Osteodysplastic primordial dwarfism: report of a further case with manifestations similar to those of types I and III

Lowry-Wood syndrome: further evidence of association with RNU4ATAC, and correlation between genotype and phenotype

Lowry-Wood syndrome (LWS) is a skeletal dysplasia characterized by multiple epiphyseal dysplasia associated with microcephaly, developmental delay and intellectual disability, and eye involvement. Pathogenic variants in RNU4ATAC, an RNA of the minor spliceosome important for the excision of U12-dependent introns, have been recently associated with LWS. This gene had previously also been associated with microcephalic osteodysplastic primordial dwarfism (MOPD) and Roifman syndrome (RS), two distinct conditions which share with LWS some skeletal and neurological anomalies. We performed exome sequencing in two individuals with Lowry-Wood syndrome. We report RNU4ATAC pathogenic variants in two further patients. Moreover, an analysis of all RNU4ATAC variants reported so far showed that FitCons scores for nucleotides mutated in the more severe MOPD are higher than RS or LWS and that they were more frequently located in the 5' Stem-Loop of the RNA critical for the formation of the U4/U6.U5 tri-snRNP complex, whereas the variants are more dispersed in the other conditions. We are thus confirming that RNU4ATAC is the gene responsible for LWS and provide a genotype-phenotype correlation analysis.

The expanding phenotype of RNU4ATAC pathogenic variants to Lowry Wood syndrome

RNU4ATAC pathogenic variants to date have been associated with microcephalic osteodysplastic primordial dwarfism, type 1 and Roifman syndrome. Both conditions are clinically distinct skeletal dysplasias with microcephalic osteodysplastic primordial dwarfism, type 1 having a more severe phenotype than Roifman syndrome. Some of the overlapping features of the two conditions include developmental delay, microcephaly, and immune deficiency. The features also overlap with Lowry Wood syndrome, another rare but well-defined skeletal dysplasia for which the genetic etiology has not been identified. Characteristic features include multiple epiphyseal dysplasia and microcephaly. Here, we describe three patients with Lowry Wood syndrome with biallelic RNU4ATAC pathogenic variants. This report expands the phenotypic spectrum for biallelic RNU4ATAC disorder causing variants and is the first to establish the genetic cause for Lowry Wood syndrome.

Microcephalic Osteodysplastic Primordial Dwarfism, Type II: a Clinical Review

PURPOSE OF THE REVIEW

This review will provide an overview of the microcephalic primordial dwarfism (MPD) class of disorders and provide the reader comprehensive clinical review with suggested care guidelines for patients with microcephalic osteodysplastic primordial dwarfism, type II (MOPDII).

RECENT FINDINGS

Over the last 15 years, significant strides have been made in the diagnosis, natural history, and management of MOPDII. MOPDII is the most common and well described form of MPD. The classic features of the MPD group are severe pre- and postnatal growth retardation, with marked microcephaly. In addition to these features, individuals with MOPDII have characteristic facies, skeletal dysplasia, abnormal dentition, and an increased risk for cerebrovascular disease and insulin resistance. Biallelic loss-of-function mutations in the pericentrin gene cause MOPDII, which is inherited in an autosomal recessive manner.

Refining the phenotypical and mutational spectrum of Taybi-Linder syndrome

Taybi-Linder syndrome (TALS, OMIM 210710) is a rare autosomal recessive disorder belonging to the group of microcephalic osteodysplastic primordial dwarfisms (MOPD). This syndrome is characterized by short stature, skeletal anomalies, severe microcephaly with brain malformations and facial dysmorphism, and is caused by mutations in RNU4ATAC. RNU4ATAC is transcribed into a non-coding small nuclear RNA which is a critical component of the minor spliceosome. We report here four foetuses and four unrelated patients with RNU4ATAC mutations. We provide antenatal descriptions of this rare syndrome including unusual features found in two twin foetuses with compound heterozygosity for two rare mutations who presented with mild intrauterine growth retardation and atypical dysmorphic facial features. We also carried out a literature review of the patients described up to now with RNU4ATAC mutations, affected either with TALS or Roifman syndrome, a recently described allelic disorder.

The neurologic findings in Taybi-Linder syndrome (MOPD I/III): case report and review of the literature

Taybi-Linder syndrome, also known as microcephalic osteodysplastic primordial dwarfism types I and III, is a rare disorder with presumed autosomal recessive inheritance. It is characterized by intrauterine growth retardation, distinctive bone dysplasia, and central nervous system malformations. We present two siblings with Taybi-Linder syndrome, with an emphasis on the neurological profile in this disease, which includes brain malformations, intractable epilepsy, sensory deficits, profound cognitive deficits, and neuroendocrine dysfunction. We also present distinctive correlative neuroimaging (MRI) and electroencephalographic (EEG) findings. Increased knowledge of the neurological profile of Taybi-Linder syndrome may be helpful for clinicians and genetic counselors managing these patients.

A homozygous mutation in RNU4ATAC as a cause of microcephalic osteodysplastic primordial dwarfism type I (MOPD I) with associated pigmentary disorder

The designation microcephalic osteodysplastic primordial dwarfism (MOPD) refers to a group of autosomal recessive disorders, comprising microcephaly, growth retardation, and a skeletal dysplasia. The different types of MOPD have been delineated on the basis of clinical, radiological, and genetic criteria. We describe two brothers, born to healthy, consanguineous parents, with intrauterine and postnatal growth retardation, microcephaly with abnormal gyral pattern and partial agenesis of corpus callosum, and skeletal anomalies reminiscent of those described in MOPD type I. This was confirmed by the identification of the homozygous g.55G > A mutation of RNU4ATAC encoding U4atac snRNA. The sibs had yellowish-gray hair, fair skin, and deficient retinal pigmentation. Skin biopsy showed abnormal melanin function but OCA genes were normal. The older sib had an intracranial hemorrhage at 1 week after birth, the younger developed chilblains-like lesions at the age 2½ years old but analysis of the SAMHD1 and TREX1 genes did not show any mutations. To the best of our knowledge, vasculopathy and pigmentary disorders have not been reported in MOPD I.

Microcephalic osteodysplastic primordial dwarfism type I with biallelic mutations in the RNU4ATAC gene

Microcephalic osteodysplastic primordial dwarfism type I (MOPD I) is a rare autosomal recessive developmental disorder characterized by extreme intrauterine growth retardation, severe microcephaly, central nervous system abnormalities, dysmorphic facial features, skin abnormalities, skeletal changes, limb deformations, and early death. Recently, mutations in the RNU4ATAC gene, which encodes U4atac, a small nuclear RNA that is a crucial component of the minor spliceosome, were found to cause MOPD I. MOPD I is the first disease known to be associated with a defect in small nuclear RNAs. We describe here the clinical and molecular data for 17 cases of MOPD I, including 15 previously unreported cases, all carrying biallelic mutations in the RNU4ATAC gene.

Neuronal migration disorders in microcephalic osteodysplastic primordial dwarfism type I/III

Microcephalic osteodysplastic primordial dwarfism (MOPD) is a rare microlissencephaly syndrome, with at least two distinct phenotypic and genetic types. MOPD type II is caused by pericentrin mutations, while types I and III appear to represent a distinct entity (MOPD I/III) with variably penetrant phenotypes and unknown genetic basis. The neuropathology of MOPD I/III is little understood, especially in comparison to other forms of lissencephaly. Here, we report postmortem brain findings in an 11-month-old female infant with MOPD I/III. The cerebral cortex was diffusely pachygyric, with a right parietal porencephalic lesion. Histologically, the cortex was abnormally thick and disorganized. Distinct malformations were observed in different cerebral lobes, as characterized using layer-specific neuronal markers. Frontal cortex was severely disorganized and coated with extensive leptomeningeal glioneuronal heterotopia. Temporal cortex had a relatively normal 6-layered pattern, despite cortical thickening. Occipital cortex was variably affected. The corpus callosum was extremely hypoplastic. Brainstem and cerebellar malformations were also present, as well as old necrotic foci. Findings in this case suggest that the cortical malformation in MOPD I/III is distinct from other forms of pachygyria-lissencephaly.

Mechanisms regulating the development of the corpus callosum and its agenesis in mouse and human

The development of the corpus callosum depends on a large number of different cellular and molecular mechanisms. These include the formation of midline glial populations, and the expression of specific molecules required to guide callosal axons as they cross the midline. An additional mechanism used by callosal axons from neurons in the neocortex is to grow within the pathway formed by pioneering axons derived from neurons in the cingulate cortex. Data in humans and in mice suggest the possibility that different mechanisms may regulate the development of the corpus callosum across its rostrocaudal and dorsoventral axes. The complex developmental processes required for formation of the corpus callosum may provide some insight into why such a large number of human congenital syndromes are associated with agenesis of this structure.

Majewski osteodysplastic primordial dwarfism type II (MOPD II): natural history and clinical findings

A description of the clinical features of Majewski osteodysplastic primordial dwarfism type II (MOPD II) is presented based on 58 affected individuals (27 from the literature and 31 previously unreported cases). The remarkable features of MOPD II are: severe intrauterine growth retardation (IUGR), severe postnatal growth retardation; relatively proportionate head size at birth which progresses to true and disproportionate microcephaly; progressive disproportion of the short stature secondary to shortening of the distal and middle segments of the limbs; a progressive bony dysplasia with metaphyseal changes in the limbs; epiphyseal delay; progressive loose-jointedness with occasional dislocation or subluxation of the knees, radial heads, and hips; unusual facial features including a prominent nose, eyes which appear prominent in infancy and early childhood, ears which are proportionate, mildly dysplastic and usually missing the lobule; a high squeaky voice; abnormally, small, and often dysplastic or missing dentition; a pleasant, outgoing, sociable personality; and autosomal recessive inheritance. Far-sightedness, scoliosis, unusual pigmentation, and truncal obesity often develop with time. Some individuals seem to have increased susceptibility to infections. A number of affected individuals have developed dilation of the CNS arteries variously described as aneurysms and Moya Moya disease. These vascular changes can be life threatening, even in early years because of rupture, CNS hemorrhage, and strokes. There is variability between affected individuals even within the same family.

Autopsy case of microcephalic osteodysplastic primordial "dwarfism" type II

Microcephalic osteodysplastic primordial "dwarfism" (MOPD) is a group of disorders similar to Seckel syndrome. Three subtypes (types I-III) have been reported. We report here the first autopsy case of MOPD type II. The patient was a Japanese girl with typical clinical and radiological manifestations of MOPD type II. The manifestations included severe intrauterine and postnatal growth failure, microcephaly, a distinctive facial appearance, micromelia, brachytelephalangy, coxa vara, and V-shaped metaphyses of the distal femora. Other than small cerebral hemispheres, no neuropathological abnormalities were found. Chondro-osseous histology showed thinning of the growth plate, ballooned chondrocytes, reduced cellularity, lack of zonal and columnar formations, and poor formation of primary trabeculae. These findings suggest that impairment of chondrocytic formation and differentiation is the major pathogenesis of MOPD type II.

Ultrasonographic prenatal diagnosis of microcephalic osteodysplastic primordial dwarfism types I/III

Microcephalic osteodysplastic primordial dwarfism is a rare disease characterized by unique clinical appearance and specific radiographic findings, and distinctive brain abnormalities. We describe the prenatal diagnosis of two siblings with microcephalic osteodysplastic primordial dwarfism types I/III at 23 and 26 weeks of gestation, respectively. Early detection by sequential antenatal sonographic evaluation is important for counselling families known to be at risk of this rare disease.

Seckel-like syndrome in three siblings

Seckel syndrome has been described as the prototype of the primordial bird-headed type of dwarfism. Since Seckel originally defined the disorder, less than 60 cases have been reported. In addition to the characteristic craniofacial dysmorphism and skeletal defects, abnormalities have been described in the cardiovascular, hematopoietic, endocrine, and central nervous systems. This pleiotropy has implied genetic heterogeneity and prompted reviews of previously reported cases of Seckel syndrome. As a result, the characteristic diagnostic features of Seckel syndrome have been highly debated. Although deletions in chromosome 2q have been described, to date, no genetic defect has been defined. We report three cases of Seckel-like syndrome in siblings from nonconsanguinous Caucasian parents. In addition to the typical Seckel phenotypic features, all three cases were characterized by severe hydrocephalus. We review the literature and propose that there is a spectrum of Seckel conditions that share some common key features, but also demonstrate a wide range of phenotypic features.

Neonatal cholestasis and focal medullary dysplasia of the kidneys in a case of microcephalic osteodysplastic primordial dwarfism

We report on a male infant who presented with intrauterine growth retardation, severe postnatal failure to thrive, microcephaly, facial dysmorphism, and skeletal dysplasia. The clinical and radiological findings are consistent with former descriptions of microcephalic osteodysplastic primordial dwarfism (MOPD) type I/III. In addition to previously published features, multiple fractures of the long bones, severe neonatal cholestasis, and histological dysplasia of the kidneys were found. The boy died at the age of 8 months. The new finding of focal renal medullary dysplasia further supports the hypothesis of a basic defect in tissue differentiation in the pathogenesis of this rare condition.

[Bird headed dwarfism in Seckel syndrome. Nosologic difficulties]

Seckel syndrome is a clinical picture which associates four main features: intrauterine growth retardation, microcephaly often due to craniosynostosis, orofacial dysmorphology with bird headed appearance and variable mental retardation which is present after several months. Malformations of the central nervous system, limbs, and hair, may also be observed. On the basis of 78 cases reported in the literature, the authors discuss the validity of the morphological features of the syndrome. It is likely that the variability in the expressivity of each symptom explains its heterogeneity. According to the radiological abnormalities, three different forms of the syndrome have been described. Seckel syndrome is a genetic disorder with autosomal recessive inheritance. Its ethiopatogeny remains unclear. Hopefully linkage studies will allow to map the gene in order to determine the underlying abnormal protein.

Microcephalic, osteodysplastic, primordial dwarfism

A case of microcephalic, osteodysplastic, primordial dwarfism (cephaloskeletal dysplasia of Taybi and Linder) is reported. This rare disease is characterised by unique clinical appearances and diagnostic radiographic findings. It is also associated with distinctive brain abnormalities. The latter include micrencephaly, lissencephaly, corpus callosum aplasia/agenesis and unusual histological brain abnormalities.

Intrauterine growth retardation and familial short stature

Intrauterine growth retardation (IUGR) is an important cause of small stature in children presenting to paediatric endocrinologists. IUGR has to be differentiated from familial ('constitutional') short stature, where the growth deficit is genetically determined and/or induced by smallness of the mother (maternal constraint). Intrinsic fetal anomalies such as chromosomal abnormalities, primary growth failure syndromes, congenital infections and congenital anomalies are of equal importance with maternal disorders, in particular chronic use of alcohol, tobacco and narcotics, and pregnancy complications like hypertension and pre-eclampsia, in causing fetal growth retardation. The relative importance of placental abnormalities and environmental factors (with the exception of malnutrition) appears to be small. Some catch-up growth of children with IUGR has been observed in about 70% of all cases during the first year of life. Many IUGR children show major or minor birth defects which may be predisposing factors or may also coexist because of common underlying factors producing both small stature and structural anomalies. Since in most children with IUGR adult heights to be expected are below the population range, growth hormone treatment has been tried for many years, but the data available from the literature are not encouraging to date and need to be re-evaluated in controlled long-term trials.

Microcephalic osteodysplastic primordial dwarfism type I/III in sibs

The clinical and radiological findings in a pair of sibs with microcephalic osteodysplastic primordial dwarfism (MOPD) are described, a boy who survived for 5 1/2 years and his more severely affected younger sister, who died at the age of 6 months. Neuropathological studies in this girl showed marked micrencephaly with severely hypoplastic, poorly gyrated frontal lobes and absent corpus callosum. Our observation supports the hypothesis that types I and III MOPD probably constitute a spectrum of one and the same entity and published data together with this report are consistent with autosomal recessive inheritance. The pathogenesis of this condition is as yet unknown, but its characteristics indicate a basic defect affecting cell proliferation and tissue differentiation.

Osteodysplastic variant of primordial dwarfism

A patient with intrauterine growth retardation and marked postnatal retardation of growth had microcephaly and the orofacial and dental characteristics of the Seckel phenotype. In addition she had short forearms, metaphyseal flare, especially of the distal femora, triangular distal femoral epiphyses, and pseudoepiphyses of the hands, all characteristics of an osteodysplastic variant. Parental consanguinity suggests autosomal recessive inheritance.

Primordial osteodysplastic dwarfism type I in association with corneal clouding: evidence for autosomal recessive inheritance

A newborn male, born to Turkish first cousins, presented with severe pre- and postnatal growth retardation. Weight was 800 g at term. Salient clinical features were dwarfism with moderate limb shortening, microcephaly, hirsutism, facial dysmorphism including prominent small cloudy eyes, large nose with high nasal root, retrognathism and low-set ears. Radiologic abnormalities included huge clavicles, dysplastic vertebrae and enlargement of proximal metaphyses with medial spurs.