Jürgen W. Spranger

The type II collagenopathies: a spectrum of chondrodysplasias.

With the application of molecular techniques the aetiopathogenesis of skeletal dysplasias is gradually elucidated. Recent advances show that some bone dysplasias result from defects in the biosynthesis of type II (cartilage) collagen. Clinical entities caused by mutations in the COL2A1 gene coding for type II collagen comprise achondrogenesis II, hypochondrogenesis, spondylo-epiphyseal dysplasia congenita, Kniest dysplasia, Stickler arthro-opthalmopathy and mild dominant spondyloarthropathy. The mutations are expressed in the heterozygous state, and inheritance of type II collagenopathies is autosomal dominant. The wide range of clinical manifestations is not well understood but characterization of the basic defect may provide clues to establish specific genotype-phenotype correlations.

Mucolipidosis I: Increased sialic acid content and deficiency of an α-N-acetylneuraminidase in cultured fibroblasts

Abstract Extracts of fibroblasts derived from a patient with mucolipidosis I exhibited a fivefold increase in sialic acid content as compared to those of normal cells. About 80% of this sialic acid was linked to other molecules. Using neuraminlactose as a substrate, mucolipidosis I fibroblasts were found to be severely deficient in an “acid” α-N-acetylneuraminidase. Since other lysosomal hydrolase activities were normal, we hypothesize that the basic metabolic lesion in mucolipidosis I lies in a defective degradation of sialic acid-containing compounds due to the genetic deficiency of a neuraminidase.

Malformations in newborn: results based on 30940 infants and fetuses from the Mainz congenital birth defect monitoring system (1990-1998)

Abstract Prevalence rates of birth defects in the Federal Republic of Germany are informative to assess the general background risk of having a child with a birth defect. They provide basic figures to determine temporal and regional prevalence trends, to evaluate and initiate preventive measures and to initiate research projects. To avoid observer, definition and collection bias, active monitoring systems are required. Data collected in the active monitoring system of the Mainz Birth Defects Registry are presented. From 1990–1998, 30940 livebirths, stillbirths and abortions underwent standardized physical and sonographic examinations. Anamnestic data were collected from prenatal care records, maternity files and hospital records. Major malformations were diagnosed in 2144 (6.9%) and mild errors of morphogenesis in 11104 (35.8%) of all infants. Risk factors associated with the occurrence of major malformations were identified by comparing anamnestic data from infants with and without major malformations. Using multivariate regression models, statistically significant associations were established for 9 risk factors. Causally related risk factors were parents or siblings with malformations, parental consanguinity, more than 3 minor errors of morphogenesis in the proband, maternal diabetes mellitus and ingestion of antiallergic drugs in the first trimester of pregnancy. Conjunctional risk factors were polyhydramnios, oligohydramnios and gestational age <32 weeks at birth. Using these risk factors, populations at risk for the occurrence of major malformation can be identified.

Structural and Functional Mutations of the Perlecan Gene Cause Schwartz-Jampel Syndrome, with Myotonic Myopathy and Chondrodysplasia

Perlecan, a large heparan sulfate proteoglycan, is a component of the basement membrane and other extracellular matrices and has been implicated in multiple biological functions. Mutations in the perlecan gene (HSPG2) cause two classes of skeletal disorders: the relatively mild Schwartz-Jampel syndrome (SJS) and severe neonatal lethal dyssegmental dysplasia, Silverman-Handmaker type (DDSH). SJS is an autosomal recessive skeletal dysplasia characterized by varying degrees of myotonia and chondrodysplasia, and patients with SJS survive. The molecular mechanism underlying the chondrodystrophic myotonia phenotype of SJS is unknown. In the present report, we identify five different mutations that resulted in various forms of perlecan in three unrelated patients with SJS. Heterozygous mutations in two patients with SJS either produced truncated perlecan that lacked domain V or significantly reduced levels of wild-type perlecan. The third patient had a homozygous 7-kb deletion that resulted in reduced amounts of nearly full-length perlecan. Unlike DDSH, the SJS mutations result in different forms of perlecan in reduced levels that are secreted to the extracellular matrix and are likely partially functional. These findings suggest that perlecan has an important role in neuromuscular function and cartilage formation, and they define the molecular basis involved in the difference in the phenotypic severity between DDSH and SJS.

Manifestations and treatment of Schimke immuno-osseous dysplasia: 14 new cases and a review of the literature.

Abstract Schimke immuno-osseous dysplasia (SIOD) is a rare autosomal recessive spondylo-epiphyseal dysplasia. The characteristic features of SIOD include 1) short stature with hyperpigmented macules and an unusual facies, 2) proteinuria with progressive renal failure, 3) lymphopenia with recurrent infections, and 4) cerebral ischaemia. Although 25 patients have been reported with this disorder, the clinical course and phenotype of SIOD are not well characterized. This report summarizes the clinical findings, course and treatment of reported patients and includes 14 additional patients with SIOD. We emphasize the high incidence of cerebral ischaemia and ocular abnormalities, define the high incidence of thyroid dysfunction and blood cytopenia, and confirm the absence of effective and durable medical therapies. Conclusion Schimke immuno-osseous dysplasia is a multi-system autosomal recessive disorder with variable expression that affects the skeletal, renal, immune, vascular, and haematopoietic systems. Medical therapy is limited especially for more severely affected individuals.

Recessively inherited multiple epiphyseal dysplasia with normal stature, club foot, and double layered patella caused by a DTDST mutation

We have observed over 25 different mutations in the diastrophic dysplasia sulphate transporter gene (DTDST) in association with the recessive disorders achondrogenesis 1B, atelosteogenesis 2, and diastrophic dysplasia. The c862t (R279W) transition is the most common mutation in non-Finnish patients, but in these disorders it is usually combined with otherDTDST mutations. We had not seen a case of homozygosity for c862t (R279W) until we analysed DNA from a 36 year old male with tall-normal stature (180 cm) who asked for genetic counselling for suspected multiple epiphyseal dysplasia. He was treated for club foot and hip dysplasia at birth. Skeletal changes consistent with multiple epiphyseal dysplasia, with the peculiar finding of a double layered patella, were recognised during childhood. Cleft palate, swelling of the ear pinna, and hitch hiker thumb were absent. He was found to be homozygous, and both healthy parents heterozygous, for the R279W mutation in DTDST, and his fibroblasts showed a sulphate incorporation defect typical of DTDST disorders. Counselling was given for a recessive disorder, thereby considerably reducing the probability of affected offspring.  Multiple epiphyseal dysplasia is more frequently caused by dominant mutations in the COMP (EDM1, McKusick 132400) and COL9A2 genes (EDM2, McKusick 600204). A few other patients and families with features similar to our proband have been described previously and considered to have autosomal recessive MED (EDM4, McKusick 226900). This observation confirms the existence of this entity and assigns it to the phenotypic spectrum associated with mutations at theDTDST locus.

The lethal osteochondrodysplasias.

Achondrogenesis was first described in 1936 by Parenti (1936). Lethal cases of osteogenesis imperfecta have been known since Vrolik’s (1849) description. Achondroplasia (formerly chondrodystrophy) was the only other diagnosis for all other dwarfed newborns until thanatophoric dysplasia was recognized as a separate entity (Maroteaux et al., 1967).

Severely Incapacitating Mutations in Patients with Extreme Short Stature Identify RNA-Processing Endoribonuclease RMRP as an Essential Cell Growth Regulator

The growth of an individual is deeply influenced by the regulation of cell growth and division, both of which also contribute to a wide variety of pathological conditions, including cancer, diabetes, and inflammation. To identify a major regulator of human growth, we performed positional cloning in an autosomal recessive type of profound short stature, anauxetic dysplasia. Homozygosity mapping led to the identification of novel mutations in the RMRP gene, which was previously known to cause two milder types of short stature with susceptibility to cancer, cartilage hair hypoplasia, and metaphyseal dysplasia without hypotrichosis. We show that different RMRP gene mutations lead to decreased cell growth by impairing ribosomal assembly and by altering cyclin-dependent cell cycle regulation. Clinical heterogeneity is explained by a correlation between the level and type of functional impairment in vitro and the severity of short stature or predisposition to cancer. Whereas the cartilage hair hypoplasia founder mutation affects both pathways intermediately, anauxetic dysplasia mutations do not affect B-cyclin messenger RNA (mRNA) levels but do severely incapacitate ribosomal assembly via defective endonucleolytic cleavage. Anauxetic dysplasia mutations thus lead to poor processing of ribosomal RNA while allowing normal mRNA processing and, therefore, genetically separate the different functions of RNase MRP.

Spondyloepiphyseal Dysplasia Congenita

In 29 patients spondyloepiphyseal dysplasia (SED) congenita, an heritable bone dysplasia, was manifest at birth with small stature and retarded ossification of vertebral bodies, pelvis, and extremities. In later childhood characteristic changes include flattening and dysplasia of vertebral bodies, odontoid hypoplasia, pelvic dysplasia, and underossification of the femoral head and neck with varus deformity. Shortened long tubular bones exhibit varied degrees of epiphyseal and metaphyseal changes. Myopia and retinal detachment are important clinical findings in many patients. SED congenita is differentiated from Morquios disease by roentgen features, its dominant mode of inheritance, lack of corneal clouding, and keratosulfaturia.

Vitamin K deficiency embryopathy: A phenocopy of the warfarin embryopathy due to a disorder of embryonic vitamin K metabolism

Three unrelated infants presented with radiographic punctate calcifications, nasal hypoplasia, and abnormalities of the spine. Additional anomalies included cupped ears in 2 patients and one each with Dandy-Walker malformation with hydrocephaly, congenital cataracts, and peripheral pulmonary artery stenosis. The mothers of these 3 patients had chronic conditions associated with intestinal malabsorption requiring total parenteral nutrition for varying periods of time. The underlying causes of malabsorption were celiac disease, short bowel syndrome secondary to surgical resection, and jejuno-ileal bypass, respectively. Bleeding diathesis occurred in one mother requiring vitamin K supplementation during the second and third trimesters of pregnancy. We speculate that the chondrodysplasia punctata and other abnormalities in these children were caused by an acquired maternal vitamin K deficiency manifested during early pregnancy. However, the involvement of other vitamin deficiencies cannot be excluded. Thus, vitamin K deficiency of the embryo secondary to maternal malabsorption appears to be a third vitamin K-related mechanism leading to chondrodysplasia punctata in addition to warfarin embryopathy and epoxide reductase deficiency (pseudo-warfarin embryopathy).