Partial duplication of chromosome 20 ( pter → q 12 )

Partial duplication of chromosome 20 (20pter®20q12) resulting from a maternally inherited translocation t(14;20)(q11;q13) is described in a female child with neuropsychomotor retardation and multiple congenital anomalies. To our knowledge this is the largest duplication of chromosome 20 that includes segments of both the short and the long arms thus far described in a live-born child.


INTRODUCTION
Numerical and structural abnormalities involving chromosome 20 are extremely rare in live-born babies.Most cases of partial duplications involve the short arm and just a few affect the long arm (Sanchez et al., 1977;Pawlowitzki et al., 1979;Sax et al., 1986).Some partial duplications of chromosome 20 showed involvement of the entire short arm and part of the long arm, associated with small duplications or deletions of other autosomal segments (Krmpotic et al., 1971;Marcus et al., 1979;Rudd et al., 1979;Schinzel, 1980;Delicado et al., 1981).
We describe a girl with partial duplication of chromosome 20 (20pter→20q12) which resulted from a maternally inherited translocation t(14;20)(q11;q13).To our knowledge, this is the largest partial duplication of chromosome 20 described hereto.

CLINICAL REPORT
The patient (Figure 1), a black female child, is the first daughter of healthy, unrelated parents, the mother and father being 23 and 25 years old, respectively, at her birth.The mother's second pregnancy resulted in a spontaneous abortion after two months of gestation.The girl was born post-term by cesarean section, after an uneventful pregnancy.At birth, weight was 2,450 g and length, 44.5 cm.Her health was good, but she was noted to be hypotonic.Motor development was delayed: she held up her head at 5 months of age and sitting without support occurred only at 10 months.
At 3 years and 6 months of age, the patient presented psychomotor retardation; she could not stand up or walk; there was no speech development and generalized hypotonia was observed.Her height was 77 cm (below the 3rd centile) and weight, 12 kg (3rd centile).She had a round face and a narrow forehead.The frontal bones presented a prominent metopic suture and lateral depressions.Facial dysmorphisms included a mongoloid slant of palpebral fissures, apparent hypotelorism, bilateral convergent strabismus, a depressed broad nasal bridge, a short nose with upturned tip and large nares, a long philtrum, a thin upper lip, and retrognathia.She had a highly arched palate.The ears were short, low set and posteriorly angulated, with overfolding of the helices.The neck was short, and the abdomen appeared normal except for an umbilical hernia.The distal phalanges of digits and toes, especially of the thumbs and halluces, were broad.The hands showed single palmar flexion creases.Pes planus and a prominent calcaneum were observed bilaterally.Radiological examination documented thoracic kyphosis.An electroencephalogram at 3 years of age did not reveal any abnormalities.
At 6 years and 9 months of age, the patient was a healthy girl with severe neuropsychomotor retardation.She sat down without support, but could not stand up or speak.Comprehension of simple orders was rather poor, irritability was constant and sphincter control had not developed.Her height was 92.5 cm (below the 3rd centile) and the head circumference, 47.5 cm (below the 2nd centile).

Partial duplication of chromosome 20(pter→q12)
Valter Augusto Della-Rosa 1 and Angela M. Vianna-Morgante 2 Abstract Partial duplication of chromosome 20 (20pter→20q12) resulting from a maternally inherited translocation t(14;20)(q11;q13) is described in a female child with neuropsychomotor retardation and multiple congenital anomalies.To our knowledge this is the largest duplication of chromosome 20 that includes segments of both the short and the long arms thus far described in a live-born child.The karyotype of the child was 46,XX,-14,+der(20), t(14;20)(q11.2;q13.1)mat,and she was diagnosed as having a duplication of the segment 20pter→20q12 and a deletion of 14pter→14q11.1.

DISCUSSION
The patient's karyotype was the result of a type 2 adjacent segregation of the translocation chromosomes and their homologues in maternal meiosis.The material lost from chromosome 14 comprised the short arm, centromere and a small pericentric segment of the long arm.The loss of such segments in Robertsonian translocations does not cause phenotypic abnormalities so that it is reasonable to assume that the patient's clinical picture was the result of chromosome 20 duplication (20pter→ 20q12).
The first report of a child with trisomy of chromosome 20 (Pan et al., 1976) involved a neonate with unusual facial features and multiple congenital malformations who died 4 hours after birth.However, Steele (1990) reanalyzed the chromosomes from a frozen fibroblast culture and identified the extra chromosome as an isochromosome 12p.Indeed, based on the clinical findings, Schinzel (1980) had already suggested that this case represented partial trisomy of an autosomal segment with a banding pattern similar to that of chromosome 20.The same explanation would account for the other presumed trisomy of chromosome 20 reported by Wahlström et al. (1976) in a girl who had an abnormal appearance and cat's cry at birth, and later on showed poor weight gain and psychomotor retardation.
A presumptive 20p and partial 20q duplication was reported by Krmpotic et al. (1971), who were unable to precisely localize the breakpoint on the long arm.More recently, duplications of chromosome 20, involving the short arm and the proximal part of the long arm, have been identified by banding patterns (Marcus et al., 1979, Rudd et al., 1979, Schinzel, 1980;Delicado et al., 1981).In these cases, the propositi had an extra-rearranged chromosome 20 that included small segments of other autosomes.The 20q duplication affected only the band 20q11 (Marcus et al., 1979;Schinzel, 1980;Delicado et al., 1981) or comprised part of 20q12 (Rudd et al., 1979).Our patient had a larger duplication, that included at least the major part of band 20q12.
Table I summarizes the clinical signs of these patients.Most of these signs are associated with 20p duplication (for review, see Grammatico et al., 1992).It is noteworthy that the two patients with the largest 20q duplications (Rudd et al., 1979, and the present case) are the only individuals with severe growth retardation, microcephaly and broad distal phalanges of thumbs and toes.

Figure 1 -
Figure 1 -Patient at the age of 6 years and 9 months.