Short-Rib Thoracic Dysplasia 3 With Or Without Polydactyly

A number sign (#) is used with this entry because of evidence that short-rib thoracic dysplasia-3 with or without polydactyly (SRTD3) is caused by homozygous or compound heterozygous mutation in the DYNC2H1 gene (603297) on chromosome 11q22. There is also evidence that SRTD can be caused by digenic biallelic mutation in the DYNC2H1 and NEK1 (604588) genes.

Description

Short-rib thoracic dysplasia (SRTD) with or without polydactyly refers to a group of autosomal recessive skeletal ciliopathies that are characterized by a constricted thoracic cage, short ribs, shortened tubular bones, and a 'trident' appearance of the acetabular roof. SRTD encompasses Ellis-van Creveld syndrome (EVC) and the disorders previously designated as Jeune syndrome or asphyxiating thoracic dystrophy (ATD), short rib-polydactyly syndrome (SRPS), and Mainzer-Saldino syndrome (MZSDS). Polydactyly is variably present, and there is phenotypic overlap in the various forms of SRTDs, which differ by visceral malformation and metaphyseal appearance. Nonskeletal involvement can include cleft lip/palate as well as anomalies of major organs such as the brain, eye, heart, kidneys, liver, pancreas, intestines, and genitalia. Some forms of SRTD are lethal in the neonatal period due to respiratory insufficiency secondary to a severely restricted thoracic cage, whereas others are compatible with life (summary by Huber and Cormier-Daire, 2012 and Schmidts et al., 2013).

There is phenotypic overlap with the cranioectodermal dysplasias (Sensenbrenner syndrome; see CED1, 218330).

For a discussion of genetic heterogeneity of short-rib thoracic dysplasia, see SRTD1 (208500).

Clinical Features

Saldino and Noonan (1972) described 2 stillborn female sibs and an unrelated stillborn infant who had severe thoracic dystrophy, micromelia, hypoplastic long bones, and multiple internal congenital anomalies. Postaxial polydactyly in 1 sib was present in 3 extremities, with 6 fingers on the right hand and 7 on the left, and 6 toes on the left foot; her sib had 7 rudimentary fingers of the hands, with nail beds but no nails, and both feet had 5 rudimentary toes without nail beds. Their limbs were severely shortened and flipper-like, with striking metaphyseal dysplasia of tubular bones. Ossification was defective in the calvaria, vertebrae, pelvis, and bones of the hands and feet. The tubular bones were short, with marked metaphyseal irregularities. Saldino and Noonan (1972) noted that in these patients the pelvis resembled that of patients with a diagnosis of Ellis-van Creveld syndrome or asphyxiating thoracic dystrophy, with small ilia and osseous spurs projecting medially and laterally from the acetabular roofs. In addition, the sibs exhibited polycystic kidneys, transposition of great vessels, and atretic lesions of the gastrointestinal and genitourinary systems. Saldino and Noonan (1972) suggested that this was a 'new' malformation syndrome (SRPS I) similar to EVC and ATD.

Richardson et al. (1977) described affected sibs with a phenotype similar to that of the sibs described by Saldino and Noonan (1972).

Verma et al. (1975) reported a consanguineous family in which 6 of 9 conceptions had a short-limbed lethal dwarfism manifesting as a severe thoracic dystrophy, rhizoacromelic type of micromelia, postaxial polydactyly, and genital anomalies in the males. Verma et al. (1975) suggested that the disorder in these sibs represented a distinct entity similar to the disorder reported by Saldino and Noonan (1972).

Naumoff et al. (1977) described what they considered to be a novel form of short rib-polydactyly syndrome (SRPS III) in 3 patients who died perinatally of asphyxia due to thoracic narrowing and found 3 possibly identical cases in the literature. Their patients 1 and 2 were brother and sister. They suggested that the disorder reported by Verma et al. (1975) may be the same as that in their patient.

Yang et al. (1980) reported a case of SRPS III with previously undescribed cytoplasmic inclusion bodies that were PAS-positive and diastase-resistant. They found that cloacal developmental abnormalities, which are invariably present in patients with SRPS I, are rare in SRPS III (1 in 13 cases).

Sillence (1980) suggested that the claimed differences between SRPS types II and III are probably due to variability and not to heterogeneity, a view in which Spranger (1981) concurred.

Bernstein et al. (1985) presented 4 cases of short rib-polydactyly syndrome from 3 nonconsanguineous families. The findings were most consistent with type III. They raised the question of allelism of the 3 types, being particularly impressed with the phenotypic overlap of SRPS I and SRPS III. All 4 of their cases showed anomalous sexual development. In spite of testicular differentiation in all 4 and a 46,XY karyotype in the 2 on whom chromosome studies were done, 2 infants were phenotypically female and 2 had ambiguous genitalia.

Through the Spanish collaborative study of congenital malformations, Martinez-Frias et al. (1993) identified 2 unrelated infants with short rib-polydactyly syndrome and clinical/radiologic features overlapping the 4 established forms of lethal SRPS. One of the infants had one of the most radiologically severe SRPS published to date. Martinez-Frias et al. (1993) raised again the question of whether this group of disorders represents a continuous spectrum rather than separate entities. Sarafoglou et al. (1999) also reported a fetus with radiologic features of the 4 established types, supporting the hypothesis that the different subtypes are not single entities, but part of a continuous spectrum with variable expressivity.

Wu et al. (1995) described a family in which 3 consecutive conceptions resulted in 4 infants with short rib-polydactyly syndrome. One was a twin conception. The condition was identified in the second and third pregnancies by prenatal ultrasound studies. Flat face, hypoplastic thorax, short limbs and ribs, polydactyly, absence of penis, and death soon after birth were noted in the first affected male baby. The affected female twins had the same characteristics, though milder. The last male baby was also severely affected, suggesting that chromosomal sex may be a modifying factor. Wu et al. (1995) suggested that the first and fourth cases most resembled SRPS III, whereas the twins resembled the type described by Marec et al. (1973) (SRPS I) in 2 pairs of sibs.

From clinicopathologic investigation of 8 patients with asphyxiating thoracic dystrophy, Yang et al. (1987) suggested the existence of 2 types of ATD: type 1 was characterized by the presence of radiologically irregular metaphyseal ends and histopathologic ally irregular cartilage-bone junction with patchy distribution of the physeal zone of hypertrophy; type 2 showed radiologically smooth metaphyseal ends and histopathologically diffusely retarded and disorganized physes with smooth cartilage-bone junctions. The authors were impressed with the similarities between type 1 ATD and short rib-polydactyly syndrome type III.

Ho et al. (2000) reported a family with 2 brothers affected with mild Jeune syndrome, and a stillborn male infant, the product of a marriage between the paternal first cousin and a maternal aunt of the 2 boys, with lethal SRPS type III. The authors suggested that these conditions may be variants of a single disorder. They proposed that the intrafamilial variability may reflect the effects of modifying loci on gene expression.

Through a study to identify the molecular basis of asphyxiating thoracic dystrophy and short rib-polydactyly syndrome type III, Dagoneau et al. (2009) identified 3 families with ATD and 2 families with SRPS3. Criteria for inclusion in the study were short ribs and a restricted thoracic cage; trident acetabular roof; small hands and feet; and shortening of the long bones. The 3 families with ATD were a large consanguineous Moroccan family and 2 small nonconsanguineous families from France. The 3 ATD families included 5 cases. In the first family, 1 child died of respiratory distress, and pregnancy of her aunt was terminated at 28 weeks' gestation for severe narrowing of the thorax. In the second family, 2 pregnancies were terminated for severe narrowing of the thorax. In the third family the affected child was 19 years old at the time of the report; no eye, liver, or kidney manifestations were detected. In the 2 SRPS3 families, the diagnosis was made before 20 weeks of gestation in 4 fetuses and the pregnancies were terminated.

Schmidts et al. (2013) reported 29 patients from 19 families with ATD confirmed by genetic analysis. The clinical course was dominated by abnormal bone development with a small thorax due to reduced rib length, handlebar clavicles, scoliosis, and shortened long bones, particularly femurs. There was wide variability in rib shortening and a variable degree of respiratory impairment, even within the same family. Some patients had brachydactyly with cone-shaped epiphyses, but only 1 patient exhibited polydactyly, consisting of unilateral postaxial polydactyly of the hand. Short stature with variable shortening of the limbs and some bowing was often found in early childhood, but most patients reached normal height by adolescence or adulthood. Mild renal, retinal, and liver abnormalities were only rarely observed in 1 or 2 patients overall, so extraskeletal manifestations were essentially absent.

Badiner et al. (2017) reported 3 patients with a severe phenotype thought to be most consistent with short-rib polydactyly type I. All 3 patients presented in utero. Findings included narrow thorax, polydactyly, abdominal ascites, and hydrops fetalis. In addition, cardiovascular, gastrointestinal, renal, and genital anomalies were identified. Craniofacial abnormalities included cleft lip and palate in 2 individuals. Radiographic findings included severely delayed ossification of the calvarium, metacarpals, metatarsals, and all phalanges. Hypoplastic vertebrae, mild platyspondyly with severely widened intervertebral disc spaces, and coronal clefts were observed. Micromelia with bilateral shortening of all long bones in upper and lower extremities was also seen. Only 11 ribs were visible on x-ray, all of which were horizontal and extremely short. Ilia had decreased height and increased width. Lower extremities showed ovoid tibiae and underdeveloped or absent fibulae.

Inheritance

The transmission pattern of ATD/SRPS in the families reported by Dagoneau et al. (2009) and Schmidts et al. (2013) was consistent with autosomal recessive inheritance.

Diagnosis

Prenatal Diagnosis

Meizner and Barnhard (1995) reported diagnosis of SRPS III at 20 weeks' gestation during routine ultrasonographic screening in a 21-year-old Bedouin woman. Widened humeral metaphyses with marginal spurs, postaxial polydactyly and shortened ribs were demonstrated. The authors suggested that polycystic kidneys and pointed metaphyses characterize SRPS I; cleft lip/palate, polycystic kidneys, and disproportionately short tibia characterize SRPS II; and acromesomelia and congenital heart disease characterize the Ellis-van Creveld syndrome.

Mapping

Using linkage and microsatellite marker analysis in a large consanguineous Moroccan family, Dagoneau et al. (2009) mapped the ATD phenotype to chromosome 11q14.3-q23.1, in a 20.4-Mb region bounded centromerically by D11S4175 and telomerically by D11S1893. The region contains 85 genes.

Molecular Genetics

Among the genes in the 20.4-Mb critical region for asphyxiating thoracic dystrophy, Dagoneau et al. (2009) considered DYNC2H1 a good candidate gene because it encodes a subunit of a cytoplasmic dynein complex. The authors sequenced all 90 exons of the DYNC2H1 gene and identified 2 homozygous missense mutations in 2 affected Moroccan children (M1991L, 603297.0001 and M3762V, 603297.0002). The mutations cosegregated with the disease and were not identified in 210 ethnically matched control chromosomes. Dagoneau et al. (2009) identified 4 other missense and nonsense mutations (603297.0003-603297.0006) in compound heterozygosity in 2 other families, both nonconsanguineous, with a clinical diagnosis of ATD. In 2 families in which members had a clinical diagnosis of short rib polydactyly type III, Dagoneau et al. (2009) identified compound heterozygous mutations in the DYNC2H1 gene (603297.0012-603297.0014). Dagoneau et al. (2009) concluded that ATD and SRPS III are variants of a single disorder belonging to the ciliopathy group.

Merrill et al. (2009) identified homozygosity or compound heterozygosity for missense or nonsense mutations in the DYNC2H1 gene (603297.0007-603297.0011) in patients with a clinical diagnosis of short rib-polydactyly type III.

In a proband from a nonconsanguineous family with a clinical diagnosis of short-rib polydactyly type II, or Majewski syndrome, Thiel et al. (2011) identified heterozygosity for a missense mutation in the DYNC2H1 gene (603297.0016) and heterozygosity for a missense mutation in the NEK1 gene (604588.0003). No second mutation was found in either gene and each parent was heterozygous for one of the mutations; thus, this patient appeared to represent a digenic biallelic phenotype.

El Hokayem et al. (2012) analyzed the DYNC2H1 gene in 7 unrelated cases diagnosed with short-rib polydactyly type II, all of which were either terminated pregnancies or cases of neonatal death and in which mutation in the NEK1 gene (604588) had been excluded, and identified compound heterozygous DYNC2H1 mutations in 4 of the families (see, e.g., 604588.0017-604588.0020).

Using a combination of SNP mapping, exome sequencing, and Sanger sequencing, Schmidts et al. (2013) identified 34 DYNC2H1 mutations (see, e.g., D3015G, 603297.0004 and I1240T, 603297.0005) in 29 (41%) of 71 patients from 19 (33%) of 57 families with a clinical diagnosis of ATD. Most of the mutations were private, occurring in only 1 family. The variants included 13 terminating mutations and 21 missense mutations distributed across the gene, with some clustering of the missense mutations in functional domains. All mutations occurred in homozygous or compound heterozygous state, and no patients had 2 truncating mutations, suggesting that the human phenotype is at least partly hypomorphic. Two patients carried 3 pathogenic mutations in the DYNC2H1 gene. No functional studies were performed. Patient fibroblasts showed defects in retrograde intraflagellar transport (IFT), as demonstrated by accumulation of anterograde proteins IFT57 (606621) and IFT88 (600595) in the ciliary tips. However, the extent of this cellular defect varied significantly among patients. Ciliary length and number were similar to controls. The patients were mainly of northern European or Turkish origin, and the findings indicated that DYNC2H1 mutations are the most frequent overall cause of ATD.

Using exome sequencing, Badiner et al. (2017) identified 3 patients with a severe phenotype thought to be most consistent with short-rib polydactyly type I. All 3 patients were compound heterozygous for mutations in DYNC2H1; 5 of the mutations were missense changes at highly conserved residues, and 1 was a null mutation. All of the mutations were rare, including 4 that had not previously been reported in public sequence databases or in patients with short-rib polydactyly.

History

The short rib-polydactyly syndromes (SRPS) were defined as a group of autosomal recessive lethal skeletal dysplasias characterized by markedly short ribs, short limbs, polydactyly, and multiple anomalies of major organs, including heart, intestines, genitalia, kidney, liver, and pancreas. There is phenotypic overlap in various forms of SRPS (summary by Elcioglu and Hall, 2002). Five types had been distinguished: SRPS I (Saldino-Noonan type); SRPS II (Majewski type), SRPS III (Verma-Naumoff type), SRPS IV (Beemer-Langer type), and SRPS V (Elcioglu and Hall, 2002; Mill et al., 2011).

Because of speculation that ATD and SRPS type III represent the severe end of the Ellis-van Creveld syndrome spectrum, Krakow et al. (2000) performed linkage analysis using markers from the EVC region on 4p in 7 families manifesting either ATD or SRPS type III. In 2 of the families, 1 segregating ATD and the other SRPS, linkage of the phenotype to the EVC region was excluded.

The question of SRPS III being due to disruption of a gene in the 4p16 region where EVC maps was raised by Urioste et al. (1994), but was excluded in one family with SRPS III by linkage analysis (Krakow et al., 2000). Takamine et al. (2004) sequenced all 21 coding exons and flanking intron sequences of the EVC1 gene (604831) in 10 unrelated cases of SRPS III and found no mutations interpreted as pathologic.