Deletion of 22q11 in Two Brothers WithDifferent Phenotype

Lidia Kasprzak,1,5 Vazken M. Der Kaloustian,1,5* Alison M. Elliott,1,5 Michael Shevell,1,3,5

Christine Lejtenyi,4 and Patrice Eydoux2

1The F. Clarke Fraser Clinical Genetics Unit and Division of Medical Genetics, Montreal Children’s Hospital,Montreal, Quebec, Canada

2Departments of Pathology, Pediatrics and Human Genetics, McGill University, Montreal, Quebec, Canada3Division of Neurology, McGill University, Montreal, Quebec, Canada4Division of Allergy and Clinical Immunology, McGill University, Montreal, Quebec, Canada5Department of Human Genetics, McGill University, Montreal, Quebec, Canada

We have studied two brothers with submi-croscopic 22q11 deletion. One brother hadfindings suggestive of DiGeorge syndrome,while the other had milder anomalies, in-cluding polydactyly. Fluorescence in situhybridization (FISH) showed a minor cellline with deletion 22q11 in the mother. Toour knowledge, this is the first report of adeletion of 22q11 in two sibs with differentphenotypes and apparent maternal mosa-icism detected with FISH. This family illus-trates the variability of the syndrome andfurther demonstrates the possibility of go-nadal mosaicism for a microdeletion. Prena-tal diagnosis may be offered after the birthof a child with a 22q11 deletion, even in theabsence of parental chromosomal anoma-lies. Am. J. Med. Genet. 75:288–291, 1998.© 1998 Wiley-Liss, Inc.

KEY WORDS: DiGeorge syndrome; micro-deletion; 22q11; gonadal mo-saicism; prenatal diagnosis

INTRODUCTION

The DiGeorge anomaly is heterogeneous [Lammerand Opitz, 1986]; microscopic or submicroscopic dele-tions of 22q11.2 are the cause of most cases of DiGeorgesyndrome (DGS) [Driscoll et al., 1992]. Here, we de-scribe two brothers with a submicroscopic deletion of22q11 identified with fluorescence in situ hybridization(FISH).

CLINICAL REPORTS

The two brothers, 6½ and 5 years old, were born tononconsanguineous, phenotypically normal Caucasianparents.

J.H. was born to his G4P2A1 mother at 39 weeks ofgestation, after an uneventful pregnancy. Birth weightwas 3,050 g (25th centile), length 49.5 cm (25th cen-tile), and occipito-frontal circumference (OFC) 33 cm(10th centile). Apgar scores were 7 and 8 at 1 and 5minutes, respectively.

He had bilateral epicanthic folds, relatively largeand apparently low-set ears, a small mouth, mild mi-crognathia and a high, narrow-arched palate (Fig.1a,b). An accessory digit on the right fifth finger wasremoved in infancy. He had lax joints, bilateral genuvalgum, and a congenital subluxation of the right pa-tella.

His growth fell below the 5th centile. At 6 years, hisbone age was 4 years. At 5 years he had mild globaldevelopmental delay. The child had frequent ear andupper respiratory tract infections. Immunological stud-ies did not show any significant abnormalities, otherthan a slightly low number of T-suppressor cells (17 ×106/ml, age-adjusted normal range: 19–48 × 106/ml).There was no evidence of cardiac malformation. Totalserum calcium was normal.

P.H. was born at 383⁄7 weeks of gestation. His birthweight was 3,430 g (50th centile) and OFC 34 cm (25thcentile). Borderline gestational diabetes mellitus wasnoted during this otherwise uneventful pregnancy. Atbirth, Apgar scores were 8 and 9 at 1 and 5 minutes,respectively.

He had slightly low-set ears, prominent nasal bridge,everted lower lip, small mouth, mild micrognathia,high and narrow-arched palate (Fig. 2a,b). An umbili-cal hernia was noted at birth. He had generalized hy-potonia and, at age 3, he was hyperactive, had speechdelay, and a poor attention span. His development wasslightly delayed. EMG was normal.

A small atrial septal defect, ventricular septal defect,stenotic, bicuspid aortic valve, patent ductus arterio-

*Correspondence to: Vazken M. Der Kaloustian, The F. ClarkeFraser Clinical Genetics Unit, Montreal Children’s Hospital,2300 Tupper Street, Montreal, Quebec, Canada. E-mail:MDDK@musica.mcgill.ca.

Received 28 March 1997; Accepted 9 May 1997

American Journal of Medical Genetics 75:288–291 (1998)

© 1998 Wiley-Liss, Inc.

sus, and interrupted aortic arch were detected throughclinical and ultrasound examinations. Surgery wasperformed at 5 days to correct the cardiac defects, andalso demonstrated a small thymus. No recurrent infec-tions were noted. Lymphocyte analysis showed an in-creased number of B cells, low T-suppressor cells, andan increased CD4-CD8 ratio (Table I). Serum immuno-globulin levels and in vitro lymphocyte mitogen respon-siveness were normal. Neonatal hypocalcemia was de-tected with a serum calcium concentration of 1.74 mM(normal range 2.2–2.76). It resolved after initial cal-cium supplementation.

The diagnosis of DiGeorge syndrome was made, andlater confirmed by molecular cytogenetic studies.

CYTOGENETIC INVESTIGATIONS

Banded prometaphase GTG karyotypes (550 bands)did not show any deletion. Fluorescence in situ hybrid-ization (FISH) was performed using a probe recogniz-ing D22S75, within the DiGeorge critical region,(DGSCR) at 22q11.2, along with a distal control probeat locus D22S39 (Oncor®, Gaithersburg, MD). The hy-bridization experiments were performed according tothe instructions of the manufacturer. The FISH signalwas visualized together with the banding, using a tech-nique reported elsewhere [Zhang et al., 1994]. Only the

chromosomes with a signal in the D22S39 control re-gion were scored under a Zeiss fluorescence micro-scope. In all cells of both patients, only one signal wasseen at the DGSCR (Fig. 3).

Fifty-one cells were analyzed by FISH in the father;no deletion was noted. In the mother, a deletion wasseen in eight cells of 115 (7.0%). This number is sig-nificantly greater than in controls (2.3%: seven dele-tions in 301 cells, x2 test with Yates correction, P <0.05).

DISCUSSION

Both of our patients have a microdeletion of 22q11,and were born to normal parents. The younger patientwas diagnosed with DGS; the older patient presentedwith nonspecific signs and a milder presentation of thiscondition. He did not have cardiac anomalies and se-rum calcium level was normal. He had polydactylywhich was reported previously in DGS [Cormier-Daireet al., 1995].

From the reports of cytogenetic abnormalities foundin association with this condition, it is clear that 22q11deletion may be associated with extremely mild pheno-types. The least severely affected patients had only mi-nor facial anomalies and some developmental delay[Lipson et al., 1994; Lindsay et al., 1995]. In the pres-

Fig. 1. a: Patient J.H., face. b: Patient J.H., profile.

Deletion of 22q11 in Siblings 289

ent report, the older brother was not diagnosed clini-cally as having DGS until the confirmation of the di-agnosis by FISH studies in his younger brother, whichwarranted similar studies in him. The classical dele-tion at 22q11.2 was found in both children, in all cells.

FISH studies demonstrated a deletion in 7% of themother’s lymphocytes, indicating apparent mosaicism.The maternal origin of our cases is also consistent witha higher frequency of maternal inheritance of familialcases of DiGeorge syndrome already published[Desmaze et al., 1993; Demczuk et al., 1995]. Recur-rence of DiGeorge syndrome is well known in caseswith a parental deletion [Wilson et al., 1993], and hasalso been documented using molecular techniques[Sitch et al., 1996].

These two patients illustrate the variable phenotypicexpression of the same microcytogenetic abnormality

[Greenberg, 1993; Leana-Cox et al., 1996; Wilson et al.,1992]. No clear correlation between the extent of thedeletion and the phenotype has been demonstrated[Demczuk et al., 1994; Lindsay et al., 1995]. There isalso no clear explanation for the discordant phenotypes

Fig. 3. Deletion at 22q11.2 in patient J.H. visualized by fluorescence insitu hybridization (FISH). Arrows, DiGeorge critical region (Oncor®).

TABLE I. Lymphocyte Markers in Patient P.H.

Lymphocyte markers Cell count (%) Normal range (%)

Total T (CD 3) 41 60–85Total B (CD 19) 38 7–23T helper (CD 4) 37 29–59T suppressor (CD 8) 8 19–48CD 4/CD 8 ratio 4.6 0.6–2.8

Fig. 2. a: Patient P.H., face. b: Patient P.H., profile.

290 Kasprzak et al.

in patients with the same chromosome anomaly. Thisvariability has even been reported in monozygotictwins with different phenotypes. Both had findingsconsistent with DGS, but only one had a cardiac mal-formation [Goodship et al., 1995]. Thus, an effect ofmodifier alleles at the same or different loci, or theeffect of a recessive gene at the DiGeorge critical regiondo not account for all the variability; rather, we wouldseem to be dealing with the epigenetic nature of devel-opment.

To our knowledge, this report is the first instance ofapparent germline mosaicism for a microdeletion syn-drome. We suggest that patients with mild mental re-tardation and palate anomalies (ranging from cleft pal-ate to velo-pharyngeal incompetence) should haveFISH studies to rule out a 22q11 deletion.

The confirmation of mosaicism is important for ge-netic counselling and prenatal diagnosis. Thus, everycase of DGS with a documented deletion should prompta FISH study of the parents. Even though the recur-rence risk is low for sibs of DGS patients whose parentsare phenotypically normal, this report indicates that anormal parental routine FISH study may not rule out apossible recurrence. Ultrasonographic and cytogeneticprenatal diagnosis may be offered for subsequent preg-nancies.

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