Trisomy 4q Syndrome: A rare Syndrome Phenotypically Similar to Trisomy 18

摘要

Trisomy 4q syndrome is rare and has been reported in only in a limited number of cases. We describe a case of trisomy 4q syndrome misdiagnosed as trisomy 18 syndrome due to anomalies seen on antenatal ultrasound. Postnatal chromosome analysis revealed an unbalanced translocation between the long arms of chromosome 4 and 18 leading to duplication of the majority of 4q and a small deletion of distal 18q. The infant had unique clinical features including an absent right thumb and claw like-fingers on both hands which to our knowledge have not been previously described in patients with Trisomy 4q. Several similar congenital anomalies are associated with trisomy 4q syndrome and trisomy 18. It is important that perinatologists, obstetricians and neonatologists be aware of trisomy 4q, its similarity to trisomy 18, and the possibility of misdiagnosing patients prenatally if amniocentesis and chromosomal analysis are not performed. Introduction Trisomy 4q syndrome is a rare condition, first described in 1971, that often presents with multiple debilitating congenital anomalies.1 Trisomy 4q has been reported to occur due to multiple genetic mechanisms including inheritance of unbalanced translocations, 2,3,4,5 insertions,6,7 or duplications8,9,10 and by de novo unbalanced translocations.11,12,13 Interestingly, the most common chromosome site involved in unbalanced translocations with 4q appears to be the distal band of chromosome 18q. 3, 4Although, in most of cases of trisomy 4q, the majority of 4q is duplicated, the breakpoint on 4q may vary; in cases of unbalanced translocation, a small deletion of another chromosome may accompany trisomy 4q. Therefore, although most cases have similar anomalies, the variability in breakpoints and involvement of other minor chromosome anomalies may result in different phenotypes. We present an infant with distinctive phenotypic features as a result of an unbalanced translocation resulting in trisomy 4q and deletion of the distal portion of 18q. Case Report The serum biochemical markers in a 32 year old gravida 5, para 3 Hispanic pregnant female were suggestive of fetal Trisomy 18 with a risk of >1 in 10. She was referred to the University of Kansas Medical center (KUMED) for detailed ultrasound evaluation and genetic counseling. Anomalies identified by ultrasound at KUMED included a large atrial septal defect, a single umbilical artery, stubby and malformed fingers of one hand (Figure 1), and unilateral multicystic kidney (Figure 2). As there was a high index of suspicion of fetal aneuploidy the woman was counseled about cytogenetic confirmation; but she declined amniocentesis.