CASE REPORT
Prenatal diagnosis and molecular genetic analysis of short rib-polydactyly
syndrome type III (Verma-Naumoff) in a second-trimester fetus with a
homozygous splice site mutation in intron 4 in the NEK1 gene
Chih-Ping Chen a,b,c,d,e,f,g*, Schu-Rern Chern b, Tung-Yao Chang h, Yi-Ning Su i, Yi-Yung Chen a, Jun-Wei Su a,j and Wayseen Wang b,k
a Department of Medicine, Mackay Medical College, New Taipei City, Taiwan
b Department of Obstetrics and Gynecology, Mackay Memorial Hospital, Taipei, Taiwan c Department of Medical Research, Mackay Memorial Hospital, Taipei, Taiwan
d Department of Biotechnology, Asia University, Taichung, Taiwan
e School of Chinese Medicine, College of Chinese Medicine, China Medical University, Taichung, Taiwan f Institute of Clinical and Community Health Nursing, National Yang-Ming University, Taipei, Taiwan g Department of Obstetrics and Gynecology, School of Medicine, National Yang-Ming University, Taipei,
Taiwan
h Taiji Fetal Medicine Center, Taipei, Taiwan
i Department of Medical Genetics, National Taiwan University Hospital, Taipei, Taiwan
j Department of Obstetrics and Gynecology, China Medical University Hospital, Taichung, Taiwan k Department of Bioengineering, Tatung University, Taipei, Taiwan
* Correspondence to: Chih-Ping Chen, MD
Department of Obstetrics and Gynecology, Mackay Memorial Hospital 92, Section 2, Chung-Shan North Road, Taipei, Taiwan
Tel: +886-2-25433535; Fax: +886-2-25433642, +886-2-25232448 E-mail: [email protected]
Short title: Short rib-polydactyly syndrome type III
Abstract
Objective: To demonstrate perinatal imaging findings and to investigate the mutation in the
NEK1 gene in a fetus with type III short rib-polydactyly syndrome (SRPS) (Verma-Naumoff).
Case Report: A 34-year-old woman with no past history of fetal SRPS was referred to the
hospital at 21 weeks of gestation because of sonographic diagnosis of short limbs in the fetus. Fetal ultrasound revealed a narrow thorax, short ribs, short limbs with marginal spurs, and postaxial hexadactyly in both hands and feet. A diagnosis of SRPS III (Verma-Naumoff) was made. Amniocentesis was performed. The karyotype was 46,XY. Molecular genetic analysis of the amniotic fluid cells identified a homozygous splice site mutation in intron 4 (c.331-1 A>G) or IVS4-1 A>G in the NEK1 gene. The parents were heterozygous for the mutation. The pregnancy was subsequently terminated and a malformed fetus was delivered with prominent forehead, a flattened nasal bridge, a narrow and short trunk, a protuberant abdomen, bilateral postaxial polydactyly and syndactyly of the hands and feet, and micromelic limbs. No facial cleft or genital abnormality was noted. The radiograph was consistent with SRPS III.
Conclusion: Polydactyly, micromelia, metaphyseal spurs, widened humeral metaphyses and
shortened ribs can be prominent prenatal ultrasound findings of SRPS III. The present case provides evidence for a correlation of a mutation in the NEK1 gene with SRPS III.
Key words: NEK1, prenatal diagnosis, short rib-polydactyly syndrome type III
Introduction
Short rib-polydactyly syndromes (SRPSs) are a group of autosomal recessive osteochondrodysplasias caused by ciliary dysfunction and characterized by short ribs, polydactyly, short limbs, multiple abnormalities of the internal organs including kidneys, heart, liver, pancreas, genitalia and intestines. Five types of SRPS have been recognized such as SRPS I (Saldino-Noonan) (OMIM 263530), SRPS II (Majewski) (OMIM 263520), SRPS III (Verma-Naumoff) (OMIM 263510), SRPS IV (Beemer-Langer) (OMIM 269860) and SRPS V (OMIM 614091). The different subtypes of SRPS may be a single genetic disorder with variable expressivity because of significant phenotypic overlap in different subtypes [1]. SRPS III (Verma-Naumoff) is characterized by polydactyly, micromelia, metaphyseal spurs and occasional situs inversus totalis [2-3]. Here, we present our experience of prenatal diagnosis and molecular genetic analysis of SRPS III in a second-trimester fetus associated with a homozygous splice site mutation in intron 4 in the NEK1 gene. Such an association is novel and has not been previously described.
Case Report
A 34-year-old, gravida 3, para 1, woman had undergone amniocentesis at 17 weeks of gestation because of advanced maternal age, and the result revealed a karyotype of 46,XY. Her husband was 46 years old. The woman and her husband were non-consanguineous, and they had a healthy 6-year-old daughter. The woman had experienced spontaneous abortion twice, but cytogenetic analysis of the couple had revealed normal karyotypes. During this pregnancy, the pregnancy was uneventful until 21 weeks of gestation when level II ultrasound revealed a narrow thorax, short ribs, short limbs with marginal spurs, and postaxial hexadactyly in both hands and feet in the fetus (Fig. 1). The thoracic circumference (TC) was 12.17 cm (< 5th centile), and the abdominal circumference (AC) was 17.58 cm (75th centile). The TC/AC ratio was 0.69. The lengths of the long bones were under the 5th centile on nomograms. The femur, tibia, fibula, humerus, radius (curved) and ulna (curved) were measured 2.64 cm, 2.03 cm, 1.90 cm, 2.40 cm, 2.05 cm and 2 cm, respectively. The biparietal diameter, head circumference and amniotic fluid amount were normal. Internal organs were unremarkable. A diagnosis of SRPS III (Verma-Naumoff) was made. Repeated amniocentesis was performed. Molecular genetic analysis of the amniotic fluid cells identified a homozygous splice site mutation in intron 4 (c.331-1 A>G) or IVS4-1 A>G in the NEK1 gene (Fig. 2). The parents were heterozygous for the mutation (Fig. 2). Molecular analysis
of the amniotic fluid cells revealed no mutations in the DYNC2H1 gene. The pregnancy was subsequently terminated at 22 weeks of gestation. A 552-g male fetus was delivered with prominent forehead, a flattened nasal bridge, a narrow and short trunk, a protuberant abdomen, bilateral postaxial polydactyly and syndactyly of the hands and feet, and micromelic limbs (Fig. 3). No facial cleft or genital abnormality was noted. Postnatal molecular analysis of the fetal tissues confirmed the prenatal diagnosis. The radiograph was consistent with SRPS III (Fig. 4).
Discussion
Prenatal diagnosis of SRPS III has been well described [2-5]. Characteristic ultrasound features include widened humeral metaphyses with marginal spurs, postaxial polydactyly and shortened ribs [5]. The peculiar aspect of this case is the prenatal diagnosis of a NEK1 mutation in a fetus with SRPS III.
The NEK1 gene is located at 4q33 and encodes never in mitosis gene A-related kinase 1 (NEK1). NEK1 is the first mammalian ortholog of the fungal protein kinase of never in mitosis A in Aspergillus nidulans [6]. The NEK1 protein is localized to the basal body region of the cilium, and over-expression of NEK1 inhibits ciliogenesis [7]. The NEK1 is involved in a DNA damage sensing/repair pathway and functions in DNA damage response and checkpoint control [8-9]. The NEK1 also affected primary cilium formation [7]. Thus NEK1 plays a role in centromere integrity affecting both ciliogenesis and chromosome stability [10]. Mutant mice for Nek1 kinase (kat mice) have been shown to present an autosomal recessive pleiotropic phenotype that includes progressing polycystic kidney disease, choroid plexus cysts, male sterility, dwarfing, abnormal olfactory lobes, facial dysmorphism, hydrocephalus, uremia and anemia [11-13]. Thiel et al [14] first reported the association of NEK1 mutations with SRPS. They identified a homozygous R127X mutation in the NEK1 gene in an affected individual with SRPS II, a homozygous splice site mutation of c.869-2 A>G in intron 10 in the NEK1 gene in another individual with SRPS II, and a heterozygous 1-bp insertion (c.1640_1641insA) in the NEK1 gene and a heterozygous G3916D missense mutation in the DYNC2H1 gene in the third individual with SRPS II. Thiel et al [14] also found that absence of functional full-length NEK1 severely reduces cilia number and alters cilia morphology in vivo. Our report additionally shows the association of NEK1 mutation with SRPS and provides evidence that a homozygous splice site mutation in intron 4 in the NEK1 gene can cause SRPS III.
In addition to the NEK1 gene, other genes such as DYNC2H1 and IFT80 have been reported to be associated with SRPS III. Dagoneau et al [15] identified mutations in DYNC2H1 in two fetuses with SRPS III. One fetus had compound heterozygous mutations of Q1537R and G2461V in DYNC2H1, and the other fetus had compound heterozygous mutations of T1987A and 10130delT in DYNC2H1. Merrill et al [16] detected compound heterozygous mutations in DYNC2H1 in two patients with SRPS III and homozygous mutation in one patient with SRPS III. One patient had a homozygous mutation of R587C in DYNC2H1, another patient had compound heterozygous mutations of R2205H and R2838X in DYNC2H1, and the third patient had compound heterozygous mutations of F209I and IVS33+1 G>T in DYNC2H1. Cavalcanti et al [17] reported a homozygous mutation of G241R in IFT80 in a fetus with SRPS III.
In summary, this presentation demonstrates perinatal imaging findings of polydactyly, micromelia, metaphyseal spurs, widened humeral metaphyses and shortened ribs in a fetus with SRPS III. The present case provides evidence for a correlation of a mutation in the NEK1 gene with SRPS III.
Acknowledgements
This work was supported by research grants NSC-97-2314-B-195-006-MY3 and NSC-99-2628-B-195-001-MY3 from the National Science Council, and MMH-E-100-04 from Mackay Memorial Hospital, Taipei, Taiwan.
References
1. Elçioglu NH, Hall CM. Diagnostic dilemmas in the short rib-polydactyly syndrome group. Am J Med Genet 2002; 111: 392-400.
2. Chen C-P, Tzen C-Y. Short rib-polydactyly syndrome type III (Verma-Naumoff) in a third-trimester
fetus with unusual associations of epiglottic hypoplasia, renal cystic dysplasia, pyelectasia and oligohydramnios. Prenat Diagn 2001; 21: 1101-2.
3. Chen C-P, Chang T-Y, Tzen C-Y, Lin C-J, Wang W. Sonographic detection of situs inversus totalis,
ventricular septal defect, and short rib-polydactyly syndrome type III (Verma-Naumoff) in a second-trimester fetus not known to be at risk. Ultrasound Obstet Gynecol 2002; 19: 629-31.
4. Wu M-H, Kuo P-L, Lin S-J. Prenatal diagnosis of recurrence of short rib-polydactyly syndrome. Am J Med Genet 1995; 55: 279-84.
5. Meizner I, Barnhard Y. Short-rib polydactyly syndrome (SRPS) type III diagnosed during routine
prenatal ultrasonographic screening. A case report. Prenat Diagn 1995; 15: 665-8.
6. Letwin K, Mizzen L, Motro B, Ben-David Y, Bernstein A, Pawson T. A mammalian dual specificity
protein kinase, Nek1, is related to the NIMA cell cycle regulator and highly expressed in meiotic germ cells. EMBO J 1992; 10: 3521-31.
7. Shalom O, Shalva N, Altschuler Y, Motro B. The mammalian Nek1 kinase is involved in primary cilium
formation. FEBS Lett 2008; 582: 1465-70.
8. Chen Y, Chen P-L, Chen C-F, Jiang X, Riley DJ. Never-in-mitosis related kinase 1 functions in DNA
damage response and checkpoint control. Cell Cycle 2008; 7: 3194-201.
9. Chen Y, Chen C-F, Chiang H-C, Pena M, Polci R, Wei R-L, et al. Mutation of NIMA-related kinase 1
(NEK1) leads to chromosome instability. Mol Cancer 2011; 10: 5.
10.White MC, Quarmby LM. The NIMA-family kinase, Nek1 affects the stability of centrosomes and
ciliogenesis. BMC Cell Biol 2008; 9: 29.
11.Janaswami PM, Birkenmeier EH, Cook SA, Rowe LB, Bronson RT, Davisson MT. Identification and
genetic mapping of a new polycystic kidney disease on mouse chromosome 8. Genomics 1997; 40: 101-7.
12.Vogler C, Homan S, Pung A, Thorpe C, Barker J, Birkenmeier EH, et al. Clinical and pathological
findings in two new allelic murine models of polycystic kidney disease. J Am Soc Nephrol 1999; 10: 2534-9.
13.Upadhya P, Birkenmeier EH, Birkenmeier CS, Barker JE. Mutations in a NIMA-related kinase gene, Nek1, cause pleiotropic effects including a progressive polycystic kidney disease in mice. PNAS 2000;
97: 217-21.
14.Thiel C, Kessler K, Giessl A, Dimmler A, Shalev SA, von der Haar S, et al. NEK1 mutations cause
15.Dagoneau N, Goulet M, Geneviève D, Sznajer Y, Martinovic J, Smithson S, et al. DYNC2H1 mutations
cause asphyxiating thoracic dystrophy and short rib-polydactyly syndrome, type III. Am J Hum Genet 2009; 84: 706-11.
16.Merrill AE, Merriman B, Farrington-Rock C, Camacho N, Sebald ET, Funari VA, et al. Ciliary
abnormalities due to defects in the retrograde transport protein DYNC2H1 in short-rib polydactyly syndrome. Am J Hum Genet 2009; 84: 542-9.
17.Cavalcanti DP, Huber C, Le Quan Sang K-H, Baujat G, Collins F, Delezoide A-L, et al. Mutation in IFT80 in a fetus with the phenotype of Verma-Naumoff provides molecular evidence for
Jeune-Verma-Naumoff dysplasia spectrum. J Med Genet 2011; 48: 88-92.
Figure Legends
Fig. 1. Prenatal ultrasound at 21 weeks of gestation shows (A) polydactyly of the foot, (B) polydactyly of the hand, (C) short ribs and a narrow chest, (D) curved radius, (E) curved ulna, (F) marginal spurs (arrows) in tibia and (G) widened humeral metaphyses (arrows). H = heart.
Fig. 2. A heterozygous splice site mutation in intron 4 (c.331-1, A>G) or IVS4-1 A>G in the NEK1 gene in the father and the mother, and a homozygous mutation of NEK1, IVS4-1 A>G in the fetus. Fig. 3. The fetus at birth. (A) Whole body view, (B) craniofacial appearance, (C) polydactyly and
syndactyly of the hands, and (D) polydactyly and syndactyly of the feet. Fig. 4. The radiograph of the fetus.
