Tuninetti Valentina
Pagotto Lara
DEFINITION
Greenberg skeletal dysplasia, also called hydrops-ectopic calcification-“moth-eaten” (HEM), is an autosomal recessive chondrodystrophy with letal course, characterized by fetal hydrops, short limbs, and abnormal chondro-osseous calcification.
It is related to a deficiency of the cholesterol biosynthetic enzyme 3b-hydroxysterol D14-reductase.
CASES’ SUMMARY
The initial case described by Greenberg et al. [1988] was stillborn with hydrops fetalis, while the second sibling of the same consanguineous parents was discovered by ultrasound examination at 20 weeks. This pattern of hydrops fetalis with ectopic calcifications and moth-eaten short-limbed skeletal dysplasia was also described by several studies: Spranger and Maroteaux [1990], Chitayat et al. [1993], Horn et al. [2000], and Madazli et al. [2001], Trajkovski et al. [2002].
The association of fetal hydrops with irregular (ectopic) calcification `moth-eaten' skeletal dysplasia, first described by Greenberg et al. (1988), was given the acronym HEM (hydrops ectopic calcification `moth-eaten' skeletal dysplasia) by Tayby and Lachman (1990). Unfortunately, the term ectopic calcification suggests calcium deposits in extraskeletal locations and its use should be restricted. Additionally,there were no calcifications, despite of bones, in the cases which were reported previously in the literature (Greenberg et al., 1988; Spranger and Maroteaux,1990; Chitayat et al., 1993). The clinical and morphological characteristics of the well-documented cases are summarized in Table 1. It can be seen that the phenotypical appearance may occur early in pregnancy, as seen in the case of Chitayat et al. (1993).
However phenotypic expression may vary between cases. Sharony et al. (1993) had mentioned one case of Greenberg dysplasia (GBD) in their study of 226 fetuses and stillbirths referred for suspected skeletal dysplasia. Unfortunately, no further description of this case was given.
Several LOC (lethal osteochondrodysplasia) could be accompanied by non-immunologic fetal hydrops (van Maldergem et al., 1992) and should be considered at differential diagnosis.
As pointed out by Sharony et al. (1993), an exact prenatal diagnosis of skeletal dysplasia is almost impossible, but LOC can be suspected on antenatal sonography. Pattern of multicentric ossification as seen in cases of GBD has been described in stillbirths with dappled diaphysis dysplasia (Carty et al., 1989), however the osseous changes are more severe than in GBD (Spranger and Maroteaux, 1990).
Cystic hygromas and generalised fetal hydrops have been seen in other LOC such as achondroplasia, achondrogenesis type II and in dappled diaphysis dysplasia, respectively.
In GBD only the case of Chitayat et al. (1993) showed additional skeletal abnormalities (See Table 1).
SYMPTOMS
There are no symptoms related to Greenberg Dysplasia because it is a fetal disease. It is identified by ultrasound and radiography.
GENETIC AND BIOCHEMICAL BACKGROUND
This disease shows elevated levels of cholesta-8,14-dien-3b-ol, compatible with a deficiency of the cholesterol biosynthetic enzyme 3b-hydroxysterol D14-reductase. The synthesis of cholesterol from lanosterol requires removal of the 14a-methyl group from either lanosterol or dihydrolanosterol which results in the formation of a C14–C15 double bond. This C14–C15 double bond must subsequently be reduced by a sterol D14-reductase. (see Figure 4)
Figure 4: Biochemical pathway from lanosterol to cholesterol
Autosomal recessive HEM/Greenberg skeletal dysplasia is caused by 3 beta-hydroxysterol delta 14-reductase deficiency due to mutations in the lamin B receptor gene, 2003
Two different genes have been reported to encode human sterol D14-reductases: LBR (GenBank accession number L25932–L25941) at 1q42 and TM7SF2,also noun as DHCR14 (GenBank accession number AF096303) at 11q13. LBR encodes the lamin B receptor, a 70.4-kDa protein of the inner nuclear membrane that contains an N-terminal lamin B/ DNA-binding domain of ∼200 amino acids followed by a C-terminal sterol reductase-like domain of ∼450 amino acids (Holmer et al. 1998), which exhibits sterol D14- reductase activity when expressed in yeast (Silve et al.1998). TM7SF2 encodes a sterol reductase of 46.4 kDa located in the endoplasmic reticulum (ER) membrane (Holmer et al. 1998), which exhibits sterol D14-reductase activity when overexpressed in COS-7 cells (Roberti et al. 2002).
These genes identified a homozygous 1599–1605TCTTCTArCTAGAAG substitution in exon 13 of the LBR gene encoding the lamin B receptor, which results in a truncated protein. Functional complementation of the HEM cells by transfection with control LBR cDNA confirmed that LBR encoded the defective sterol D14-reductase. Mutations in LBR recently have been reported also to cause Pelger-Hue¨t anomaly, an autosomal dominant trait characterized by hypolobulated nuclei and abnormal chromatin structure in granulocytes. The fact that the healthy mother of the fetus showed hypolobulated nuclei in 60% of her granulocytes confirms that classic Pelger-Hue¨t anomaly represents the heterozygous state of 3b-hydroxysterol D14-reductase deficiency.
LBR is a bifunctional protein with both a lamin B binding and a sterol D14-reductase domain. It previously has been proposed that LBR is the primary sterol D14-reductase and that HEM dysplasia and ichthyosis are inborn errors of cholesterol synthesis. However, DHCR14 also encodes a sterol D14-reductase and could provide enzymatic redundancy with respect to cholesterol synthesis. Although only a minor sterol abnormality has been reported, it has been proposed that LBR is the primary sterolΔ14-reductase and that impaired sterol Δ14-reduction underlies HEM dysplasia. However, DHCR14 also encodes a sterol Δ14-reductase.
To test the hypothesis that LBR and DHCR14 are redundant sterol Δ14-reductases, we obtained ichthyosis mice (Lbr−/−) and disrupted Dhcr14. Dhcr14−/− mice are phenotypically normal. We found no sterol abnormalities in either Lbr−/− or Dhcr14−/− tissues at 1 and 21 days of age. We then bred the mice to obtain compound mutant mice. Lbr−/−:Dhcr14−/− and Lbr−/−:Dhcr14+/− died in utero. Lbr+/−:Dhcr14−/− mice appeared normal at birth but, by 10 days of age, were growth-retarded and neurologically abnormal (with ataxia and tremors) and, consistent with a demyelinating process, evidenced vacuolation and swelling of the myelin sheaths in the spinal cord upon pathological evaluation. We observed neither vacuolation nor swelling of the myelin sheaths in either Lbr−/− or Dhcr14−/−mice. In contrast to Lbr−/− mice, Lbr+/−:Dhcr14−/− mice had normal skin and did not display the Pelger-Huët anomaly. Peripheral tissue sterols were normal in all three mutant mice, although we found significantly elevated levels (50% of total sterols) of cholesta-8,14-dien-3β-ol and cholesta-8,14,24-trien-3β-ol in brain tissue from 10-day-old Lbr+/−:Dhcr14−/− mice. In contrast, we observed relatively small transient elevations of Δ14-sterols in Lbr−/− and Dhcr14Δ4-7/Δ4-7 brain tissue. Our data support the idea that HEM dysplasia and ichthyosis result from impaired lamin B receptor function rather than from impaired sterol Δ14-reduction. Impaired sterol Δ14-reduction gives rise to a novel murine phenotype for which a corresponding human disorder has yet to be identified.
HEM dysplasia and ichthyosis are likely laminopathies and not due to 3beta-hydroxysterol Delta14-reductase deficiency,2007
Congenital abnormalities reported in Pelger-Huët homozygosity as compared to Greenberg/HEM dysplasia: highly variable expression of allelic phenotypes,2003
DIAGNOSIS
Greenberg dysplasia has distinct radiological features. The most prominent radiological sign is the moth-eaten appearance of the long bones with bizarre ossification centers.
Additionally, long bones are markedly shortened and platyspondyly is found with unusual ossification centers.
CLINICAL REPORT
A 23-year-old woman para2 came for a regular fetal ultrasound checkup in the 22nd week of gestation. The father was 30 years old. Consanguinity was denied. Both parents had Macedonian ethnic origin. No blood incompatibility was found between the parents. The first pregnancy ended with spontaneous abortion at home of a female fetus in the 22nd–24th week of gestation. The parents were not able to give any other information about the first pregnancy and the delivered fetus. The ultrasound of the second fetus showed polyhydramnios, fetal hydrops, cystic neck hygroma, severe short limbs, short stature, platyspondyly, and a barrel-shaped chest.
The pregnancy was terminated at 23rd week of gestation. The fetus was male (Fig. 2). Severe hydrops fetalis,large head with cystic hygroma, and rhizomelic and mezomelic shortness of long bones were found.Nohematopoetic bone marrow was found in the long bones. Marked extramedullary liver hematopoesis was present.
The brain, heart, lungs, kidneys, gonads, external genitalia were normal. The fetus weighted 330 g (normal, 450_118 g). The head circumference was 24 cm (normal, 20_1.2 cm), chest circumference 14 cm (18_3.0 cm), crown-heel length was 23.5 cm (28.7_ 3.3 cm), the crown-rump length 20.5 cm (20.6_2.3 cm), foot 3 cm (3.9_1.5 cm).
Figura 5. Fetus at 23 weeks of gestation: severe hydrops fetails, large head, cystic hygroma, and rhizomelic and mezomelic shortness of long bones. The midface hypoplasia and the prominent orbital arches render a bizzarre highbrow appearance.
Greenberg dysplasia: first reported case with additional non-skeletal malformations and without consanguinity, 2000
RADIOGRAPHYC FINDINGS
A combination of deficient ossification and the presence of extra ossification centers was found (Fig. 3). The membranous part of the skull was sparsely ossified while the base of the skull was dense. The nasal bridge was depressed. Both the maxilla and the mandible were small. This midface hypoplasia combined with prominent orbital arches gave a bizarre facial highbrow appearance. The chest was narrow, barrel-shaped, clavicles were elongated, ribs were short, hypoplastic, and of similar length. The rib ends were broad and spur-like calcified. Extra ossification centers were found in the larynx, trachea, and vertebral bodies. A severe platyspondyly was noted, as well as the presence of dense bone in the spinous processes. On the other hand, the vertebral pedicles and lamina were maldeveloped.
The iliac wings were ragged with calcification of their lower parts. The sacrum was horizontally placed. Metaphyses were cupped and moth eaten. The diaphysis were severely shortened and curved. Some of the epiphyses had prominent irregular calcification. Hands were ulnarly deviated. Rudimentary calcaneus and a spot-like talus were noted.
Figura 6. Skeletal films, LL (A) and AP (B) view. The membranous part of the skull is sparsely ossified, chest is barrel-shaped, ribs ends are spur-like calcified. Severe platyspondyly, ossification of spinous processes. Methaphyses are moth-eaten.
HYSTOPATHOLOGY
Specimens of ribs and long bones were analyzed after standard sections and staining with a variety of stains.
The most prominent histopathologic finding was severe disorganization. No normal cartilage column formation was present and there was abrupt transition from cartilage to abnormal bone. In addition, there was marked irregularity of growth plates with in some segments mesenchymal-like tissue between bone and cartilage. Extra ossification centers on inappropriate sites with abnormal, hypercellular bone were also observed.
THERAPY
Actually there are no treatments but in the future is possible, using molecular biology, acting toward Greenberg responsible genes.
