David D. Weaver

A recurrent 16p12.1 microdeletion supports a two-hit model for severe developmental delay

We report the identification of a recurrent, 520-kb 16p12.1 microdeletion associated with childhood developmental delay. The microdeletion was detected in 20 of 11,873 cases compared with 2 of 8,540 controls (P = 0.0009, OR = 7.2) and replicated in a second series of 22 of 9,254 cases compared with 6 of 6,299 controls (P = 0.028, OR = 2.5). Most deletions were inherited, with carrier parents likely to manifest neuropsychiatric phenotypes compared to non-carrier parents (P = 0.037, OR = 6). Probands were more likely to carry an additional large copy-number variant when compared to matched controls (10 of 42 cases, P = 5.7 × 10−5, OR = 6.6). The clinical features of individuals with two mutations were distinct from and/or more severe than those of individuals carrying only the co-occurring mutation. Our data support a two-hit model in which the 16p12.1 microdeletion both predisposes to neuropsychiatric phenotypes as a single event and exacerbates neurodevelopmental phenotypes in association with other large deletions or duplications. Analysis of other microdeletions with variable expressivity indicates that this two-hit model might be more generally applicable to neuropsychiatric disease.

Wiedemann-Beckwith syndrome: presentation of clinical and cytogenetic data on 22 new cases and review of the literature

SummaryThe main features of Wiedemann-Beckwith syndrome (WBS) include macroglossia, abdominal wall defects, visceromegaly, gigantism, hypoglycemia, ear creases, nevus flammeus, and mid-face hypoplasia. Twenty-two cases of WBS were examined clinically and cytogenetically, and compared to 226 previously reported cases. Aspects of the clinical evaluations are discussed. All individuals examined were chromosomally normal with no evidence of 11p abnormality as has been reported recently. The relevance of a possible relationship between clinical findings, chromosome abnormalities, and genes present on 11p is discussed. Transmission of this condition is most consistent with autosomal dominant inheritance with incomplete penetrance.

Mutations in EZH2 Cause Weaver Syndrome

We used trio-based whole-exome sequencing to analyze two families affected by Weaver syndrome, including one of the original families reported in 1974. Filtering of rare variants in the affected probands against the parental variants identified two different de novo mutations in the enhancer of zeste homolog 2 (EZH2). Sanger sequencing of EZH2 in a third classically-affected proband identified a third de novo mutation in this gene. These data show that mutations in EZH2 cause Weaver syndrome.

Familial variation of head size and adjustment for parental head circumference

Occipitofrontal head circumference was measured on 122 twin pairs, their spouses, and their children. These data indicate that approximately 50% of normal head size variation is familial. Because of the relationship between the head size of normal children and their parents, adjustment of a childs head size value by the average parental value permits better definition of the range of normalcy. A method is presented that will allow physicians to make this adjustment, providing a more refined assessment of head size when there is a suspected abnormality.

Mutations in PIEZO2 Cause Gordon Syndrome, Marden-Walker Syndrome, and Distal Arthrogryposis Type 5

Gordon syndrome (GS), or distal arthrogryposis type 3, is a rare, autosomal-dominant disorder characterized by cleft palate and congenital contractures of the hands and feet. Exome sequencing of five GS-affected families identified mutations in piezo-type mechanosensitive ion channel component 2 (PIEZO2) in each family. Sanger sequencing revealed PIEZO2 mutations in five of seven additional families studied (for a total of 10/12 [83%] individuals), and nine families had an identical c.8057G>A (p.Arg2686His) mutation. The phenotype of GS overlaps with distal arthrogryposis type 5 (DA5) and Marden-Walker syndrome (MWS). Using molecular inversion probes for targeted sequencing to screen PIEZO2, we found mutations in 24/29 (82%) DA5-affected families and one of two MWS-affected families. The presence of cleft palate was significantly associated with c.8057G>A (Fishers exact test, adjusted p value < 0.0001). Collectively, although GS, DA5, and MWS have traditionally been considered separate disorders, our findings indicate that they are etiologically related and perhaps represent variable expressivity of the same condition.

Distal 13q deletion syndrome and the VACTERL Association : Case report, literature review, and possible implications

We present a case of a child with del(13) (q31.1qter), VACTERL association, and penoscrotal transposition. Deletion of the distal long arm of chromosome 13 is associated with variable phenotypes. These phenotypes are divided into three clusters; each cluster represents a specific deleted segment of 13q. Individuals with deletions of a critical region at 13q32 have multiple congenital malformations that include components of the VACTERL association. Our patient had all six manifestations of VACTERL association. In addition, he had complete penoscrotal transposition, a unique malformation reported rarely in VACTERL association and only twice previously in deletion of distal 13q. We reviewed all reported cases of distal 13q deletions to date. Of these 137 patients, 15 could be classified into the VACTERL association. Ours was the only patient with distal 13q deletion and all VACTERL association features and also the only one with tracheoesophageal fistula. Neither holoprosencephaly nor the other central nervous system malformations that have been seen in individuals with distal 13q deletions were apparent in him. The patient presented here appears to be unique among individuals with distal 13q deletion. His cluster of malformations strengthens the argument that distal 13q deletion is a cause for VACTERL association, and that this causal relationship implies a syndromic form of VACTERL. In addition, this case and those ascertained from the literature suggest that penoscrotal transposition should be considered part of both the distal 13q-deletion syndrome and some forms of VACTERL association.

Identification of familial and de novo microduplications of 22q11.21-q11.23 distal to the 22q11.21 microdeletion syndrome region

Deletions of the 22q11.2 region distal to the 22q11.21 microdeletion syndrome region have recently been described in individuals with mental retardation and congenital anomalies. Because these deletions are mediated by low-copy repeats (LCRs), located distal to the 22q11.21 DiGeorge/velocardiofacial microdeletion region, duplications are predicted to occur with a frequency equal to the deletion. However, few microduplications of this region have been reported. We report the identification of 18 individuals with microduplications of 22q11.21-q11.23. The duplication boundaries for all individuals are within LCRs distal to the DiGeorge/velocardiofacial microdeletion region. Clinical records for nine subjects reveal shared characteristics, but also several examples of contradicting clinical features (e.g. macrocephaly versus microcephaly and upslanting versus downslanting palpebral fissures). Of 12 cases for whom parental DNA samples were available for testing, one is de novo and 11 inherited the microduplication from a parent, three of whom reportedly have learning problems or developmental delay. The variable phenotypes and preponderance of familial cases obfuscate the clinical relevance of the molecular data and emphasize the need for careful parental assessments and clinical correlations.

Congenital contractural arachnodactyly. Report of four additional families and review of literature.

We report here four families with congenital contractural arachnodactyly (CCA) in which a wide range of phenotypic expression is observed. In one family with a large number of affected individuals the condition is mildly expressed. These individuals usually have crumpled ears, camptodactyly with ulnar deviation of the fingers, adducted thumbs, limited elbow and/or knee extension, and hypoplasia of the calf muscles. Arachnodactyly is not a constant feature. No spinal deformities are present and only the proband has clubfoot deformities. With time, affecteds have experienced spontaneous improvement of their contractures and their condition in adulthood has not interfered with a normal lifestyle. Within this family there is little phenotypic variation between affected individuals. Those affected within each of the other families have had varying degrees of severity of the condition. A review of 29 other kindreds described in the literature with congenital contractural arachnodactyly shows that in this condition the most common features are abnormally formed ears, camptodactyly, arachnodactyly, adducted thumbs, limited movement of the elbows and knees, and underdevelopment of the calf muscles. Spontaneous improvement of the contractures with age is reported in 94% of cases. Kyphosis, scoliosis or kyphoscoliosis occurred in 50% and these defects were present in those who where more severely affected with CCA. No ocular problems have been reported in this syndrome, but congenital heart defects have occurred in 14.7%. Marfan syndrome is the most important condition to differentiate from congenital contractural arachnodactyly since these two conditions are similar phenotypically. However, in the former there are frequently serious ocular and cardiovascular problems which lead to significant morbidity and/or early death.

Mild autosomal dominant hypophosphatasia: In utero presentation in two families

We describe four pregnancies in two families in which mild hypophosphatasia, apparently transmitted as an autosomal dominant trait, manifested in utero as severe long bone bowing. Postnatally, there was spontaneous improvement of the skeletal defects. Recognition of this presentation for hypophosphatasia by family investigation and assessment of the fetal skeleton for degree of ossification and chest size using ultrasonography is important. The prognosis for this condition is considerably better than for more severe forms of hypophosphatasia and for many other disorders that cause skeletal defects with long bone bowing in utero.

Oculo-auriculo-vertebral spectrum and the CHARGE association: clinical evidence for a common pathogenetic mechanism.

We describe two infants with features of both the oculo-auriculo-vertebral spectrum (OAVS) and the CHARGE association (CA) Both patients are more severely affected than the typical patient with the OAVS Each has facial asymmetry, mandibular hypoplasia, ear abnormalities, hearing impairment, microphthalmia, heart defects, and developmental delay. They, also have features that are not characteristic of either OAVS or CA including torticollis, plagiocephaly, and heminostril. Based on the findings of these patients and others reported in the literature, there appears to be a significant overlap of features between OAVS and CA. and we suggest that these conditions in fact may be produced by the same pathogenetic mechanism. One such mechanism to explain the overlap of these disorders is that both conditions are part of the axial mesodermal spectrum, and represent a dysblastogenetic process. This mechanism may also explain the presence of some of the additional features not normally seen in OAVs and CA but seen in these two infants.