Prenatal detection of de novo inversion of chromosome 9 with duplicated heterochromatic region and postnatal follow-up

Pericentric Inversion of Chromosome 9 in Twins With Cyclopia: A Rare Entity

Pericentric inversion of chromosome 9 (inv(9)) is one of the most common variants seen in a normal human karyotype that occurs during meiosis. Despite being categorized as a normal variant, some studies using classical cytogenetics have recently shown that inv(9) could be associated with azoospermia, congenital anomalies, growth retardation, and rarely with abnormal karyotype. However, there is no reported association with cyclopia. Interestingly this genetic variant involves twin fetuses. A 36-year-old multiparous lady with dichorionic diamniotic twin pregnancy presented to the fetomaternal unit with fetal growth restriction at 34 weeks of gestation. An ultrasound scan revealed both have microcephaly, fisting hands, holoprosencephaly, and proboscis suspicious of Patau syndrome. Amniocentesis was not issued due to late pregnancy and guarded prognosis. The mother presented with pre-eclampsia at 35 weeks of gestation. The pregnancy managed to prolong up to 36 weeks after which caesarean section was performed due to the leading twin being in a transverse lie. Two baby twin girls were born 3 minutes apart with microcephaly and cyclops appearance. Chromosomal analysis of both twins revealed similar karyotypes of 46, XX, inv(9)(p11,q13). Pericentric inversion of chromosome 9 is regarded as a normal chromosomal variation in the general population, but in twins with cyclops is considered rare. Early referral to a tertiary hospital for twin management is highly required. It may identify fetuses with such abnormalities and counsel the parents with appropriate management.

A Balanced Translocation in Kallmann Syndrome Implicates a Long Noncoding RNA, RMST, as a GnRH Neuronal Regulator

CONTEXT

Kallmann syndrome (KS) is a rare, genetically heterogeneous Mendelian disorder. Structural defects in KS patients have helped define the genetic architecture of gonadotropin-releasing hormone (GnRH) neuronal development in this condition.

OBJECTIVE

Examine the functional role a novel structural defect affecting a long noncoding RNA (lncRNA), RMST, found in a KS patient.

DESIGN

Whole genome sequencing, induced pluripotent stem cells and derived neural crest cells (NCC) from the KS patient were contrasted with controls.

SETTING

The Harvard Reproductive Sciences Center, Massachusetts General Hospital Center for Genomic Medicine, and Singapore Genome Institute.

PATIENT

A KS patient with a unique translocation, t(7;12)(q22;q24).

INTERVENTIONS/MAIN OUTCOME MEASURE/RESULTS

A novel translocation was detected affecting the lncRNA, RMST, on chromosome 12 in the absence of any other KS mutations. Compared with controls, the patient's induced pluripotent stem cells and NCC provided functional information regarding RMST. Whereas RMST expression increased during NCC differentiation in controls, it was substantially reduced in the KS patient's NCC coincident with abrogated NCC morphological development and abnormal expression of several "downstream" genes essential for GnRH ontogeny (SOX2, PAX3, CHD7, TUBB3, and MKRN3). Additionally, an intronic single nucleotide polymorphism in RMST was significantly implicated in a genome-wide association study associated with age of menarche.

CONCLUSIONS

A novel deletion in RMST implicates the loss of function of a lncRNA as a unique cause of KS and suggests it plays a critical role in the ontogeny of GnRH neurons and puberty.

De novo pericentric inversion of chromosome 9 in congenital anomaly

PURPOSE

The pericentric inversion of chromosome 9 is one of the most common structural balanced chromosomal variations and has been found in both normal populations and patients with various abnormal phenotypes and diseases. The aim of this study was to re-evaluate the clinical impact of inv(9)(p11q13).

MATERIALS AND METHODS

We studied the karyotypes of 431 neonates with congenital anomalies at the Pediatric Clinic in Ajou University Hospital between 2004 and 2008 and retrospectively reviewed their clinical data.

RESULTS

Chromosomal aberrations were detected in 60 patients (13.9%). The most common type of structural abnormality was inv(9)(p11q13), found in eight patients. Clinical investigation revealed that all eight cases with inv(9)(p11q13) had various congenital anomalies including: polydactyly, club foot, microtia, deafness, asymmetric face, giant Meckel's diverticulum, duodenal diaphragm, small bowel malrotation, pulmonary stenosis, cardiomyopathy, arrhythmia, and intrauterine growth restriction. The cytogenetic analysis of parents showed that all of the cases were de novo heterozygous inv(9)(p11q13).

CONCLUSION

Since our results indicate that the incidence of inv(9)(p11q13) in patients with congenital anomalies was not significantly different from the normal population, inv(9)(p11q13) does not appear to be pathogenic with regard to the congenital anomalies. Some other, to date unknown, causes of the anomalies remain to be identified.