Comprehensive genotyping and clinical characterisation reveal 27 novel NKX2-1 mutations and expand the phenotypic spectrum.
BACKGROUND
NKX2-1 encodes a transcription factor with large impact on the development of brain, lung and thyroid. Germline mutations of NKX2-1 can lead to dysfunction and malformations of these organs. Starting from the largest coherent collection of patients with a suspected phenotype to date, we systematically evaluated frequency, quality and spectrum of phenotypic consequences of NKX2-1 mutations.


METHODS
After identifying mutations by Sanger sequencing and array CGH, we comprehensively reanalysed the phenotype of affected patients and their relatives. We employed electrophoretic mobility shift assay (EMSA) to detect alterations of NKX2-1 DNA binding. Gene expression was monitored by means of in situ hybridisation and compared with the expression level of MBIP, a candidate gene presumably involved in the disorders and closely located in close genomic proximity to NKX2-1.


RESULTS
Within 101 index patients, we detected 17 point mutations and 10 deletions. Neurological symptoms were the most consistent finding (100%), followed by lung affection (78%) and thyroidal dysfunction (75%). Novel symptoms associated with NKX2-1 mutations comprise abnormal height, bouts of fever and cardiac septum defects. In contrast to previous reports, our data suggest that missense mutations in the homeodomain of NKX2-1 not necessarily modify its DNA binding capacity and that this specific type of mutations may be associated with mild pulmonary phenotypes such as asthma. Two deletions did not include NKX2-1, but MBIP, whose expression spatially and temporarily coincides with NKX2-1 in early murine development.


CONCLUSIONS
The high incidence of NKX2-1 mutations strongly recommends the routine screen for mutations in patients with corresponding symptoms. However, this analysis should not be confined to the exonic sequence alone, but should take advantage of affordable NGS technology to expand the target to adjacent regulatory sequences and the NKX2-1 interactome in order to maximise the yield of this diagnostic effort.
Institute for Experimental Pediatric Endocrinology, Charité University Medicine, Berlin, Germany Max Planck Institute for Molecular Genetics, Berlin, Germany.
Anne
A
Thorwarth
Institute for Experimental Pediatric Endocrinology, Charité University Medicine, Berlin, Germany.
Sarah
S
Schnittert-Hübener
Institute for Experimental Pediatric Endocrinology, Charité University Medicine, Berlin, Germany.
Pamela
P
Schrumpf
Max Planck Institute for Molecular Genetics, Berlin, Germany.
Ines
I
Müller
Institute for Experimental Pediatric Endocrinology, Charité University Medicine, Berlin, Germany.
Sabine
S
Jyrch
Department of Neonatology, Charité University Medicine, Berlin, Germany.
Christof
C
Dame
Institute for Experimental Pediatric Endocrinology, Charité University Medicine, Berlin, Germany.
Heike
H
Biebermann
Institute for Experimental Pediatric Endocrinology, Charité University Medicine, Berlin, Germany.
Gunnar
G
Kleinau
Department of Neurology, Charité University Medicine, Berlin, Germany.
Juri
J
Katchanov
Department of Neuropediatrics, Charité University Medicine, Berlin, Germany.
Markus
M
Schuelke
Max Planck Institute for Molecular Genetics, Berlin, Germany.
Grit
G
Ebert
Max Planck Institute for Molecular Genetics, Berlin, Germany.
Anne
A
Steininger
Neuromuscular and Neurogenetic Disorders of Childhood Section, National Institute of Neurological Disorders and Stroke, NIH, Bethesda, Maryland, USA.
Carsten
C
Bönnemann
Interdisciplinary Pediatric Center for Children with Developmental Disabilities and Severe Chronic Disorders, University Medical Center, Georg August University, Göttingen, Germany.
Knut
K
Brockmann
Department for Neuropediatrics, Children's and Youth Hospital "Auf der Bult", Hannover, Germany.
Hans-Jürgen
HJ
Christen
Division of Pediatric Endocrinology & Diabetes, John Hunter Children's Hospital, Newcastle, Australia.
Patricia
P
Crock
Department of Woman and Child, University of Leuven, Leuven, Belgium.
Francis
F
deZegher
Dr. von Haunersches Kinderspital, Member of the German Center for Lung Research, University of Munich, Munich, Germany.
Matthias
M
Griese
Division of Endocrinology & Diabetes, Royal Children's Hospital Melbourne, Melbourne, Australia.
Jacqueline
J
Hewitt
Department of Clinical Sciences- Pediatric Endocrinology, University Hospital MAS, Malmö, Sweden.
Sten
S
Ivarsson
Department of Neuropediatrics, Charité University Medicine, Berlin, Germany.
Christoph
C
Hübner
Department of Pediatric and Adolescent Medicine, Medical University of Innsbruck, Innsbruck, Austria.
Klaus
K
Kapelari
Division of Child Neurology, University Childrens Hospital Zurich, Zurich, Switzerland.
Barbara
B
Plecko
Department for Neuropediatrics, Heidelberg University Hospital, Heidelberg, Germany.
Dietz
D
Rating
Department of Paediatric Endocrinology Screening and Functional Endocrine Diagnostics, University Paediatric Hospital, Medical University Sofia, Sofia, Bulgaria.
Iva
I
Stoeva
Max Planck Institute for Molecular Genetics, Berlin, Germany.
Hans-Hilger
HH
Ropers
Institute for Experimental Pediatric Endocrinology, Charité University Medicine, Berlin, Germany.
Annette
A
Grüters
Max Planck Institute for Molecular Genetics, Berlin, Germany.
Reinhard
R
Ullmann
Institute for Experimental Pediatric Endocrinology, Charité University Medicine, Berlin, Germany.
Heiko
H
Krude
D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D055028:Comparative Genomic Hybridization; D056915:DNA Copy Number Variations / Q000235:genetics; D024202:Electrophoretic Mobility Shift Assay; D005260:Female; D017353:Gene Deletion; D030342:Genetic Diseases, Inborn / Q000235:genetics / Q000503:physiopathology; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D009687:Nuclear Proteins / Q000235:genetics*; D010641:Phenotype; D017354:Point Mutation / Q000235:genetics; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors / Q000235:genetics*
D009687:Nuclear Proteins; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors
CNV; NKX2-1; array CGH; choreoathetosis; hypothyroidism