Microcephalic Osteodysplastic Primordial Dwarfism, Type Ii

A number sign (#) is used with this entry because microcephalic osteodysplastic primordial dwarfism type II (MOPD2) is caused by homozygous or compound heterozygous mutation in the PCNT gene (605925), encoding pericentrin, on chromosome 21q22.

Description

Microcephalic osteodysplastic primordial dwarfism type II is characterized by intrauterine growth retardation, severe proportionate short stature, and microcephaly. It is distinct from Seckel syndrome (see 210600) by more severe growth retardation, radiologic abnormalities, and absent or mild mental retardation (summary by Willems et al., 2010).

Clinical Features

In 3 unrelated children, Majewski et al. (1982) described a form of intrauterine and postnatal dwarfism with microcephaly and facial features resembling those of Seckel syndrome (see 210600) but with anomalies of bones: disproportionate shortness of forearms and legs in the first years of life, brachymesophalangy, brachymetacarpy I, V-shaped flare of at least the distal femoral metaphyses, triangular shape of the distal femoral epiphyses, high and narrow pelvis, proximal femoral epiphysiolysis, and coxa vara. They pointed to seemingly identical cases reported by Brizard et al. (1973) and Anoussakis et al. (1974). All 5 cases were sporadic. Majewski (1982) suggested that this might be the same as the Taybi-Linder syndrome (MOPD1; 210710). Willems et al. (1987) reported what they presumed to be the sixth case in a child of consanguineous parents. The genetics may be clarified by the findings of Verloes et al. (1987) who observed male and female affected sibs, the offspring of first-cousin parents. One of the affected sibs reported by Verloes et al. (1987) was a twin. Inasmuch as the other twin was unaffected, a photograph of the twins demonstrated the abnormality dramatically.

Sugio et al. (1993) reported a case. The mother was short, with a small head and disproportionately short forearms and legs, for which reason Sugio et al. (1993) suggested dominant inheritance. It would seem equally likely that the mother was a manifesting heterozygote.

Al Gazali et al. (1995) reported a typical case of the syndrome in a girl of Baluch origin. Complex consanguinity in this family confirmed autosomal recessive inheritance of the disorder.

This disorder was mentioned as a possibility in the case of 2 African American brothers who had microcephaly, short stature, and generalized microdontia (Lin et al., 1995). The face was not typical of Seckel syndrome. Radiographic features of the skeleton were mild, yet growth was severely delayed.

Masuno et al. (1995) described a 22-month-old Japanese girl with microcephaly, prominent nose, pre- and postnatal dwarfism, increased intraocular pressure, mesomelic shortening of the legs, brachydactyly, multiple pseudoepiphyses in the bases of the metacarpals, coxa valga, wide pelvis with iliac flaring, disharmonious maturation of the epiphyses, and patent cranial sutures. The girl resembled children with osteodysplastic primordial dwarfism II, although she did not have mesomelic shortening of the forearms, metaphyseal flaring, or typical narrow pelvis. Masuno et al. (1995) could not exclude the possibility that this case represented a new variant of osteodysplastic primordial dwarfism.

Halder et al. (1998) described a 7-year-old boy with osteodysplastic primordial dwarfism type II with normal intellect but delayed myelination on brain MRI.

Majewski and Goecke (1998) reported 3 new cases of MOPD II and reviewed 14 published cases. All children had marked intrauterine and postnatal growth failure, disproportionate microcephaly, and mental retardation. They were disproportionately short statured due to short limbs. Characteristic skeletal anomalies included small iliac wings with flat acetabular angles, coxa vara, V-shaped distal femoral metaphyses, and triangular distal femoral epiphyses, as well as metacarpal pseudoepiphyses, short first metacarpals, and brachymesophalangy V. One of their cases developed bilateral epiphysiolysis of the femoral heads at age 3. Majewski and Goecke (1998) commented that the cases of Sugio et al. (1993) probably represent another type of intrauterine growth retardation, as neither the mother nor the child was as small as in MOPD II and the mother's intellect was normal.

Fukuzawa et al. (2002) reported the autopsy findings in a Japanese girl with typical clinical and radiologic features of MOPD II. The manifestations included severe intrauterine and postnatal growth failure, microcephaly, a distinctive facial appearance, micromelia, brachytelephalangy, coxa vera, and V-shaped metaphyses of the distal femurs. Other than small cerebral hemispheres, no neuropathologic abnormalities were found. Chondroosseous 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 suggested that impairment of chondrocytic formation and differentiation is the major pathogenesis of MOPD II.

Fukuzawa et al. (2002) compared the pathology of Seckel syndrome with that of MOPD types I (210710), II, and III (210730).

Hall et al. (2004) reviewed the clinical features of MOPD II on the basis of 58 affected individuals (27 from the literature and 31 previously unreported cases). The remarkable features of MOPD II were found to be severe intrauterine growth retardation (IUGR) and 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 that appear prominent in infancy and early childhood, ears that 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. Hyperopia, scoliosis, unusual pigmentation, and truncal obesity often develop with time. Some individuals seem to have increased susceptibility to infections. There was variability between affected individuals even within the same family. Useful clinical photographs were provided.

Piane et al. (2009) reported a 3-year-old Italian boy who had prenatal onset of proportionate dwarfism, postnatal severe microcephaly, high forehead with receding hairline, sparse scalp hair, beaked nose, mild retrognathia, and hypotonia, who was diagnosed at birth with Seckel syndrome. At age 3 years, he developed paresis of the right arm due to stenosis of the median cerebral artery. X-ray examination showed high iliac wings, narrow ischia and pubis, overtubulated long bones, delta-shaped distal femoral metaphyses with marked widening, brachytelemesophalangia, and delayed bone age. Given the proportionate head size at birth, subsequent growth retardation, cerebrovascular abnormalities, and evidence for skeletal dysplasia, the diagnosis was changed from Seckel to MOPD II.

Clinical Variability

In a Thai brother and sister, Kantaputra (2002) described a syndrome of proportionate primordial short stature, severe microdontia with opalescent teeth and rootless molars, severely hypoplastic alveolar bone, large sella turcica, and slender and straight clavicles with hypoplastic scapulae. Facial features included large nose with prominent nasal bridge and small pinnae. There were areas of hypo- and hyperpigmentation that did not follow Blaschko lines, and the scalp hair was dry and thin. Intelligence and hearing were normal. Both sibs had narrow chests and pelvises, decreased elbow extension, distal symphalangism of toes, and brachymesophalangy of fingers. Radiographic features of the hands and wrists included ivory and cone-shaped epiphyses that usually disappeared with age and angular scaphoid and trapezium bones.

Kantaputra et al. (2004) reported 2 Thai children, male and female third cousins, with the same syndrome as the brother and sister reported by Kantaputra (2002). Features of microcephalic osteodysplastic primordial dwarfism included intrauterine growth retardation (IUGR), microcephaly, prominent nose and nasal bridge, small pinnae, short stature, cone-shaped and ivory epiphyses, delayed bone age, slender long bones, and abnormal pelvis. Additional features pointing to a distinct syndrome, which the authors designated 'MOPD with tooth abnormalities,' consisted of severe microdontia, malformed teeth, single-rooted or rootless teeth, severely hypoplastic alveolar bone, cafe-au-lait spots, acanthosis nigricans, and areas of hypo- and hyperpigmented skin.

Hall (2005) argued that the patients reported by Kantaputra (2002) and Kantaputra et al. (2004) as having a distinct entity, MOPD with tooth anomalies, in fact had classic MOPD II. Kantaputra and Tanpaiboon (2005) responded that although the disorders may be allelic, the microdontia in those patients 'was severe beyond the spectrum of MOPD type II.'

Kantaputra et al. (2011) provided follow-up on the 2 unrelated Thai families with MOPD and tooth anomalies, previously reported by Kantaputra (2002) and Kantaputra et al. (2004). The brother and sister reported in 2002, now 26 and 24 years old, respectively, were healthy except for MOPD II-related features. The brother had lost all of his permanent teeth, whereas the sister had 5 remaining permanent teeth with 1 unerupted right mandibular premolar, and in both sibs the alveolar bone was severely hypoplastic. Reevaluation at ages 12 and 10 years, respectively, of the cousins reported in 2004 showed that primary teeth were of normal size but permanent teeth were extremely small, measuring 2 mm to 2.5 mm mesiodistally. The authors commented that the teeth were 'probably the smallest ever reported.' All first permanent molars, however, were of normal size but rootless. The male cousin died of unknown cause at 11 years of age; the girl was otherwise healthy. All 4 patients had skin that was hypo- and hyperpigmented, dry, and appeared darker as they aged; multiple creases were present on the palms and soles. After molecular analysis revealed mutations in the PCNT gene in affected individuals from both families (see MOLECULAR GENETICS), Kantaputra et al. (2011) concluded that the severe microdontia and alveolar bone hypoplasia in these patients, which seemed to indicate a distinct syndrome, instead represented the variability of the MOPD II phenotype.

Other Features

Nishimura et al. (2003) described a 4-year-old boy with MOPD II and cafe-au-lait spots who developed left hemiparesis and seizures and was found to have moyamoya disease (see 607151) on MRI, with infarction of the right cerebral hemisphere. FISH analysis of the NF1 gene (613113) at 17q11.2 did not show any deletions, and the boy had no neurofibromas or Lisch nodules. Young et al. (2004) reported a second patient with MOPD II, cafe-au-lait spots, and moyamoya disease. She began having episodes of weakness and seizures at age 2.5 years; cerebral angiography revealed typical 'moyamoya' vessels and MRI showed multiple areas of cerebral infarction. Standard karyotyping, specific sister chromatid exchange and diepoxy chromosome breakage analysis, and mitochondrial mutation testing were normal. Young et al. (2004) suggested that the list of moyamoya disease associations should be extended to include the unusual combination of MOPD II with multiple cafe-au-lait spots.

In a review of 58 individuals with MOPD II, Hall et al. (2004) noted that 11 (19%) affected individuals had developed dilation of the CNS arteries variously described as aneurysms and moyamoya disease. These vascular changes can be life threatening, even in early years, because of rupture, CNS hemorrhage, and strokes.

Brancati et al. (2005) reported a 2-year-old boy with MOPD II who developed left hemiparesis and was found on CT scan to have a right anterior cerebral ischemic lesion and cerebrovascular anomalies consistent with moyamoya disease. The authors reviewed published patients with cerebrovascular anomalies who had received a diagnosis of Seckel syndrome or MOPD II, and they concluded that such anomalies are preferentially associated with MOPD II, affecting 15 (23.8%) of 63 published MOPD II patients. Hall (2006) commented on the report of Brancati et al. (2005) and suggested that there may be a premature aging process in the vessels of affected individuals in addition to abnormalities in vessel formation.

Bober et al. (2010) reported that 13 (52%) of 25 patients in an MOPD II registry had cerebral neurovascular abnormalities. Eight of the 13 were male, suggesting a male predominance. Four patients were reported in detail. One patient was a 3-year-old boy who showed progressive worsening of moyamoya disease on serial brain imaging studies. He was asymptomatic, but had ischemic lesions of the frontal lobe and was successfully treated with encephalo-duro-arterio-synangiosis (EDAS). The second patient presented at age 16 years with severe headache and projectile vomiting due to a ruptured aneurysm; he was found to have accompanying moyamoya angiopathy and was treated with clipping of the aneurysm and EDAS. Although he recovered well, he was noted to have mildly impaired cognitive development. The most severely affected patient had moyamoya disease detected at age 13 years, followed by EDAS. However, later in his teens he developed chest pain associated with calcification and hypoplasia of the left anterior descending coronary artery, as well as a subarachnoid hemorrhage due to an aneurysm. An acute coronary event in his late teens necessitated angioplasty and stenting. The last patient had evidence of moyamoya disease at age 11 years. At age 14, he showed cognitive and behavioral decline, and repeat imaging showed progression of moyamoya disease, resulting in treatment with EDAS. Bober et al. (2010) noted a general pattern in progression of the cerebrovascular changes, from stenosis to occlusion, mainly affecting the circle of Willis and presumably resulting from smooth muscle proliferation in affected arteries. Bober et al. (2010) emphasized the need for a standardized screening program occurring at 12- to 18-month intervals in patients with MOPD II.

Mapping

Rauch et al. (2008) performed homozygosity mapping with 3 consanguineous families with MOPD II. Genomewide linkage analysis using polymorphic short tandem repeat markers revealed a single disease locus on chromosome 21q22.3 with the first 2 families. When a third family was included, the lod score for linkage was 3.7 with marker D21S1446.

Molecular Genetics

Rauch et al. (2008) determined that biallelic loss-of-function mutations in the PCNT gene cause MOPD II. They identified 29 different mutations in the PCNT gene in 25 patients with MOPD II (see., e.g., 605925.0004-605925.0008). There were 12 stop mutations and 17 frameshift mutations and all patients were homozygous or compound heterozygous, consistent with autosomal recessive inheritance. Rauch et al. (2008) found that both investigated heterozygous parents of one patient showed reduced protein levels in lymphoblasts and postulated that this might explain their finding of significant reduction of the mean height of heterozygous MOPD II parents.

Willems et al. (2008) noted that mutations in the PCNT gene had been identified in 28 patients, including the 25 with MOPD II reported by Rauch et al. (2008) and the 3 diagnosed with Seckel syndrome reported by Griffith et al. (2008). They performed direct sequencing of PCNT in 21 patients and identified 9 distinct mutations in 4 of the 16 patients diagnosed with Seckel syndrome and in all 5 patients diagnosed with MOPD II. Clinical analysis of the 4 Seckel syndrome patients with PCNT mutations showed that all presented minor skeletal changes and a severe growth retardation more suggestive of MOPD II. Willems et al. (2008) concluded that, despite variable clinical severity, MOPD II is a genetically homogeneous condition due to loss of function of pericentrin. Thus, the patients reported by Griffith et al. (2008) with mutations in the PCNT gene (605925.0001-605925.0003) can be considered to have MOPD II. In their full report, in which additional patients were studied, Willems et al. (2010) identified a total of 13 distinct mutations in the PCNT gene, including one in another patient diagnosed with Seckel syndrome (605925.0009); this patient also had minor skeletal changes and clinical features compatible with a diagnosis of MOPD II.

In 4 patients from 2 unrelated Thai pedigrees with features of MOPD II as well as extreme microdontia and alveolar bone hypoplasia, originally reported by Kantaputra (2002) and Kantaputra et al. (2004), Kantaputra et al. (2011) analyzed the PCNT gene and identified compound heterozygosity for 2 mutations in the brother and sister (605925.0004 and 605925.0010), and homozygosity for a nonsense mutation in the cousins (605925.0011). Although the phenotype in these patients was initially designated as a new syndrome, Kantaputra et al. (2011) stated that these patients represented the phenotypic variability of MOPD II.

History

Hall et al. (2004) described the history of clinical descriptions of MOPD II in the medical literature and reviewed historic cases beginning with Lucia Zarate, who was born in Mexico in 1864, was 7 inches long at birth, and 20 inches in height at the age of 12 years. She worked for the Barnum and Bailey circus for many years as one of its major attractions. She was described as cheerful, loquacious, and beloved by the circus troupe. She was reported to have died of exposure in a snow storm at the age of 26 years when the circus train on which she was traveling tried to cross the Rocky Mountains and became stuck in the snow.

Karasik et al. (1992) suggested that the MOPD2 locus may be on chromosome 1. They described a moderately retarded 11-year-old girl who appeared to have this disorder and showed deletion of 1q21-q24.