION Several chromosome regions in the human karyotype are known to be polymorphic. In clinical cytogenetics the detection of an unusual morphology of such a variable chromosome region leads to the application of multiple cytogenetic techniques to distinguish between a chromosome aberration with phenotypic consequences, or a mere variant. We demonstrate the usefulness of nonradioactive fluorescent in situ hybridization (FISH) in diagnostic clinical cytogenetics in the case of a reciprocal translocation, where the unbalanced form in the index patient and the balanced form in the mother could hardly be differentiated by classical cytogenetics. CLINICAL REPORT K.B. is the first child of nonconsanguineous parents. After an uneventful pregnancy a girl was born in the 41st week of gestation (birthweight 2,200 g, length 46 cm, OFC 33 cm). There were no signs of perinatal asphyxia (Apgar score 9/10/10). Besides a generalized muscular hypotonia several minor anomalies were noted (Fig. 1): prominent forehead, broad nasal bridge, upslanting eyes, “dysplastic,” apparently low-set ears, cleft soft palate, cleft uvula, hydrocephalus internus e vacuo, and dysplasia of the hip joints. Toes were clenched, and the 2nd and the 4th toes overlapped the 3rd toe; the 5th toe showed clinodactyly on both sides. At age 12 months, the girl was severely psychomotorically retarded. The somatic data were between the 3rd and 10th centile (weight 8,150 g, length 69,4 cm, OFC 44 cm). At 15 months, sensomotoric dysfunction was diagnosed. Audiometric examinations confirmed a left-sided nerve deafness. Fixation was complicated by a rotatory nystagmus and convergent strabismus. The pupils were fixed. The optics discs were pale and the fundi depigmented. Together with the ERG findings a retinal dysfunction was assumed.

MATERIALS AND METHODS Lymphocytes were cultivated in medium RPMI 1640; Received May 31, 1991; revision received September 23, 1991. Address correspondence to G. Barbi, Abteilung Klinische chromosomes were prepared by standard techniques Genetik der Universitat, Frauenstr.29, W-7900 Ulm, Germany. and sequentially stained by QFQ-banding and by silver

0 1992 Wiley-Liss, Inc.

Reciprocal 'Ikanslocation t(1;15)(p36.2;p11.2)

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Fig. 1. The index patient at 16 months.

1.

13

14

16

21

22

Fig. 2. Partial karyotype of satellited chromosomes in the index patient (1st and 2nd row) and her mother (3rd and 4th row) after Q-banding (1st and 3rd row) and silver staining of NORs (2nd and 4th row). The satellited chromosome 1 is indicated by a black triangle, the derivative chromosome 15 in the mother by a white triangle.

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Barbi et al.

staining of NOR according to the procedure of Howell and Black [19801 to allow for the characterization of previously identified chromosomes. For nonradioactive in situ hybridization a 900 bp DNA probe, pl-79 [Buroker et al., 19871,the most distal probe of chromosome 1,localized at locus D1Z2 in chromosome band 1p36.3 [Dracopoli et al., 19911,was used. In situ hybridization was done essentially as described by Cherifet al. [19891. The DNA probe was labelled with biotinylated 11-dCTP (BRL) by nick-translation. For probe detection FITC-avidin was used. Staining was done with propidium jodide as described.

RESULTS AND DISCUSSION Chromosome analysis of the index patient after routine QFQ-banding showed a structurally altered chromosome 1 bearing a small satellite with bright QFQ-fluorescence on its distal short arm (Fig. 2, upper row) indicating a translocation involving the short arm of an acrocentric chromosome-a chromosome region known to be highly polymorpic [ISCN, 19851. By silver staining up to 11 Ag-positive NORs per cell could be demonstrated, namely on each of the acrocentric chromosomes (No. 13-15, and No. 21-22) as well as on the derivative chromosome 1 (Fig. 2, second row). The mother had the same der(1) (Fig. 2, third row). Silver staining of her metaphases showed a maximum of 10 Ag-positive NORs with one Ag-negative chromosome 15 in each cell investigated (Fig. 2, lower row). All 4 homologous chromosomes 15 of her parents had Ag-positive

NORs. Since Ag-stainability of NORs is regarded as a heritable property of individual chromosomes [Marcovic et al., 19781, a balanced reciprocal translocation t(1;15)(p36;p11.2)in the mother leading to a unbalanced offspring was the most plausible interpretation. However, silver staining of an NOR is rather correlated with its activity than with its mere presence [de Capoa et al., 19881,and variability of active NORs has been described between generations [Jotterand-Bellomo and van Melle, 19811. Hence, confirmation of the suggestive cytogenetic diagnosis of a balanced reciprocal translocation was sought by FISH. As shown in Figure 3, the DNA probe pl-79, localized a t chromosome band 1~36.3,is present on both short arms of the mother’snormal chromosome 1 and of one chromosome 15 but not on the derivative homologue of chromosome 1.Thus the interpretation of a balanced reciprocal translocation could be confirmed. The index patient has an unbalanced karyotype as the consequence of maternal co-segregation of the derivative chromosome 1 and the normal chromosome 15. Hence, the phenotype of the child can be attributed to monosomy (1~36.3). Furthermore, easy discrimination between the balanced and unbalanced forms of the translocation is possible, thus facilitating genetic counselling. When the clinical reports of propositi with a comparable terminal deletion of chromosome l p are evaluated, similar manifestations are evident (Table 1).However, a deletion syndrome of del(l)(p36) cannot be properly de-

Fig. 3. In situ hybridization with chromosome 1-specific DNA probe pl-79 in a metaphase of the mother. Hybridization signals are visible on the normal chromosome 1 (thin arrowhead) and on the derivative chromosome 15 (thick arrowhead).

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Reciprocal Tkanslocation t(1;15)(~36.2;~11.2) and cage report on monosomy (lp) TABLE 1. Manifestations of Patients With del(lM~36) Reference phenotype Growth retardation Psychomotor retardation Seizures Muscle tonus Asymmetric skull Frontal bossing Occiput Wide fontanelle Eyes

Hain et al. [1980] Patient 1" Patient 2"

Yunis et al. [I9811

Steele et al. [19841

Abbas et al. [19901

+

t + Prominent

Ears Prominent

Nasal bridge Cleft palate

(+I

+

+

t

1

(1)

+

+

+

+

Flat

Flat

+

.1

Deep-set amaurotic Low-set

Deep-set

Deep-set

Large

Depressed

Prominent

Low-set large Flat, wide

+

& Lip

Heart

Cardiomegaly

Cardiomegaly

+

Clinodactyly

Our patient

lnfundibular stenosis

+

and Camptodactyly

+

+ 1

+ + +

Deep-set amaurotic Low-set Wide

+

+

Toes

"Patient also had d e l ( l 5 ) ( p t e ~ q l l ) .

KH, Nishimura DY, Murray JC, Helms C, Mishra SK, Donis-Keller lineated. This is mostly due to differently detailed docuH, Hall JM, Lee MK, King M-C, Attwood J , Morton NE, Robson EB, mentation. Among the common findings, psychomotor Mahtani M, Willard HF, Royle NJ, Pate1 I, Jeffreys AJ, Verga V, retardation, muscular hypotonia, low-set ears, deep-set Jenkins T, Weber JL, Mitchell AL, Bale AE (1991): The CEPH Consortium linkage map of human chromosome 1. Genomics and amaurotic eyes are the most specific. The other spe9:686-700. cific finding, cardiomegaly, was only found in 2 unreD, Leversha M, Campbell N, Daniel A, Barr PA, Rogers J G (1980): lated patients, who in addition suffer from monosomy Hain The ascertainment and implications of an unbalanced translocation (15)(ptewqll). It is noteworthy that only in the case in the neonate. Familial 1;15translocation. Aust Paediat J 16:196reported by Steele et al. [19841 a terminal deletion of 200. chromosome l p has been shown by classical cytogene- Howell WM, Black DA (1980): Controlled silver-staining of nucleolus organizer regions with a protective colloidal developer: A 1-step tics.

REFERENCES Abbas N, Novelli G, Stella NC, Triolo 0,Corrado F, Fellous M, Chery M, Gilgenkrantz S, Dallapiccola B (1990): A 45,X male with molecular evidence of a translocation of Y euchromatin onto chromosome 1. Hum Genet 86:94-98. Buroker N, Bestwick R, Haight G , Magenis RE, Litt M (1987): A hypervariable repeated sequence on human chromosome lp36. Hum Genet 77:175-181. Cherif D, Bernard 0,Berger R (1989):Detection of single-copy genes by nonisotopic in situ hybridization on human chromosomes. Hum Genet 81:358-362. de Capoa A, Felli MP, Baldini A, Rocchi M, Archidiacono N, Aleixandre C, Miller OJ,Miller DA (1988): Relationship between the number and function of human ribosomal genes. Hum Genet 79301-304. Dracopoli NC, O'Connell P, Elsner TI, Lalouel J-M, White RL, Buetow

method. Experientia 361014. ISCN (1985): "An International System for Human Cytogenetic Nomenclature." Harnden DG, Klinger HP, Jensen JT, Kaelbling M (eds), published in collaboration with Cytogenet Cell Genet. Basel: Karger. Jotterand-Bellomo M, van Melle G (1981): Variability of the nucleus organizer activity in human lymphocytes via Ag-staining. Hum Genet 59:141-147. Marcovic VD, Worton RG, Berg JM (1978):Evidence for the inheritance of silver stained nucleolus organizer regions. Hum Genet 41:181187. Steele MW, Wenger SL, Geweke LO, Golden WL (1984): The level of 6-phosphogluconate dehydrogenase (6-PGD) activity in a patient with a l p terminal deletion suggests that the gene locus is not distal to sub-band p36.3 on chromosome 1.Clin Genet 2559-62. Yunis E, Quintero L. Leibovici M (1981):Monosomy lpter. Hum Genet 56:279-282.