Laurie S. Sadler

Molecular and Clinical Analyses of Greig Cephalopolysyndactyly and Pallister-Hall Syndromes: Robust Phenotype Prediction from the Type and Position of GLI3 Mutations

Mutations in the GLI3 zinc-finger transcription factor gene cause Greig cephalopolysyndactyly syndrome (GCPS) and Pallister-Hall syndrome (PHS), which are variable but distinct clinical entities. We hypothesized that GLI3 mutations that predict a truncated functional repressor protein cause PHS and that functional haploinsufficiency of GLI3 causes GCPS. To test these hypotheses, we screened patients with PHS and GCPS for GLI3 mutations. The patient group consisted of 135 individuals: 89 patients with GCPS and 46 patients with PHS. We detected 47 pathological mutations (among 60 probands); when these were combined with previously published mutations, two genotype-phenotype correlations were evident. First, GCPS was caused by many types of alterations, including translocations, large deletions, exonic deletions and duplications, small in-frame deletions, and missense, frameshift/nonsense, and splicing mutations. In contrast, PHS was caused only by frameshift/nonsense and splicing mutations. Second, among the frameshift/nonsense mutations, there was a clear genotype-phenotype correlation. Mutations in the first third of the gene (from open reading frame [ORF] nucleotides [nt] 1-1997) caused GCPS, and mutations in the second third of the gene (from ORF nt 1998-3481) caused primarily PHS. Surprisingly, there were 12 mutations in patients with GCPS in the 3 third of the gene (after ORF nt 3481), and no patients with PHS had mutations in this region. These results demonstrate a robust correlation of genotype and phenotype for GLI3 mutations and strongly support the hypothesis that these two allelic disorders have distinct modes of pathogenesis.

Mutations in the Gene Encoding the Calcium-Permeable Ion Channel TRPV4 Produce Spondylometaphyseal Dysplasia, Kozlowski Type and Metatropic Dysplasia

The spondylometaphyseal dysplasias (SMDs) are a group of short-stature disorders distinguished by abnormalities in the vertebrae and the metaphyses of the tubular bones. SMD Kozlowski type (SMDK) is a well-defined autosomal-dominant SMD characterized by significant scoliosis and mild metaphyseal abnormalities in the pelvis. The vertebrae exhibit platyspondyly and overfaced pedicles similar to autosomal-dominant brachyolmia, which can result from heterozygosity for activating mutations in the gene encoding TRPV4, a calcium-permeable ion channel. Mutation analysis in six out of six patients with SMDK demonstrated heterozygosity for missense mutations in TRPV4, and one mutation, predicting a R594H substitution, was recurrent in four patients. Similar to autosomal-dominant brachyolmia, the mutations altered basal calcium channel activity in vitro. Metatropic dysplasia is another SMD that has been proposed to have both clinical and genetic heterogeneity. Patients with the nonlethal form of metatropic dysplasia present with a progressive scoliosis, widespread metaphyseal involvement of the appendicular skeleton, and carpal ossification delay. Because of some similar radiographic features between SMDK and metatropic dysplasia, TRPV4 was tested as a disease gene for nonlethal metatropic dysplasia. In two sporadic cases, heterozygosity for de novo missense mutations in TRPV4 was found. The findings demonstrate that mutations in TRPV4 produce a phenotypic spectrum of skeletal dysplasias from the mild autosomal-dominant brachyolmia to SMDK to autosomal-dominant metatropic dysplasia, suggesting that these disorders should be grouped into a new bone dysplasia family.

Carotid ultrasound examination in Williams syndrome.

OBJECTIVEnTo noninvasively measure arterial wall thickness in a group of patients with Williams syndrome (WS).nnnMETHODSnHigh-resolution, real-time B-mode ultrasonography was used to examine the carotid arteries of 20 patients with WS (ages 7 months to 24.9 years) and 25 control subjects (ages 2.5 years to 25.5 years).nnnRESULTSnThe mean combined intimal-medial wall thickness of the patients in the WS group was 0.86 mm +/- 0.08 mm compared with a mean of 0.54 mm +/- 0.05 mm in the control subjects (p < 0.0001). Within the WS group, arterial wall thickness did not vary significantly with gender, patient age, the presence or absence of stenotic cardiac disease, or the presence or absence of hypertension.nnnCONCLUSIONSnThe ultrasonographic finding of increased carotid arterial wall thickness across a wide range of patients with WS demonstrates the pervasive nature of the arteriopathy of this disorder. That increased arterial wall thickness was observed in all patients studied suggests that the arteriopathy of WS is related to haploinsufficiency for the elastin gene.

Early puberty in Williams syndrome.

Pubertal development was evaluated in nine males and 16 females with Williams syndrome (WS). Our results indicate that puberty in WS occurred earlier than in published population controls; specifically, 90% of menstruating females reached menarche and 83% of pubertal males showed Tanner III pubic hair development prior to the age of 12 years. The sequence of pubertal development was normal, bone age was always consistent with, or in excess of, chronological age, and there was evidence of central (hypothalamic-pituitary mediated) activation as the cause of early puberty in a subset of subjects.

Delay in Diagnosis of Williams Syndrome

Williams syndrome (WS) is a well-known genetic disorder with a variable phenotype. In many cases, physical manifestations are subtle and may not be apparent at an early age, making diagnosis difficult in infants and young children who lack classic manifestations such as supravalvular aortic stenosis and hypercalcemia. Clinical suspicion is essential because the diagnostic genetic finding is not detectable on routine chromosomal analysis. Furthermore, early diagnosis allows for earlier detection and treatment of developmental, behavioral, and medical problems. In an effort to understand how and why individuals with WS are diagnosed, we conducted a survey-based study of parents of WS children. Packets containing a cover letter, consent form, parental survey and preaddressed stamped envelope were distributed to parents of children with WS. The survey included questions concerning initial diagnosis, WS findings present, medical specialists involved, and tests performed. Forty-six completed surveys were returned for analysis. The mean age at diagnosis was 3.66 years (SD 4.13). The mean age at which there were initial concerns was 0.98 year (SD 1.24) resulting in a mean delay in diagnosis of 2.77 years (SD 4.10). In addition, the involvement of a geneticists correlated with earlier diagnosis (2.26 years vs. 5.09 years without geneticist involvement, p = 0.03) and fewer tests ordered (5.2 vs. 8.2 in the nongeneticist group, p=0.0006). We observed a significant delay in the diagnosis of WS. Of note, the involvement of a geneticist was associated with earlier diagnosis and reduced number of tests.

Reduced stereoacuity in Williams syndrome

Strabismus is a frequently recognized manifestation of Williams syndrome [Greenberg and Lewis, 1988: Ophthalmology 95:1608-1612; Kapp et al., 1995: Am J Ophthalmol 119:355-360]. We recently evaluated the ophthalmologic function of 12 patients with Williams syndrome (WS), with an emphasis on binocularity. Four of 12 patients (33%) had measurable strabismus. Of the 8 remaining patients, examination of binocular function was possible in 6, all of whom demonstrated reduced stereoacuity. We speculate that subnormal binocular vision and the poor visuospatial performance observed in patients with WS may be related to abnormal brain morphogenesis in the region of the occipitoparietal cortex.

Subnormal binocular vision in the Williams syndrome.

PURPOSEnPatients with Williams syndrome have been found to have a high prevalence of strabismus. This may be due to a primary sensory abnormality. The purpose of this study was to determine the prevalence of subnormal binocular vision in patients with Williams syndrome.nnnMETHODSnPatients being followed in an interdisciplinary Williams syndrome clinic were prospectively evaluated to determine their binocular status.nnnRESULTSnEleven patients with Williams syndrome underwent an ophthalmologic evaluation. Twenty-seven percent of patients had strabismus (3/11). Eight patients demonstrated no measurable strabismus. Six of these patients were found to have monofixation syndrome.nnnCONCLUSIONSnThere is a high prevalence of subnormal binocular vision in Williams syndrome. This subnormal binocular vision may explain the high prevalence of strabismus in this syndrome.