Haploinsufficiency of NKX2-1 is likely to contribute to developmental delay involving 14q13 microdeletions

Nucleotide variations or deletions in the NK2 homeobox 1 gene (NKX2-1), located at 14q13.3, lead to symptoms associated with the brain, lungs, and thyroid, and the combination of these phenotypes is clinically recognized as the brain-lung-thyroid syndrome. Many types of nucleotide variants of NKX2-1 have been identified, and phenotypic variability has been reported. Chromosomal deletions involving NKX2-1 have also been reported; however, phenotypic differences between patients with nucleotide variants of NKX2-1 and patients with chromosomal deletions involving NKX2-1 have not been well established. Recently, we identified seven patients with 14q13 microdeletions involving the NKX2-1. Most patients exhibited developmental delay. This inquiry arises regarding the potential existence of haploinsufficiency effects beyond those attributed to NKX2-1 within the 14q13 microdeletion. However, a literature review has shown that developmental delay is not rare in patients with nucleotide alterations in NKX2-1. Rather, motor function impairment may have affected the total developmental assessment, and the haploinsufficiency of genes contiguous to NKX2-1 is unlikely to contribute to developmental delay.

Haploinsufficiency of NKX2-1 in Brain-Lung-Thyroid Syndrome with Additional Multiple Pituitary Dysfunction

INTRODUCTION

Heterozygous mutations or haploinsufficiency of NKX2-1 are associated with the brain-lung-thyroid syndrome incorporating primary hypothyroidism, respiratory distress, and neurological disturbances.

CASE PRESENTATION

We report a patient presenting in the neonatal period with multiple pituitary hormone deficiency including central hypothyroidism and hypoadrenalism, growth hormone deficiency, undetectable gonadotrophins, and a small anterior pituitary on MRI. CGH microarray revealed haploinsufficiency for NKX2.1 and during subsequent follow-up, she has exhibited the classic triad of brain-lung-thyroid syndrome with undetectable tissue on thyroid ultrasonography. Whilst the role of NKX2-1 is well described in murine pituitary development, this report constitutes the first description of multiple pituitary dysfunction in humans associated with the syndrome and haploinsufficiency NKX2-1.

CONCLUSION

The report highlights a potential need for pituitary screening in patients with established brain-lung-thyroid syndrome and implicates NKX2.1 in human pituitary disease.

A novel 14q13.1-21.1 deletion identified by CNV-Seq in a patient with brain-lung-thyroid syndrome, tooth agenesis and immunodeficiency

Background

Chromosome 14q11-q22 deletion syndrome (OMIM 613457) is a rare genomic disorder. The phenotype heterogeneity depends on the deletion size, breakpoints and genes deleted. Critical genes like FOXG1, NKX2–1, PAX9 were identified.

Case presentation

We performed whole exome sequencing (WES) and copy number variation sequencing (CNV-seq) for a patient with mild speech and motor developmental delay, short stature, recurrent pulmonary infections, tooth agenesis and triad of brain-lung-thyroid syndrome. By using CNV-seq, we identified a 3.1 Mb de novo interstitial deletion of the 14q13.2q21.1 region encompassing 17 OMIM genes including NKX2–1, PAX9 and NFKBIA. Our patient’s phenotype is consistent with other published 14q13 deletion patients.

Conclusion

Our results showed the combination of WES and CNV-seq is an effective diagnostic strategy for patients with genetic or genomic disorders. After reviewing published patients, we also proposed a new critical region for 14q13 deletion syndrome with is a more benign disorder compared to 14q11-q22 deletion syndrome.

Benign hereditary chorea and deletions outside NKX2-1: What's the role of MBIP?

Heterozygous point mutations or deletions of the NKX2-1 gene cause benign hereditary chorea (BHC) or a various combinations of primary hypothyroidism, respiratory distress and neurological disorders. Deletions proximal to, but not encompassing, NKX2-1 have been described in few subjects with brain-lung-thyroid syndrome. We report on a three-generation Italian family, with 6 subjects presenting BHC and harboring a genomic deletion adjacent to NKX2-1 and including the gene MBIP, recently proposed to be relevant for the pathogenesis of brain-lung-thyroid syndrome. We observed a clear reduction of NKX2-1 transcript levels in fibroblasts from our patients compared to controls; this finding suggests that MBIP deletion affects NKX2-1 expression, mimicking haploinsufficiency caused by classical NKX2-1 related mutations.

A further case of brain-lung-thyroid syndrome with deletion proximal to NKX2-1

Brain-lung-thyroid syndrome (OMIM #610978) is associated with mutations in the NK2 homeobox 1 (NKX2-1) gene, a transcription factor important in development. 50% of patients are affected by the full triad, comprising congenital hypothyroidism, benign hereditary chorea and infant respiratory distress syndrome. Four cases have previously been reported where a patient has features consistent with brain-lung-thyroid syndrome and a chromosome 14q13 deletion adjacent to, but not disrupting, NKX2-1. We present a patient who has a phenotype consistent with brain-lung-thyroid syndrome, featuring congenital hypothyroidism and choreoathetoid movements with gross motor delay. Thyroid ultrasound showed a small-normal gland and spontaneous resolution of hypothyroidism. Array CGH revealed a de novo 14q13.2-3 deletion adjacent to but not directly involving NKX2-1. Sequencing of NKX2-1 was normal. This report highlights a further case of chromosomal deletion adjacent to NXK2-1 in a patient with a phenotype consistent with brain-lung-thyroid syndrome, and confirms that array-CGH is a useful test in the investigation of congenital hypothyroidism. Deletion of the adjacent gene MBIP in most reported cases so far may be relevant to the pathogenesis of brain-lung-thyroid syndrome. Deletion of nearby promoter or enhancer elements acting on NKX2-1 could also be an important factor. However, further work is needed to elucidate the pathogenesis of the brain-lung-thyroid phenotype in such cases.

Novel NKX2-1 Frameshift Mutations in Patients with Atypical Phenotypes of the Brain-Lung-Thyroid Syndrome

OBJECTIVES

To verify the involvement of NKX2-1 gene in infants with brain-lung-thyroid (BLT) syndrome and hypothyroid phenotypes variable among congenital hypothyroidism (CH) or idiopathic mild hypothyroidism (IMH) of postnatal onset.

METHODS

The candidates were selected by a case-finding approach in 130 CH and 53 IMH infants. The NKX2-1 gene was analyzed by direct sequencing and multiplex ligation-dependent probe amplification. The variants were studied in vitro, by expression analyses and luciferase bioassay.

RESULTS

Four cases (3 CH and 1 IMH) consistent with BLT syndrome were identified. Two children were affected with respiratory distress and CH, but wild-type NKX2-1 gene. The remaining two presented choreic movements and no pulmonary involvement, but discrepant thyroid phenotypes: one had severe CH with lingual ectopy and the other one IMH with gland in situ. They were carriers of new de novo heterozygous frameshift mutations of NKX2-1 (c.177delG and c.153_166del14). The c.177delG leads to a prematurely truncated protein (p.H60TfsX11) with undetectable activity in vitro. The c.153_166del14 leads to the generation of an elongated aberrant protein (p.A52RfsX351) able to translocate into the nucleus, but completely inactive on a responsive promoter.

CONCLUSIONS

Two novel heterozygous frameshift mutations of NKX2-1 were identified in 2 cases selected on the basis of a BLT-like phenotype among 183 hypothyroid infants. The atypical hypothyroid phenotypes of these 2 children (CH with lingual ectopy or IMH of postnatal onset) further expand the clinical spectrum that can be associated with NKX2-1 mutations.