366 LETTER TO JMG Spondylo-epi-metaphyseal dysplasia (SEMD) matrilin 3 type: homozygote matrilin 3 mutation in a novel form of J Med Genet: first published as on 30 April 2004. Downloaded from SEMD Z U Borochowitz*, D Scheffer*, V Adir, N Dagoneau, A Munnich, V Cormier-Daire ............................................................................................................................... J Med Genet 2004;41:366–372. doi: 10.1136/jmg.2003.013342 steochondrodysplasia is a heterogeneous group of Key points conditions caused by impaired development of oss- Oeous skeleton. Within this group, spondylo-epi- metaphyseal dysplasia (SEMD) represents a subgroup which N We investigated a large consanguineous Arabic- includes a number of conditions associated with vertebral, Muslim family in which five affected individuals were epiphyseal, and metaphyseal anomalies. The International diagnosed with a novel form of autosomal recessive Classification recognises at least 15 distinct entities within spondylo-epi-metaphyseal dysplasia (SEMD). All five this group as defined by a combination of clinical, radi- affected individuals presented with disproportionate ological, and molecular data.1 Mutations in the genes early-onset dwarfism, bowing of the lower limbs, encoding structural proteins of the cartilage extracellular lumbar lordosis, and normal hands. Skeletal findings matrix (that is, cartilage oligomeric matrix protein, type II included short, wide, and stocky long bones with collagen, perlecan) or involved in posttranslational process- severe epiphyseal and metaphyseal changes, hypo- ing and transport (lysosomal storage disorders, sulfation plastic iliac bones, and flat-ovoid vertebral bodies. protein (PAPSS2), regulator of chromatin (SMARCAL1), N Genome wide homozygosity mapping mapped the transcription initiation factor kinase (EIFKA3)) have been disease locus gene to chromosome 2p25–24 with a previously shown to be responsible for different forms of SEMD.1–6 However, a large number of SEMD conditions are maximum LOD score of 3.46 at locus D2S305. Two still defined on purely descriptive features. Here, we describe recombination events defined the minimal critical http://jmg.bmj.com/ five patients from a large consanguineous family of Arabic- region interval between loci D2S320 and D2S215 Muslim origin with short-limb dwarfism with distinct (2.24 Mb). Using a candidate gene approach, we skeletal dysplasia which, to our knowledge, has not been identified, in all affected individuals, a homozygous described previously. The manifestations and a constellation substitution (973T.A)inthegeneencodingfor of radiographic bony abnormalities are unique in this entity. Matrilin 3 (MATN3), a cartilage specific protein. The As there are abnormalities in the vertebral bodies, long bones, mutations changed a cysteine into a serine in the EGF- and specifically the lower limbs involving epiphyses and domain of MATN3, in a region highly conserved on September 29, 2021 by guest. Protected copyright. metaphyses, we suggest that this entity be called spondylo- across species. epi-metaphyseal dysplasia, bowed-legs type. This hitherto N We conclude that homozygous MATN3 mutations are unreported form of autosomal recessive SEMD is caused by responsible for this novel form of SEMD. homozygous mutation in matrilin 3 (MATN3), a component of the extracellular matrix of cartilage. This finding not only provides a molecular explanation for a novel form of SEMD but also expands the phenotype range of MATN3 defects legs, waddling gait, wide joints (especially the knees), with which have been previously identified in autosomal limited elbow extension, pectus excavatum, and lumbar dominant epiphyseal dysplasia and idiopathic hand osteo- lordosis. At age 10 years, she underwent bilateral osteotomy 78 arthritis. of both proximal tibiae due to severe bowing. Examination at age 12 years showed the same changes (height at -4 SD), METHODS severe waddling gait, and very pronounced bowing of lower In this family, five affected individuals were found to have limbs. disproportionate dwarfism with similar clinical and radi- Patient 2, the brother of the propositus (figs 1 and 2), had ological features. Patient 1 (figs 1 and 2) was born to healthy short limbs at birth (length 45 cm (-2 SD), head circumfer- parents of Arabic-Muslim origin who are first cousins and of ence 34 cm). At 4 months, he had bowed lower legs, and normal stature (father 175 cm (75th centile) and mother mild lumbar lordosis (length 55 cm, -3 SD). On follow-up, he 168 cm (50th centile)), after a term pregnancy and normal was noted to have short limbs, severe short stature, small delivery (birth weight 3100 g, birth length 45 cm (-2 SD), chest, lumbar lordosis, and waddling gait. No hyperlaxity of head circumference 33 cm). At 1 year, she had short-limbed joints was noted. short stature (height 68 cm (-3 SD), weight 8 kg (3rd Patient 3 is the second brother of the propositus (fig 1). At centile), head circumference 43 cm (-3 SD), arm span 33 weeks of gestation, ultrasound had detected short limbs. 71 cm, palm length 5.2 cm (50th centile), middle finger length 3.2 cm (3rd centile)). Neurological examination, psychomotor development, hearing, and visual acuity were Abbreviations: ACFD, acrocapital femoral dysplasia; BDA1, brachydactyly type A1; LAPTM4A, lysosomal-associated protein otherwise normal. Routine chemistry, thyroid function tests, transmembrane 4; MATN3, matrilin 3; MED, multiple epiphyseal and renal ultrasounds were normal as well. Re-evaluation at dysplasia; OA, osteoarthritis; SEMD, spondylo-epi-metaphyseal 6 years showed further disproportion of limbs, with bowed dysplasia www.jmedgenet.com Letter to JMG 367 J Med Genet: first published as on 30 April 2004. Downloaded from Figure 1 Pedigree of the family and genotype analysis of eight markers within the linked region on chromosome 2. http://jmg.bmj.com/ on September 29, 2021 by guest. Protected copyright. Figure 2 Patients 1 and 2: total AP and lateral view of the body. Note the short trunk and severe bowing of legs. www.jmedgenet.com 368 Letter to JMG He was delivered normally at 39 weeks and examination at hands were normal. The iliac wings were dysplastic and birth showed short limbs (length 44 cm (-2 SD), head square with narrowing of the greater sciatic notch. The circumference 33 cm). Recent examination at 4 months acetabular roof was flat, projecting medially from the roof showed short limbs and bowed thighs. No chest narrowing with a bony spike, giving rise to a trident configuration of the or joint hyperlaxity was noted. iliac bone. The pubic bones were hypoplastic with small and Patient 4, the brother of the father of the propositus (fig 1), underossified ischia. Epiphyseal and metaphyseal changes as was born to parents who were first cousins. He was first well as spinal changes increased in severity with time J Med Genet: first published as on 30 April 2004. Downloaded from examined at 23 years of age (head circumference 52.5 cm (fig 3B,D). (-2.5 SD), height 136 cm (-5 SD), arm span 147 cm, palm It should be emphasised that in the family reported here, length 11 cm (90th centile), middle finger length 7.6 cm none of the obligate heterozygote parents or the carrier (50th centile)). He had a waddling gait since he started healthy sib sister of the propositus (fig 1) ever complained of walking (at 1 year), short limbs with severe short stature, knee or hip pain or hand osteoarthritis or underwent surgery bowing of lower limbs, and severe lumbar lordosis. At 13 for early-onset osteoarthritis. A complete skeletal radio- years of age, he underwent bilateral osteotomy of both graphic evaluation of the propositus’ parents as adults, and proximal tibiae for severe bowing. On follow-up at age 32, he of the healthy sib sister as a teenager, did not reveal any is married with four children, all with regular height. skeletal changes or any epiphyseal dysplasia. Patient 5 is the half-cousin of the propositus (fig 1). He Approval was obtained from the National Helsinki was born to parents who were first cousins after a 41 week Committee for Genetic Research in Humans, and informed pregnancy (birth weight 3000 g). Waddling gait was noted consent was given by family members or parents of the when he began walking at approximately 1 year of age. At affected minors. Homozygosity mapping of the disease gene age 11.5 years, he had short-limbed short stature (height of was performed using a panel of 400 markers at an average 117 cm (-4 SD), head circumference 51 cm (10th centile), distance of 10 cM. Genomic DNA was extracted from arm span 122 cm, palm length 5.2 cm (50th centile), middle leukocytes according to standard procedures. The MLINK finger length 3.2 cm (3rd centile)). He had a flat face, normal program of the linkage software package was used to shaped chest, short limbs, hyperlordosis of the lumbar area, calculate two-point LOD scores between the disease pheno- wide joints, with limited extension of elbows, and bowed type and each of the markers, assuming a recessive disease lower limbs. On follow-up at age 23 years (height 130 cm), with an allele frequency of 0.001. the same clinical features were noted. He conducted a normal A series of 18 primers was used to amplify the eight coding life and drove a car. exons of the MATN3 gene (including intron–exon bound- x Ray radiographs of patient 3 at birth were similar to those aries) as previously described.7 at 3 months (fig 3A) and showed ribs of normal length, with Amplified products were purified and sequenced using the posteriorly marked cupping. In the lateral projection, most of fluorescent dideoxyterminator method on an ABI 3100 the vertebral bodies had an oval shape. In the AP projection, automatic sequencer. http://jmg.bmj.com/ vertebral bodies were flat. The long tubular limb bones (except those of the hands and feet) were abnormally short with a stocky appearance and relatively wide metaphyses RESULTS with lateral spurs.