Metaphyseal anadysplasia: evidence of genetic heterogeneity

Prenatal course of metaphyseal anadysplasia associated with homozygous mutation in MMP9 identified by exome sequencing

Metaphyseal anadysplasia (MANDP) is a rare autosomal recessive form of skeletal dysplasia characterized by normal length at birth and transitory bowing of the legs. Although several families with MANDP have been reported, homozygous mutations in the matrix metalloproteinase type 9 (MMP9) gene have been described in only one consanguineous family, and thus the pre and postnatal phenotypic spectrum is still obscure. A clinically similar but more severe type is caused by autosomal-dominant inheritance and is caused by mutations in matrix metalloproteinase type 13 gene (MMP13). Here, we report the prenatal and early postnatal course of two affected sib fetuses with early sonographic evidence of long bone shortening and postnatally no metaphyseal changes. Whole-exome sequencing revealed homozygous mutation in MMP9 in both fetuses suggesting a diagnosis of MANDP. We propose that MANDP should be considered in pregnancies with early prenatal shortening of the long bones without associated finding of lethal skeletal dysplasias. In addition, the finding of homozygous mutation in non-consanguineous parents of Jewish-Caucasus ancestry may suggest unawareness of such relation or the occurrence of a founder mutation in this gene.

Metaphyseal dysplasia, Spahr type; missense MMP13 mutations in two Iraqi siblings

We report on two siblings of Iraqi descent with clinical and radiographic features of metaphyseal dysplasia, Spahr type (MDST), born to consanguineous unaffected parents. Molecular testing confirmed pathogenic mutations in MMP13. We review the considerable overlap between MDST and other related disorders. These cases confirm the phenotypic variability and regressive nature of MDST in addition to suggesting bone fragility as a feature.

Exome sequencing reveals a nonsense mutation in MMP13 as a new cause of autosomal recessive metaphyseal anadysplasia

Metaphyseal anadysplasia (MANDP) is an uncommon chondrodysplasia characterized by early-onset metaphyseal dysplasia and short stature that improves with age. MANDP is caused by mutations in the matrix metalloproteinase (MMP) 9 and 13 genes. Autosomal dominant (AD) MANDP has been described as more severe, and has been associated with dominant-negative MMP13 mutations that suppress activity of both MMP9 and MMP13; autosomal recessive (AR) MANDP has been described as a milder form associated with AR missense mutations in MMP9 or MMP13. Here we describe the molecular characterization of skeletal dysplasia in two brothers who presented with short stature and mixed epiphyseal and metaphyseal dysplasia. Whole-exome sequencing (WES) identified a homozygous C>T transition mutation in exon 2 of MMP13 (c.325C>T) on chromosome 11q22.2 resulting in a premature stop codon p.(R109*) that is predicted to abolish MMP13 activity. This report extends the MANDP phenotype by illustrating that AR nonsense mutations in MMP13 can lead to short stature that persists beyond childhood.

Mutations in MMP9 and MMP13 determine the mode of inheritance and the clinical spectrum of metaphyseal anadysplasia

The matrix metalloproteinases MMP9 and MMP13 catalyze the degradation of extracellular matrix (ECM) components in the growth plate and at the same time cleave and release biologically active molecules stored in the ECM, such as VEGFA. In mice, ablation of Mmp9, Mmp13, or both Mmp9 and Mmp13 causes severe distortion of the metaphyseal growth plate. We report that mutations in either MMP9 or MMP13 are responsible for the human disease metaphyseal anadysplasia (MAD), a heterogeneous group of disorders for which a milder recessive variant and a more severe dominant variant are known. We found that recessive MAD is caused by homozygous loss of function of either MMP9 or MMP13, whereas dominant MAD is associated with missense mutations in the prodomain of MMP13 that determine autoactivation of MMP13 and intracellular degradation of both MMP13 and MMP9, resulting in a double enzymatic deficiency.

Reversible metaphyseal dysplasia, a novel bone phenotype, in two unrelated children with autoimmunepolyendocrinopathy-candidiasis-ectodermal dystrophy: clinical and molecular studies

We report the association of an undescribed, reversible metaphyseal dysplasia (RMD) with autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) in two patients, one homozygous and one heterozygous for a 13-bp deletion in exon 8 of the autoimmune regulator (AIRE) gene. One patient also had a novel deletion in exon 6, resulting in a frameshift mutation and introduction of a STOP codon in exon 10. Their APECED phenotypes differed, but both patients developed progressive skeletal deformities and growth failure from early childhood. Radiological examination suggested a generalized abnormality of endochondral ossification, with irregular, flared, radioopaque regions in the metaphyses, subjacent to the growth plates. Histopathology in patient 1 showed islands of calcified cartilage within bone, consistent with impaired coupling of cartilage resorption with vascular invasion and ossification. Despite discordance for puberty, both patients experienced radiological resolution of their bone disease in their mid-teens, with improvement in histopathology in patient 1. RMD may constitute a rare phenotypic variation of APECED, possibly resulting from autoimmunity directed against skeletal proteins. We also demonstrated AIRE expression in chondrocytes derived from human fetal growth plates, primary culture of human chondrocytes, and two chondrosarcoma cell lines, suggesting a potential role for abnormal AIRE expression in the development of RMD.

Distinctive metaphyseal chondrodysplasia with severe distal radius and ulna involvement (upper extremity mesomelia) and normal height

Metaphyseal chondrodysplasias (MCD) are skeletal disorders characterized by metaphyseal irregularities and, usually, by short stature. In MCD, wide heterogeneity exists with regard to clinical and radiological changes. We report on a patient with clinical and radiological findings of MCD who had coxa valga and normal height with metaphyseal involvement of the long bones. The short radii and ulnae showed a very severe change in their distal metaphyses, leading to mesomelic shortening confined to the upper limbs. Hematological, ophthalmological, and hearing examinations were normal. This type of MCD appears to represent a yet undescribed syndrome.