ABSTRACT

Partial duplication of chromosome 3q is a recognizable syndrome with characteristic facial features, microcephaly, digital anomalies, genitourinary and cardiac defects as well as growth retardation and developmental delays. While there is clinical overlap with the unrelated Cornelia de Lange syndrome (CDLS), there are distinguishing features and molecular etiologies. Most cases of 3q duplication appear to be the result of an unbalanced translocation or inversion and therefore accompanied by additional cytogenetic anomalies. Consequently, pure duplications of 3q are very rare; we are aware of only 12 such cases that have been reported previously. Here, we present a new case of pure, partial 3q duplication in a 3-month-old female who displayed a number of clinical signs consistent with previously reported phenotypes and the additional novel finding of a vascular ring.

1. INTRODUCTION

Individuals with partial duplication of chromosome 3q typically display characteristic facial features including low frontal hairline, bushy eyebrows, synophrys, hypertelorism, long eyelashes, downslanting palpebral fissures, epicanthal folds, wide nasal bridge with bulbous nasal tip, prominent philtrum, down-turned corners of the mouth and low-set, malformed ears. Additional physical findings include microcephaly, digital anomalies such as brachydactyly and clinodactyly, hirsutism, genitourinary and cardiac defects in addition to preand postnatal growth retardation and developmental delay [1]. Less common reported features include ocular anomalies, neuroimaging findings, hip dysplasia, central sleep apnea and conductive hearing loss [2]. Approximately one-third of patients die within the first year of life due to infections and cardiac anomalies [3]. Although 3q duplication syndrome has overlapping features with and clinically resembles the unrelated Cornelia de Lange syndrome (CDLS), there are distinguishing features and molecular etiologies. Most cases of 3q duplication appear to be the result of an unbalanced translocation or inversion; as a result, there is often an accompanying cytogenetic anomaly such as deletion of another chromosomal segment [4]. Therefore, pure duplications of 3q are very rare; we are aware of only 12 such cases that have been reported previously [2, 6]. Here, we present a new case of a pure, partial 3q duplication in a 3-month-old female who displayed a number of clinical signs consistent with previously reported phenotypes and the additional novel finding of a vascular ring.

2. CASE REPORT

A Hispanic female, the third child of non-consanguineous parents, was born after an unremarkable pregnancy at 38 weeks gestation. Birth weight was at the 10th to 25th percentile with length and head circumference at minus 2 to minus 3 standard deviations and 50 - 75th percentile, respectively. The patient was admitted to the Neonatal Intensive Care Unit for meconium aspiration, jaundice and asymmetric growth retardation. She was noted to have a wide and open anterior fontanelle, hypertrichosis with overgrowth of scalp hair onto the forehead, synophrys, bushy eyebrows, anteverted nares, long philtrum, downturned corners of the mouth, low-set and malformed pinnae, maxillary prognathism and retrognathia (Figure 1C). The nipples were laterally displaced and the hands showed bilateral 5th finger clinodactyly and bilateral single palmer creases. A chromosomal microarray was requested because of the aforementioned dysmorphology.

At one month of age, the patient was readmitted with respiratory distress that progressed to respiratory failure and was found to be positive for metapneumovirus. She failed extubation, prompting a bronchoscopy which identified tracheomalacia. A brain MRI and EEG were normal. Further workup included a multislice computed tomography (MSCT) showing double aortic arch with fourvessel sign and narrowing of the distal trachea above the carina consistent with a vascular ring (Figures 2(a) and (b)). An echocardiogram additionally noted a very small patent ductus arteriosus with small left-to-right shunt. The patient underwent a PDA ligation and division of the vascular ring. At the time of this report, the patient was 3 months old and at 14 days post-operative; she remained with a tracheostomy.

3. METHODS

EDTA-anticoagulated blood of the patient, and subsequently her parents were sent to the MSU Clinical Genetics Laboratory for both genome-wide SNP microarray and cytogenetic analysis. Genome-wide microarray-CGH analysis was performed using Affymetrix cytogenetics whole genome 2.7 M array with 2.7 million markers including 2,361,876 non-polymorphic probes/markers and 400,103 SNP probes/markers. Genomic DNA was extracted from whole blood, then amplified and purified. Following denaturation of probe DNA, hybridization was carried out with the Affymetrix cytogenetic 2.7 M array assay kit following the manufacturers’ standard protocol. The data was analyzed by ChAS (Chromosome Analysis Suite) and compared against a reference model file provided by Affymetrix to detect gains and losses. Chromosome slides were made by conventional methods from

phytohaemagglutinin-stimulated peripheral blood cultures. Subsequently, routine chromosome analysis was performed on standard GTG-banded metaphase spreads. High resolution genome wide microarray-CGH analysis revealed a copy number gain of 29,436 probes in the region of 3q24q28 (Figure 1A) indicating a duplication estimated to be at least 45.6 Mb in size. Chromosome analysis confirmed this to be a segmental duplication (Figure 1B). Parental karyotypes were normal (data not shown), confirming the patient’s 3q duplication was a de novo occurrence.

4. DISCUSSION

Pure duplications of chromosome 3q are rare as the majority appear to occur in conjunction with other structural anomalies such as unbalanced translocations and insertions [7,10]. This report represents a new case of pure 3q duplication due to a de novo interstitial duplication event detected in a 3-month-old female with multiple congenital anomalies, tracheomalacia and vascular compression from a double aortic arch. Until now, only 12 cases of pure 3q duplication have been reported. Table 1 summarizes the clinical features of these cases, including our patient.

Table 1. Clinical summary of thirteen pure 3q duplication patients.

¹Incidence among 12 previously published cases, n/a not applicable; + present, − absent/not reported [2,3,5,7-9,11,12,21-23].

A specific critical region responsible for the phenotype has yet to be clearly defined, but it has been suggested to be between 3q26.3 to 3q27 [11] or 3q26.3 to 3q29 [3,7]. By comparing the phenotype of our patient with those of other pure 3q duplications, evidence for previously proposed critical regions is supported and suggests that the minimal region of overlap may be at band 3q26.3 [3,10]. This region therefore may contain the gene(s) responseble for the dup(3q) phenotype.

Duplication 3q syndrome has attracted particular interest because of its recurrent features and the clinical similarity to CDLS. Similarities in the facial features of children with duplication 3q and CDLS have been repeatedly noted [12-14].

5. CONCLUSION

Our patient represents the thirteenth case of pure partial trisomy 3q, with features consistent with those previously reported. We additionally report the novel finding of a vascular ring. The availability of increasingly dense microarray technology, whole exome and full genome sequencing will undoubtedly result in further clarification of the phenotype and natural history of this rare and poorly defined syndrome.

REFERENCES