Valérie Cormier-Daire

Nosology and classification of genetic skeletal disorders: 2010 revision

The objective of the paper is to provide the revision of the Nosology of Constitutional Disorders of Bone that incorporates newly recognized disorders and reflects new molecular and pathogenetic concepts. Criteria for inclusion of disorders were (1) significant skeletal involvement corresponding to the definition of skeletal dysplasias, metabolic bone disorders, dysostoses, and skeletal malformation and/or reduction syndromes, (2) publication and/or MIM listing, (3) genetic basis proven or very likely, and (4) nosologic autonomy confirmed by molecular or linkage analysis and/or distinctive diagnostic features and observation in multiple individuals or families. Three hundred seventy‐two different conditions were included and placed in 37 groups defined by molecular, biochemical and/or radiographic criteria. Of these conditions, 215 were associated with one or more of 140 different genes. Nosologic status was classified as final (mutations or locus identified), probable (pedigree evidence), or bona fide (multiple observations and clear diagnostic criteria, but no pedigree or locus evidence yet). The number of recognized genetic disorders with a significant skeletal component is growing and the distinction between dysplasias, metabolic bone disorders, dysostoses, and malformation syndromes is blurring. For classification purposes, pathogenetic and molecular criteria are integrating with morphological ones but disorders are still identified by clinical features and radiographic appearance. Molecular evidence leads to confirmation of individual entities and to the constitution of new groups, but also allows for delineation of related but distinct entities and indicates a previously unexpected heterogeneity of molecular mechanisms; thus, molecular evidence does not necessarily simplify the Nosology, and a further increase in the number of entities and growing complexity is expected. By providing an updated overview of recognized entities with skeletal involvement and of the underlying gene defects, the new Nosology can provide practical diagnostic help, facilitate the recognition of new entities, and foster and direct research in skeletal biology and genetic disorders.

Mutations in STAT3 and IL12RB1 impair the development of human IL-17–producing T cells

The cytokines controlling the development of human interleukin (IL) 17–producing T helper cells in vitro have been difficult to identify. We addressed the question of the development of human IL-17–producing T helper cells in vivo by quantifying the production and secretion of IL-17 by fresh T cells ex vivo, and by T cell blasts expanded in vitro from patients with particular genetic traits affecting transforming growth factor (TGF) β, IL-1, IL-6, or IL-23 responses. Activating mutations in TGFB1, TGFBR1, and TGFBR2 (Camurati-Engelmann disease and Marfan-like syndromes) and loss-of-function mutations in IRAK4 and MYD88 (Mendelian predisposition to pyogenic bacterial infections) had no detectable impact. In contrast, dominant-negative mutations in STAT3 (autosomal-dominant hyperimmunoglobulin E syndrome) and, to a lesser extent, null mutations in IL12B and IL12RB1 (Mendelian susceptibility to mycobacterial diseases) impaired the development of IL-17–producing T cells. These data suggest that IL-12Rβ1– and STAT-3–dependent signals play a key role in the differentiation and/or expansion of human IL-17–producing T cell populations in vivo.

Mutations of the SCO1 Gene in Mitochondrial Cytochrome c Oxidase Deficiency with Neonatal-Onset Hepatic Failure and Encephalopathy

Cytochrome c oxidase (COX) catalyzes both electron transfer from cytochrome c to molecular oxygen and the concomitant vectorial proton pumping across the inner mitochondrial membrane. Studying a large family with multiple cases of neonatal ketoacidotic comas and isolated COX deficiency, we have mapped the disease locus to chromosome 17p13.1, in a region encompassing two candidate genes involved in COX assembly-namely, SCO1 and COX10. Mutation screening revealed compound heterozygosity for SCO1 gene mutations in the patients. The mutated allele, inherited from the father, harbored a 2-bp frameshift deletion (DeltaGA; nt 363-364) resulting in both a premature stop codon and a highly unstable mRNA. The maternally inherited mutation (C520T) changed a highly conserved proline into a leucine in the protein (P174L). This proline, adjacent to the CxxxC copper-binding domain of SCO1, is likely to play a crucial role in the tridimentional structure of the domain. Interestingly, the clinical presentation of SCO1-deficient patients markedly differs from that of patients harboring mutations in other COX assembly and/or maturation genes.

Loss-of-function mutations in euchromatin histone methyl transferase 1 (EHMT1) cause the 9q34 subtelomeric deletion syndrome.

A clinically recognizable 9q subtelomeric deletion syndrome has recently been established. Common features seen in these patients are severe mental retardation, hypotonia, brachycephaly, flat face with hypertelorism, synophrys, anteverted nares, cupid bow or tented upper lip, everted lower lip, prognathism, macroglossia, conotruncal heart defects, and behavioral problems. The minimal critical region responsible for this 9q subtelomeric deletion (9q-) syndrome has been estimated to be <1 Mb and comprises the euchromatin histone methyl transferase 1 gene (EHMT1). Previous studies suggested that haploinsufficiency for EHMT1 is causative for 9q subtelomeric deletion syndrome. We have performed a comprehensive mutation analysis of the EHMT1 gene in 23 patients with clinical presentations reminiscent of 9q subtelomeric deletion syndrome. This analysis revealed three additional microdeletions that comprise the EHMT1 gene, including one interstitial deletion that reduces the critical region for this syndrome. Most importantly, we identified two de novo mutations--a nonsense mutation and a frameshift mutation--in the EHMT1 gene in patients with a typical 9q- phenotype. These results establish that haploinsufficiency of EHMT1 is causative for 9q subtelomeric deletion syndrome.

CHARGE syndrome: Report of 47 cases and review

The acronym CHARGE refers to a syndrome of unknown cause. Here we report on 47 CHARGE patients evaluated for the frequency of major anomalies, namely coloboma (79%), heart malformation (85%), choanal atresia (57%), growth and/or mental retardation (100%), genital anomalies (34%), ear anomalies (91%), and/or deafness (62%). In addition, we comment on anomalies observed very frequently in neonates and infants with the CHARGE syndrome, including, minor facial anomalies, neonatal brain stem dysfunction with cranial nerve palsy, and, mostly, internal ear anomalies such as semicircular canal hypoplasia that were found in each patient that could be tested. We propose several criteria for poor survival including male gender, central nervous system and/or oesophageal malformations, and bilateral choanal atresia. No predictive factor regarding developmental prognosis could be identified in our series. A significantly higher mean paternal age at conception together with concordance in monozygotic twins and the existence of rare familial cases support the role of genetic factors such as de novo mutation of a dominant gene or subtle sub-microscopic chromosome rearrangement. Finally, the combination of malformations in CHARGE syndrome strongly supports the view that this multiple congenital anomalies/mental retardation syndrome is a polytopic developmental field defect involving the neural tube and the neural crests cells.

Large-Scale Deletion and Point Mutations of the Nuclear NDUFV1 and NDUFS1 Genes in Mitochondrial Complex I Deficiency

Reduced nicotinamide adenine dinucleotide (NADH):ubiquinone oxidoreductase (complex I) is the largest complex of the mitochondrial respiratory chain and complex I deficiency accounts for approximately 30% cases of respiratory-chain deficiency in humans. Only seven mitochondrial DNA genes, but >35 nuclear genes encode complex I subunits. In an attempt to elucidate the molecular bases of complex I deficiency, we studied the six most-conserved complex I nuclear genes (NDUFV1, NDUFS8, NDUFS7, NDUFS1, NDUFA8, and NDUFB6) in a series of 36 patients with isolated complex I deficiency by denaturing high-performance liquid chromatography and by direct sequencing of the corresponding cDNA from cultured skin fibroblasts. In 3/36 patients, we identified, for the first time, five point mutations (del222, D252G, M707V, R241W, and R557X) and one large-scale deletion in the NDUFS1 gene. In addition, we found six novel NDUFV1 mutations (Y204C, C206G, E214K, IVS 8+41, A432P, and del nt 989-990) in three other patients. The six unrelated patients presented with hypotonia, ataxia, psychomotor retardation, or Leigh syndrome. These results suggest that screening for complex I nuclear gene mutations is of particular interest in patients with complex I deficiency, even when normal respiratory-chain-enzyme activities in cultured fibroblasts are observed.

ADAMTS10 Mutations in Autosomal Recessive Weill-Marchesani Syndrome

Weill-Marchesani syndrome (WMS) is characterized by the association of short stature; brachydactyly; joint stiffness; eye anomalies, including microspherophakia and ectopia of the lenses; and, occasionally, heart defects. We have recently mapped a gene for the autosomal recessive form of WMS to chromosome 19p13.3-p13.2, in a 12.4-cM interval. Here, we report null mutations in a member of the extracellular matrix protease family, the gene encoding ADAMTS10, a disintegrin and metalloprotease with thrombospondin motifs. A total of three distinct mutations were identified in two consanguineous families and in one sporadic WMS case, including one nonsense mutation (R237X) and two splice mutations (1190+1G-->A and 810+1G-->A). ADAMTS10 expression studies using reverse-transcriptase polymerase chain reaction, northern blot, and dot-blot analyses showed that ADAMTS10 is expressed in skin, fetal chondrocytes, and fetal and adult heart. Moreover, electron microscopy and immunological studies of the skin fibroblasts from the patients confirmed impairment of the extracellular matrix. We conclude, therefore, that ADAMTS10 plays a major role in growth and in skin, lens, and heart development in humans.

Molecular basis of variant pseudo-Hurler polydystrophy (mucolipidosis IIIC)

Mucolipidosis IIIC, or variant pseudo-Hurler polydystrophy, is an autosomal recessive disease of lysosomal hydrolase trafficking. Unlike the related diseases, mucolipidosis II and IIIA, the enzyme affected in mucolipidosis IIIC (N-Acetylglucosamine-1-phosphotransferase [GlcNAc-phosphotransferase]) retains full transferase activity on synthetic substrates but lacks activity on lysosomal hydrolases. Bovine GlcNAc-phosphotransferase has recently been isolated as a multisubunit enzyme with the subunit structure alpha(2)beta(2)gamma(2). We cloned the cDNA for the human gamma-subunit and localized its gene to chromosome 16p. We also showed, in a large multiplex Druze family that exhibits this disorder, that MLIIIC also maps to this chromosomal region. Sequence analysis of the gamma-subunit cDNA in patients from 3 families identified a frameshift mutation, in codon 167 of the gamma subunit, that segregated with the disease, indicating MLIIIC results from mutations in the phosphotransferase gamma-subunit gene. This is to our knowledge the first description of the molecular basis for a human mucolipidosis and suggests that the gamma subunit functions in lysosomal hydrolase recognition.

A broad spectrum of clinical presentations in congenital disorders of glycosylation I: a series of 26 cases

INTRODUCTION Congenital disorders of glycosylation (CDG), or carbohydrate deficient glycoprotein syndromes, form a new group of multisystem disorders characterised by defective glycoprotein biosynthesis, ascribed to various biochemical mechanisms. METHODS We report the clinical, biological, and molecular analysis of 26 CDG I patients, including 20 CDG Ia, two CDG Ib, one CDG Ic, and three CDG Ix, detected by western blotting and isoelectric focusing of serum transferrin. RESULTS Based on the clinical features, CDG Ia could be split into two subtypes: a neurological form with psychomotor retardation, strabismus, cerebellar hypoplasia, and retinitis pigmentosa (n=11), and a multivisceral form with neurological and extraneurological manifestations including liver, cardiac, renal, or gastrointestinal involvement (n=9). Interestingly, dysmorphic features, inverted nipples, cerebellar hypoplasia, and abnormal subcutaneous fat distribution were not consistently observed in CDG Ia. By contrast, the two CDG Ib patients had severe liver disease, enteropathy, and hyperinsulinaemic hypoglycaemia but no neurological involvement. Finally, the CDG Ic patient and one of the CDG Ix patients had psychomotor retardation and seizures. The other CDG Ix patients had severe proximal tubulopathy, bilateral cataract, and white matter abnormalities (one patient), or multiorgan failure and multiple birth defects (one patient). CONCLUSIONS Owing to the remarkable clinical variability of CDG, this novel disease probably remains largely underdiagnosed. The successful treatment of CDG Ib patients with oral mannose emphasises the paramount importance of early diagnosis of PMI deficiency.

Germline mutations in WTX cause a sclerosing skeletal dysplasia but do not predispose to tumorigenesis

Abnormalities in WNT signaling are implicated in a broad range of developmental anomalies and also in tumorigenesis. Here we demonstrate that germline mutations in WTX (FAM123B), a gene that encodes a repressor of canonical WNT signaling, cause an X-linked sclerosing bone dysplasia, osteopathia striata congenita with cranial sclerosis (OSCS; MIM300373). This condition is typically characterized by increased bone density and craniofacial malformations in females and lethality in males. The mouse homolog of WTX is expressed in the fetal skeleton, and alternative splicing implicates plasma membrane localization of WTX as a factor associated with survival in males with OSCS. WTX has also been shown to be somatically inactivated in 11–29% of cases of Wilms tumor. Despite being germline for such mutations, individuals with OSCS are not predisposed to tumor development. The observed phenotypic discordance dependent upon whether a mutation is germline or occurs somatically suggests the existence of temporal or spatial constraints on the action of WTX during tumorigenesis.