Multiple epiphyseal dysplasia: clinical and radiographic features, differential diagnosis and molecular basis

Best Practice & Research Clinical Rheumatology Vol. 22, No. 1, pp. 19–32, 2008 doi:10.1016/j.berh.2007.11.009 available online at http://www.sciencedirect.com

2 Multiple epiphyseal dysplasia: clinical and radiographic features, differential diagnosis and molecular basis Sheila Unger Staff Geneticist and ESDN Coordinator Department of Paediatrics and Institute of Human Genetics, University of Freiburg, Freiburg, Germany

Luisa Bonafe´ Head Division of Molecular Paediatrics, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland

Andrea Superti-Furga * Director and Chair Department of Paediatrics, University of Freiburg, Freiburg, Germany

Multiple epiphyseal dysplasia is one of the more common skeletal dysplasias but it can still be difficult to diagnose. The presenting signs are often rheumatological (‘joint pain’) or neurological (‘myopathy’) in nature, and the cardinal feature of skeletal dysplasia (short stature) may not be present. A radiographic skeletal survey is necessary to delineate the pattern of generalized delayed epiphyseal ossification and changes in epiphyseal contour. Once the diagnosis of multiple epiphyseal dysplasia has been established, careful examination of the radiographs can help to determine which genes should be analysed. Mutations in at least six different genes can cause multiple epiphyseal dysplasia, and it can be either dominant or recessive. Molecular diagnosis is important for accurate prognosis and genetic counselling. Key words: multiple epiphyseal dysplasia; COMP; COL9A1; COL9A2; COL9A3; MATN3; DTDST; bone age; delayed epiphyseal ossification.

* Corresponding author. Centre for Paediatrics and Adolescent Medicine, Freiburg University Hospital, Mathildenstr. 1, D-79106 Freiburg, Germany, Tel.: þ49 761 270 4305; Fax: þ49 761 270 4454. E-mail address: [email protected] (A. Superti-Furga). 1521-6942/$ - see front matter ª 2007 Published by Elsevier Ltd.

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Multiple epiphyseal dysplasia (MED) is a mild form of skeletal dysplasia. Genetically, it is fairly heterogeneous with mutations in COMP, DTDST (SLC26A2), MATN3, COL9A1, COL9A2 and COL9A3 capable of producing the clinical picture of MED. While fullblown, severe phenotypic expressions of mutations in genes such as COMP, DTDST (SLC26A2) and MATN3 produce quite distinct phenotypes, less severe mutations tend to blend into the relatively mild phenotype of MED. Nonetheless, the distinct genetic forms of MED can usually be distinguished by virtue of subtle clinical and radiographic signs and by their mode of inheritance. Clinically, the disease manifests with joint disease and sometimes with reduced growth. Radiographically, there is both a delay in ossification (‘maturation’) of epiphyses and changes in their shape. Originally, MED was subdivided into ‘Fairbanks’ and ‘Ribbing’ forms but this has not proved useful. COMMON CLINICAL FEATURES As a rule, the MED phenotype is not recognizable at birth or during the first 1–2 years of life. A newborn destined to develop MED shows normal length and normal body proportions. One exception to this rule is the presence of club foot at birth in some cases, with recessive MED caused by mutations in DTDST.1 A common presenting sign is joint pain affecting the hip and knee joints, occurring, at least initially, after physical exercise. During childhood, progressive deviation from the normal growth curve can occur, resulting in mild to moderate short stature (around or slightly below the third percentile) by the age of 5–6 years. However, there are many examples of adults with MED of normal stature.2 Muscular hypotonia is frequent in young children with MED caused by COMP mutations (sometimes even frank myopathy).3 Thus, a typical history would be that of a child who was clinically normal at birth, but with some delay in motor development, and who starts to complain about joint pain after a long walk, after a ball game or after physical exercise. Paediatric examination may reveal a deviation of the growth curve. At that time, a diagnosis of MED in the child may be supported by a family history of similar symptoms in one of his parents or older siblings, or of a history of chronic joint disease, sometimes leading to total hip arthroplasty at a relatively early age, in one of his parents or grandparents. Changes in the femoral heads occurring in school-age children with MED may resemble those seen in ‘idiopathic’ necrosis of the femoral head (Legg-Calve´-Perthes disease). While the majority of cases of Perthes disease are limited to one side and are rarely (as far as is known) the expression of a generalized skeletal anomaly, in cases where Perthes disease is familial, bilateral or associated with short stature, a clinical examination and a radiographic skeletal survey should be performed to rule out MED. As the mildest phenotype of skeletal dysplasia, MED affects the epiphyses of tubular bones, including metacarpals, metatarsals and phalanges; the metaphyses and vertebral bodies are only affected slightly or not at all. The effect on the epiphyses manifests on radiographs as a maturational delay. The pattern of delay and the changes in shape are helpful in distinguishing the different genetic forms of MED. The type of MED needs to be determined before providing the patient and their family with precise genetic counselling. Table 1 gives an overview of the distinctive features of the various forms of MED. In the following sections, some of the features that are useful in the differential diagnosis between the various forms of MED will be presented. The MED forms are discussed in order of decreasing incidence.

Table 1. Overview of the different forms of multiple epiphyseal dysplasia (MED) and their distinctive features.

MIM number Gene Inheritance Relative frequency

EDM1 (COMP-MED)

EDM4 (rMED)

EDM5 (MATN3-MED)

EDM2

EDM3

EDM6

132400

226900

607078

600204

600969

(see 120210)

COMP AD þþþ

DTDST (SCL26A2) AR þþ

MATN3 AD þ

COL9A2 AD Rare (but may be under reported)

COL9A3 AD Rare (but may be under reported)

COL9A1 AD Very rare (one single family reported)

Knee epiphyses more affected than proximal femoral epiphyses

Knee epiphyses more affected than proximal femoral epiphyses

Distinctive Muscular hypotonia, pseudoclinical myopathy, joint laxity, mild features genu vara Distinctive radiographic features Hand Carpal bones more delayed than phalangeal epiphyses; ragged carpal bones, small, rounded phalangeal epiphyses

Proximal femoral epiphyses round and small

Knee

Small epiphyses with lateral thinning, additional ossification centres with ‘glacier crevice’ sign before puberty

Phalangeal epiphyses delayed, but maturation of carpal bones normal or advanced; flat epiphyses or phalanges and radius; ‘snow cap’ sign of metacarpals Proximal femoral epiphyses are small and flat

Double-layered patella

Unspecific changes at the hands

Proximal femoral epiphyses are small but not as rounded as in COMP-MED Small epiphyses with ‘harlequin hat’ appearance; metaphyseal striations

Multiple epiphyseal dysplasia 21

Proximal femur

Club feet at birth, genu valga rather than genu vara; joint contractures, mild to moderate brachydactyly

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FREQUENCY OF MED There are no precise estimates regarding the collective incidence of MED. Based on the number of cases seen in growth clinics, rheumatology or genetics clinics, and compared with conditions whose incidences are known more precisely such as achondroplasia and osteogenesis imperfecta, it seems reasonable to give a prevalence of approximately one in 20 000 for MED. This figure is almost certainly an underestimation, as making the diagnosis of MED in an index case often reveals a significant number of affected relatives who had not been diagnosed previously. More is known about the relative incidence of the various types of MED. It is certain that MED caused by the COMP (cartilage oligomeric matrix protein) gene (EDM1; COMP-MED) is the most common form, accounting for at least half of cases. The second most common form, at least in Europe, is the recessive form of MED caused by mutations in the DTDST (SLC26A2) (diastrophic dysplasia sulphate transporter) gene (EDM4; rMED for recessive MED). This form accounts for approximately one-quarter of MED cases. The remaining 25% of MED cases are split between the genes MATN3, COL9A1, COL9A2 and COL9A3. Matrilin-3 mutations seem to be significantly more common than mutations in any of the three collagen 9 genes, but the number of cases is still relatively small and it is possible that collagen 9 cases may be under reported because of the lower availability of mutation analysis for those genes. Some researchers have been unable to obtain molecular confirmation in a majority of MED cases, and have thus suggested that one or more ‘major’ genes for MED may exist.4 Other groups have been far more successful, suggesting that a stringent clinical and radiographic evaluation is needed in making a diagnosis of MED, in case other adult-onset and spurious phenotypes are included.5,6 However, it is clear that some MED cases, even familial ones, are caused by genes other than those known to date. Gene mapping and mutation analysis will certainly reveal other MED genes, although they are not likely to be very common. COMP-MED (EDM1) (MIM 132400) This is the most common form of MED. It is dominantly inherited and while several denovo mutations have been reported, a family history can be elicited in more than half of cases. As in other MED forms, the newborn is clinically healthy and measurements are normal. Motor development in the first months is normal but onset of walking can be delayed or progress can be slower than average. This may be caused by laxity of large joints (knees and hips), muscular hypotonia, and (rarely) mild myopathy with mildly elevated creatine kinase and/or evidence of myopathy on muscle biopsy. Joint pain is common. It is not rare for children to present to neuropaediatric clinics for hypotonia or delayed or ‘uncoordinated’ walking. Growth retardation may be observed after 2 years of age, and a slight disproportion with mild shortening of the arms and legs with a normal trunk can occur. During the clinical course, muscular hypotonia becomes less prominent in late childhood but joint laxity persists, leading to premature osteoarthritis of the hips and knees. Joint replacement at the hip joints may be required in the third decade or later. Radiographic changes of COMP-MED In COMP-MED, there is a delay in appearance of the carpal bones. During ossification, their contour is not smooth but irregular, sometimes jagged. The phalanges may be

Multiple epiphyseal dysplasia 23

Figure 1. Hand changes in cartilage oligomeric matrix protein multiple epiphyseal dysplasia. The three panels show x rays taken at 3, 7 and 12 years of age. At 3 years, the hand shows overall delay in maturation of the carpal bones and the distal radial epiphysis; the metacarpals have small and rounded epiphyses. At 7 years, the metacarpal and phalangeal epiphyses are more normal, while the carpal bones are edgy and still markedly delayed. At 12 years, the findings are not diagnostic.

slightly shorter than normal and their epiphyses may be rounded or cone shaped. The delay in maturation affects the carpal bones more than the phalangeal epiphyses (Figure 1). The spine is not affected. The proximal femurs show a significant delay in maturation and the capital femoral epiphysis remains small and round for a much longer time than usual; this is perhaps the most useful feature in the differential diagnosis with rMED (Figure 2). At the knee joint, the distal femoral and proximal tibial epiphyses are both too small for the chronological age throughout childhood (Figure 3). The peripheral part of the metaphyses is also undermineralized, resulting in an ‘ice-cream cone’ appearance. A peculiar pattern of ossification may be observed between the approximate ages of 8–9 years and the end of puberty; ossification of the (delayed) metaphyses does not proceed homogeneously from the centre to the periphery, but a secondary, additional ossification centre (almost an ossification ‘ring’) appears. In anteroposterior radiographs, this may give the impression of a crack within the epiphysis; the ‘glacier crevice’ sign that is very helpful in the diagnosis of COMP-MED in older children (Figure 3). After puberty, when ossification is complete, no trace remains of this unusual pattern. In the adult, there is often severe osteoarthritis of the hip joint with shortening and varus defomity of the femoral neck.

Molecular basis of COMP-MED This form of MED is caused by heterozygosity for structural mutations (mostly amino acid substitutions) in the COMP gene.7,8 It must be noted that while certain mutations (e.g. R718W) have been observed repeatedly and seem to be recurrent, there is extensive mutational heterogeneity in the COMP gene.5,9,10 Thus, some mutations may result in a classical pseudoachondroplasia (PSACH) phenotype, some in a typical MED phenotype, and still others may result in ‘overlap’ phenotypes that may be called severe MED or mild PSACH.8,11 Cases who show clear vertebral anomalies in childhood have been labelled as PSACH to date, but the border is fluent and the distinction is arbitrary.

Figure 2. Radiographic appearance of the pelvis and proximal femurs in cartilage oligomeric matrix protein multiple epiphyseal dysplasia. The first panel shows the pelvis of a 3-year-old boy, the second panel shows a boy aged 7 years, and the last panel shows an adult female. In the first image, the proximal femoral epiphyses are too small for age and rounded. In the second image, the epiphyses remain too small and there is irregularity of the acetabular margin. In the last image, considerable flattening of the epiphyses has occurred secondary to cartilage degeneration, and the changes are no longer characteristic.

Multiple epiphyseal dysplasia 25

Figure 3. The three panels show knee x rays of siblings taken at 7 and 11 years of age as well as of their mother (cartilage oligomeric matrix protein R718W mutation). At 7 years, the epiphyses at the knee are small and their lateral border, in particular, is thin. At 11 years, there is an accessory ‘ring’ of cartilage ossification that gives the impression of fragmentation (the ‘glacier crevice’ sign). In the adult, the changes are no longer discernible; the only remaining feature is the small size of the epiphyses.

Recessive MED (rMED; EDM4; DTDST-MED) (MIM 226900) Clinical features In approximately one-third of individuals with rMED, there is a history of congenital club feet; otherwise, nothing suggests the diagnosis at birth. Growth is often normal, and although most individuals with rMED are slightly shorter than normal, there is much variability with some individuals having heights above the mean, even as adults.12 Unlike in COMP-MED, there is no joint laxity but rather joint limitation, and the presenting sign can be restriction of movement at the hip joint, knee joint or even interphalangeal joints. A more common presenting symptom is joint pain. The most common clinical pattern is that of a child of normal height complaining of chronic joint pain and with some degree of diffuse joint limitation. Malposition or dislocation of the proximal radius may be present, resulting in inability to extend the elbow fully. A mild degree of genu valgum is common. In older children and adults, there is concomitant ulnar incurvation of the index finger and radial incurvation of the fifth finger in a ‘bracket’ pattern. The great toe may be more prominent than the other toes, and a large sandal gap may be present. Palatal cleft or cystic ear transformation, common in diastrophic dysplasia, are not observed.1 Radiographic changes in rMED Whereas COMP-MED is characterized by small, roundish epiphyses, rMED is characterized by flat epiphyses (Figure 4). Carpal ossification delay is not a feature of rMED; instead, carpal age may be slightly advanced. Conversely, phalangeal epiphyses are both delayed in appearance and too thin or flat, and sometimes thinned on one side only. The distal epiphyses of radius and ulna are also flattened. The distal

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Figure 4. Radiographic features of the hand in recessive multiple epiphyseal dysplasia caused by DTDST mutations at 1, 6 and 12 years of age. In this condition, carpal ossification is not delayed but sometimes slightly advanced, while the metacarpal and phalangeal epiphyses are flat and delayed. Flattening of the distal metacarpal epiphyses gives a ‘snow cap’ appearance. Overall, the phalanges and metacarpal are somewhat short and plump.

metacarpal epiphyses are not round as normal but slightly flat and broadened, and tend to embrace the metacarpal bone itself, like ‘snow melting from a roof’. The radiographic appearance of the hand in rMED is very different from that in COMPMED, and while hands are usually clinically unaffected, hand x rays should be part of the diagnostic work-up of possible MED cases. The spine is not affected in childhood, but a moderate degree of scoliosis and some degree of irregularities of the vertebral bodies can be seen in older children and adults. As in the genetically related disorder diastrophic dysplasia, there may be a reduction of the vertebral interpedicular distance from L1 to L5. At the pelvis, the most distinctive sign is progressive flattening of the proximal femoral epiphysis (Figure 5). The epiphysis may be normal or just mildly flattened until 4 or 5 years of age, but then progressively decreases in height, and the femoral neck becomes broader than normal, giving the epiphysis a ‘moon sickle’ appearance. Unlike in COMP-MED, the femoral neck does not deform to a varus position, but rather to a valgus position. A particular ossification variant of the patella seems to be a distinctive and diagnostically helpful finding.1,12 The so-called double-layer patella (Figure 5) is most often seen in rMED but has been reported in one case of COL9-MED.13 The two layers are actually formed from two different ossification centres, residing in two different tendons, which fail to fuse. Molecular basis of rMED Unlike the other forms of MED, this form is inherited as a recessive trait. The phenotype of rMED was delineated originally in a series of 18 individuals homozygous for the R279W mutation in DTDST.1 This remains the genotype most often found, although other ‘mild’ mutations, such a C653S, result in the same phenotype when homozygous, and compound heterozygosity for R279W or C653S and other mutations

Multiple epiphyseal dysplasia 27

Figure 5. The pelvis in recessive multiple epiphyseal dysplasia at 7 years of age and in an adult individual. At 7 years, the femoral heads are flat and thin. In the adult, even more flattening has occurred. The right panel shows the characteristic double-layered patella in a 9-year-old girl. The two separate layers, located in two different tendons, fail to fuse.

have been observed in families with rMED.14 Affected siblings are frequently observed, suggesting that familiarity is a factor in suggesting the diagnosis, and thus, sporadic cases may go undiagnosed. The same considerations made above for COMP-MED also apply to rMED; next to the common mutation R279W, there are numerous other rare mutations that may result in either a ‘pure’ rMED phenotype or in phenotypes that overlap partially with diastrophic dysplasia (previously called ‘diastrophic variant’). MATN3-MED (EDM5) (MIM 607078) Clinical features In contrast with the other forms, the severe variant of MATN3 disease was only discovered several years after heterozygous mutations were associated with MED.15

28 S. Unger et al

MATN3 as a cause of MED was found by using linkage in a large four-generation family followed by a candidate gene approach.16 Since then, several cases have been identified but it remains a relatively rare form of MED. A single family has been reported in which a matrilin mutation was inherited as a recessive trait; the phenotype was that of spondylo-epiphyseal dysplasia in homozygous children, and heterozygotes were reported as phenotypically normal.15 Most patients present in early childhood with knee pain or knee and hip pain.17 Occasionally, genu valgum or varum is the presenting feature. Stature is often slightly reduced compared with unaffected family members, but within the lower portion of the normal growth curve.10 The hip changes are progressive and many people require hip replacements by middle age. This form of MED is associated with a high degree of intrafamilial variability.17,18 Radiographic changes of MATN3-MED In many respects, the radiographic features of MATN3-MED resemble those of COMP-MED. The epiphyses of the knees and hips are small, delayed in appearance, flattened and sometimes fragmented (Figure 6); they are not as rounded as in COMP-MED.10 The proximal femoral epiphyses are almost always radiographically affected, and are usually smaller than normal (Figure 6). The distal femoral epiphyses thin out at the sides, and when they cone in the femoral metaphysis, they may resemble a ‘harlequin hat’. Longitudinal metaphyseal striations are not uncommon in MATN3MED. Unlike in COMP-MED, the carpal bones of patients with a MATN3 presentation are delayed in appearance but smooth in contour (Figure 6). Again, one must be cautious before generalizing as many patients have not had complete radiographic examinations but only hip and knee x rays. If there are no prepubertal hand x rays, it is impossible to assess maturational delay. Despite the relatively normal stature, several patients have been noted to have minor spinal radiographic abnormalities, usually described as endplate irregularity.10

Figure 6. Features of matrilin-3-associated multiple epiphyseal dysplasia (MATN3-MED) in an 8-year-old girl. The proximal femoral epiphyses are small and already somewhat flattened. The acetabular margin is better preserved than in cartilage oligomeric matrix protein (COMP)-MED. The epiphyses at the knee are small and resemble those of COMP-MED in having thin edges; the shape of the distal femoral epiphyses in MATN3MED with the central depression is reminiscent of a ‘harlequin hat’. Metaphyseal striations may be more common in MATN3-MED than in other forms of MED. The hand shows a general delay of maturation affecting the carpal bones more than the phalangeal epiphyses. There is some phalangeal shortening in this case but this is not a universal finding in MATN3-MED.

Multiple epiphyseal dysplasia 29

Molecular basis of MATN3-MED Matrilin-3 is an important component of the cartilage extracellular membrane.19 Like the other matrilin family members, MATN3 contains a von Willebrand factor A domain, and most of the mutations (but not all) are clustered there.10,16 Most mutations are missense but at least one single base pair deletion causing a premature stop codon has been reported.8

COL9-MED (EDM2, EDM3, EDM6; MIM 600204 AND 600969) Clinical features COMP was the first gene associated with MED.7 However, it was recognized that COMP mutations accounted for only a percentage of MED cases. By using linkage analysis, a second MED (EDM2) locus was identified on chromosome 1 in the region of COL9A2.20 Indeed, a splice site mutation was subsequently identified in this gene.24 Later, analogous mutations were identified in the two other genes that encode the remaining components of type IX collagen (COL9A1 and COL9A3).21,22 However, COL9-MED appears to be quite rare in North America and Europe with only a few families reported. COL9-MED is a relatively benign form of the disorder, presenting late in the first decade of life with knee pain and stiffness. As with COMP-MED, a clinical picture mimicking a myopathy can be the presenting feature.23 Radiographic changes of COL9-MED Due to the rarity of the condition and the symptoms being mainly limited to the knees, there is a paucity of radiographs available for molecularly proven COL9MED cases; therefore, one must be cautious about making generalizations. The knees are the anatomical site most consistently radiographed, and often have significant abnormalities such as flattened and irregular epiphyses.24,25 There is a general trend towards more severe involvement of the knees than the hips compared with COMP-MED.25,26 COL9-MED seems to be more common in Japanese populations, and several families have been documented. These families demonstrate that despite a lack of symptoms, many epiphyses are radiographically abnormal, especially at the wrists and ankles.5,25 Few patients have had spinal x rays but those are reported as normal.23,27 Molecular basis of COL9-MED Type IX collagen is a structural component of the extracellular matrix and is a heterotrimer composed from one chain each of COL9A1, COL9A2 and COL9A3. It is a fibril-associated collagen with interrupted triple helices. Each peptide chain has three collagenous domains separated by four non-collagenous domains.28 Interestingly, all mutations found to date have been of the exon skipping variety predicted to cause a loss of amino acids in the third collagenous domain.21,22,24,29 Despite complete sequencing of the gene in several MED patients, no other mutations have been found.5

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Practice points  MED is genetically heterogeneous  suspicion of MED should be raised in any child with bilateral Perthes disease  MED should also be considered in any child with non-inflammatory joint pain, especially involving the knees  family history of early joint replacement is a possible indicator of MED  children with MED are often slightly short but can have a height above the third percentile  full skeletal survey, including lateral knee, is important for the diagnosis  following a diagnosis of MED, counselling should be given to avoid high-impact sports

Research agenda  genetic mapping of families with MED not caused by one of the six known genes  further analysis of the known genes to determine what role they play in sporadic osteoarthritis  explore the therapeutic potential of siRNA in the dominant negative forms of MED

ACKNOWLEDGEMENTS The authors wish to thank their colleagues who submitted radiographs for review and DNA samples for analysis, as well as colleagues at the European Skeletal Dysplasia Network (www.esdn.org) for sharing radiographic expertise and results of molecular studies. REFERENCES *1. Ballhausen D, Bonafe L, Terhal P et al. Recessive multiple epiphyseal dysplasia (rMED): phenotype delineation in eighteen homozygotes for DTDST mutation R279W. Journal of Medical Genetics 2003; 40: 65–71. 2. Haga N, Nakamura K, Takikawa K et al. Stature and severity in multiple epiphyseal dysplasia. Journal of Pediatric Orthopaedics 1998; 18: 394–397. *3. Jakkula E, Lohiniva J, Capone A et al. A recurrent R718W mutation in COMP results in multiple epiphyseal dysplasia with mild myopathy: clinical and pathogenetic overlap with collagen IX mutations. Journal of Medical Genetics 2003; 40: 942–948. 4. Jakkula E, Makitie O, Czarny-Ratacjzak M et al. Mutations in the known genes are not the major cause of MED; distinctive phenotypic entities among patients with no identified mutations. European Journal of Human Genetics 2005; 13: 292–301. *5. Itoh T, Shirahama S, Nakashima E et al. Comprehensive screening of multiple epiphyseal dysplasia mutations in Japanese population. American Journal of Medical Genetics A 2006; 140: 1280–1284. 6. Zankl A, Jackson GC, Crettol LM et al. Preselection of cases through expert clinical and radiological review significantly increases mutation detection rate in multiple epiphyseal dysplasia. European Journal of Human Genetics 2007; 15: 150–154.

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32 S. Unger et al 28. Pihlajamaa T, Vuoristo MM, Annunen S et al. Human COL9A1 and COL9A2 genes. Two genes of 90 and 15 kb code for similar polypeptides of the same collagen molecule. Matrix Biology 1998; 17: 237–241. 29. Lohiniva J, Paassilta P, Seppanen U et al. Splicing mutations in the COL3 domain of collagen IX cause multiple epiphyseal dysplasia. American Journal of Medical Genetics 2000; 90: 216–222.