**3. Results**

Fourteen patients were included in the study (Table 1). There were 7 boys and 7 girls. The median age at the time of cytogenetic exam was 7.5 months. Except for a patient who was almost 10 years old, all the other patients were less than 3 years old at the time of cytogenetic analyses, the majority of them being less than 1 year old (9 of 14 patients).

Cardiovascular anomalies and facial dysmorphism were present in all patients, but for one without cardiovascular anomaly and another without dysmorphism (Table 1). Growth and psychomotor retardation was noted in all patients. Stellate irides and/or strabismus was also present in 7 of the 12 patients for whom the data was available. No cognitive nor personality profile was available for the patients, mainly due to their young age.

R-banding conventional cytogenetics showed a normal 46,XY or 46,XX karyotype whereas FISH using the Vysis Williams Region Probe revealed a deletion of the *ELN*, *LIMK1* and D7S613 locus in all 14 patients (Figure 1-A).

Fig. 1. Example of FISH results in a patient with Williams-Beuren syndrome. (A) FISH using the commercially available probe (ELN in SpectrumOrange and D7S486, D7S522 in SpectrumGreen). (B) FISH using two BAC clones (RP11-614D7 in green and RP11-1105J19 in red).

Sequential FISH analyses with BAC clones were applied on metaphases of all 14 patients having a deletion of the Vysis Williams Region Probe (Figure 1-B). They showed the centromeric deletion boundary to be located in a 145 kb interval, between RP11-598B14, deleted in 13 patients (P1 to P13), and RP11-48D17, always present (Figure 2). The telomeric deletion boundary was found to be located in a 229 kb interval, between RP11-351B3, deleted in 13 patients (P1 to P13), and RP11-1105J19, always present. Therefore, the minimum and maximum estimated deletion sizes for these 13 patients (P1 to P13) were 1,048,937 bp and 1,423,771 bp, respectively. Using overlapping BAC clones, both centromeric and telomeric boundaries could be refined. FISH signals with BAC clones RP11- 614D7 and RP11-101D2, located at the centromeric deletion boundary, and those RP11-

Fourteen patients were included in the study (Table 1). There were 7 boys and 7 girls. The median age at the time of cytogenetic exam was 7.5 months. Except for a patient who was almost 10 years old, all the other patients were less than 3 years old at the time of cytogenetic analyses, the majority of them being less than 1 year old (9 of 14 patients).

Cardiovascular anomalies and facial dysmorphism were present in all patients, but for one without cardiovascular anomaly and another without dysmorphism (Table 1). Growth and psychomotor retardation was noted in all patients. Stellate irides and/or strabismus was also present in 7 of the 12 patients for whom the data was available. No cognitive nor

R-banding conventional cytogenetics showed a normal 46,XY or 46,XX karyotype whereas FISH using the Vysis Williams Region Probe revealed a deletion of the *ELN*, *LIMK1* and

(a) (b)

Fig. 1. Example of FISH results in a patient with Williams-Beuren syndrome. (A) FISH using

SpectrumGreen). (B) FISH using two BAC clones (RP11-614D7 in green and RP11-1105J19 in

Sequential FISH analyses with BAC clones were applied on metaphases of all 14 patients having a deletion of the Vysis Williams Region Probe (Figure 1-B). They showed the centromeric deletion boundary to be located in a 145 kb interval, between RP11-598B14, deleted in 13 patients (P1 to P13), and RP11-48D17, always present (Figure 2). The telomeric deletion boundary was found to be located in a 229 kb interval, between RP11-351B3, deleted in 13 patients (P1 to P13), and RP11-1105J19, always present. Therefore, the minimum and maximum estimated deletion sizes for these 13 patients (P1 to P13) were 1,048,937 bp and 1,423,771 bp, respectively. Using overlapping BAC clones, both centromeric and telomeric boundaries could be refined. FISH signals with BAC clones RP11- 614D7 and RP11-101D2, located at the centromeric deletion boundary, and those RP11-

the commercially available probe (ELN in SpectrumOrange and D7S486, D7S522 in

personality profile was available for the patients, mainly due to their young age.

D7S613 locus in all 14 patients (Figure 1-A).

**3. Results** 

red).

247L6 and RP11-137E8, located at the telomeric deletion boundary, showed decreased intensities. The centromeric and telomeric intervals were reduced to 36 kb and 93 kb, respectively, giving an estimated WBS deletion size of 1.17Mb.

Fig. 2. Size of the deletions in the 14 WBS patients estimated by BAC clones (ELN: elastin gene)

The fourteenth patient (P14) was found to have a centromeric deletion boundary to be located in a 109 kb interval, between RP11-101D2 (deleted) and RP11-48D17 (present). Using overlapping BAC clones RP11-483G21 and RP11-614D7, the centromeric boundary was refined to a 77 kb interval. The telomeric deletion boundary was found to be located at the junction of two overlapping BAC clones (RP11-926D5 and RP11-1105J19). Therefore, the estimated WBS deletion size for this patient was 1.41Mb.
