Clinical and functional properties of novel VHL mutation (X214L) consistent with Type 2A phenotype and low risk of renal cell carcinoma.

This report describes clinical characteristics in families with a Type 2A phenotype and functional properties of a novel von Hippel Lindau variant (X214L). Pedigrees were analyzed. Analysis of von Hippel Lindau (VHL) coding exons and flanking intronic sequences in DNA from a proband with pheochromocytoma and islet cell tumor was performed. Western blot assays for VHL protein (pVHL), HIFα, and Jun B were conducted using VHL null renal clear carcinoma cell lines that were engineered to produce wild-type or X214L mutant pVHL. Pedigree analysis indicated that the variant tracked with disease and the same or similar VHL point mutations were identified in several Type 2A families. The predicted 14 amino acid extended pVHL variant, when reintroduced into VHL null cells, was stable and retained the ability to downregulate HIFα in a hydroxylationdependent manner. In contrast, the variant was defective with respect to downregulation of JunB. pVHL X214L, like other pVHL variants associated with a low risk of clear cell renal carcinoma, largely preserves the ability to downregulate HIF. In contrast, this variant, like other pVHL variants linked to Type 2A disease, fails to suppress JunB. This underscores that JunB may play a role in the pathogenesis of Type 2A VHL disease.

Scanning for telomeric deletions and duplications and uniparental disomy using genetic markers in 120 children with malformations.

We screened 120 children with sporadic multiple congenital anomalies and either growth or mental retardation for uniparental disomy (UPD) or subtelomeric deletions. The screening used short tandem repeat polymorphisms (STRP) from the subtelomeric regions of 41 chromosome arms. Uninformative marker results were reanalyzed by using the next available marker on that chromosome arm. In total, approximately 25,000 genotypes were generated and analyzed for this study. Subtelomeric deletions of 1 Mb in size were excluded for 27 of 40 chromosome arms. Among the 120 subjects none was found to have UPD, but five subjects (4%, 95% confidence interval 1-9%) were found to have a deletion or duplication of one or more chromosome arms. We conclude that UPD is not a frequent cause of undiagnosed multiple congenital anomaly syndrome. In addition, we determined that 9p and 7q harbor chromosome length variations in the normal population. We conclude that subtelomeric marker analysis is effective for the detection of subtelomeric duplications and deletions, although it is labor intensive. Given a detection rate that is similar to prior studies and the large workload imposed by STRPs, we conclude that STRPs are an effective, but impractical, approach to the determination of segmental aneusomy given current technology.

Severe lactic acidosis caused by a novel frame-shift mutation in mitochondrial-encoded cytochrome c oxidase subunit II.

We report the first frame-shift truncation mutation in a mitochondrial DNA (mtDNA)-encoded subunit II of cytochrome c oxidase (COXII). The mutation was identified by temporal temperature gradient gel electrophoresis (TTGE) followed by direct DNA sequencing in an infant who died at 12 days of age following a course of apnea, bradycardia, and severe lactic acidosis. The patient had a twin brother who died at two days of age of similar course. The mutation, 8042delAT, produced a truncated protein that was 72 amino acids shorter than the wild type protein. The mutant protein, missing one third of the amino acid residues at the C-terminal essential for hydrophilic interaction with cytochrome c, ligand binding to CuA and Mg, and the formation of proton and water channels, apparently has devastating effects on mitochondrial respiratory function.

OA1 mutations and deletions in X-linked ocular albinism.

X-linked ocular albinism (OA1), Nettleship-Falls type, is characterized by decreased ocular pigmentation, foveal hypoplasia, nystagmus, photodysphoria, and reduced visual acuity. Affected males usually demonstrate melanin macroglobules on skin biopsy. We now report results of deletion and mutation screening of the full-length OA1 gene in 29 unrelated North American and Australian X-linked ocular albinism (OA) probands, including five with additional, nonocular phenotypic abnormalities (Schnur et al. 1994). We detected 13 intragenic gene deletions, including 3 of exon 1, 2 of exon 2, 2 of exon 4, and 6 others, which span exons 2-8. Eight new missense mutations were identified, which cluster within exons 1, 2, 3, and 6 in conserved and/or putative transmembrane domains of the protein. There was also a splice acceptor-site mutation, a nonsense mutation, a single base deletion, and a previously reported 17-bp exon 1 deletion. All patients with nonocular phenotypic abnormalities had detectable mutations. In summary, 26 (approximately 90%) of 29 probands had detectable alterations of OA1, thus confirming that OA1 is the major locus for X-linked OA.

Genetic heterogeneity of Saethre-Chotzen syndrome, due to TWIST and FGFR mutations.

Thirty-two unrelated patients with features of Saethre-Chotzen syndrome, a common autosomal dominant condition of craniosynostosis and limb anomalies, were screened for mutations in TWIST, FGFR2, and FGFR3. Nine novel and three recurrent TWIST mutations were found in 12 families. Seven families were found to have the FGFR3 P250R mutation, and one individual was found to have an FGFR2 VV269-270 deletion. To date, our detection rate for TWIST or FGFR mutations is 68% in our Saethre-Chotzen syndrome patients, including our five patients elsewhere reported with TWIST mutations. More than 35 different TWIST mutations are now known in the literature. The most common phenotypic features, present in more than a third of our patients with TWIST mutations, are coronal synostosis, brachycephaly, low frontal hairline, facial asymmetry, ptosis, hypertelorism, broad great toes, and clinodactyly. Significant intra- and interfamilial phenotypic variability is present for either TWIST mutations or FGFR mutations. The overlap in clinical features and the presence, in the same genes, of mutations for more than one craniosynostotic condition-such as Saethre-Chotzen, Crouzon, and Pfeiffer syndromes-support the hypothesis that TWIST and FGFRs are components of the same molecular pathway involved in the modulation of craniofacial and limb development in humans.

Brachydactyly-short stature-hypertension (Bilginturan) syndrome: report on two families.

We report on two families with autosomal dominant brachydactyly of hands and feet and hypertension. All affected members of the first family had proportionate short stature. However, the propositus and the affected relatives in the second family were only short compared to unaffected relatives. The hypertension was medically responsive in all cases. The propositus in the second family had poor compliance and a striking generalized vasculopathy. All patients were of normal intelligence and had a normal facial appearance. The brachydactyly-short stature-hypertension syndrome was first reported by Bilginturan et al. [1973] in a Turkish family and the families reported by us are Caucasian and Hispanic. The gene causing this condition in the original Turkish family was recently mapped to 12p. Our report expands our existing knowledge and the ethnic diversity of this syndrome.

Phenotypic variability in X-linked ocular albinism: relationship to linkage genotypes.

One hundred nineteen individuals from 11 families with X-linked ocular albinism (OA1) were studied with respect to both their clinical phenotypes and their linkage genotypes. In a four-generation Australian family, two affected males and an obligatory carrier lacked cutaneous melanin macroglobules (MMGs); ocular features were identical to those of Nettleship-Falls OA1. Four other families had more unusual phenotypic features in addition to OA1. All OA1 families were genotyped at DXS16, DXS85, DXS143, STS, and DXS452 and for a CA-repeat polymorphism at the Kallmann syndrome locus (KAL). Separate two-point linkage analyses were performed for the following: group A, six families with biopsy-proved MMGs in at least one affected male; group B, four families whose biopsy status was not known; and group C, OA-9 only (16 samples), the family without MMGs. At the set of loci closest to OA1, there is no clear evidence in our data set for locus heterogeneity between groups A and C or among the four other families with complex phenotypes. Combined multipoint analysis (LINKMAP) in the 11 families and analysis of individual recombination events confirms that the major locus for OA1 resides within the DXS85-DXS143 interval. We suggest that more detailed clinical evaluations of OA1 individuals and families should be performed for future correlation with specific mutations in candidate OA1 genes.

A de novo 13 nt deletion, a newly identified C647W missense mutation and a deletion of exon 18 in infantile onset glycogen storage disease type II (GSDII).

We identified the presumably rare event of de novo mutation in an autosomal recessive disorder, glycogen storage disease type II (GSDII). GSDII results from inherited deficiency of acid alpha-glucosidase (acid maltase) and both the expressed and structural gene (designated GAA) have been isolated. The mutation was a deletion of 13 nt of coding sequence (delta nt 1456-1468) on the paternally derived allele of the proband. The delta nt 1456-1468 results in a reading frameshift and a premature termination signal upstream of the enzyme catalytic site. Paternity was confirmed by presence of two downstream, uncommon amino acid substitutions (E689K, W746C) in both proband and father and by comparison of nine short tandem repeats. The maternal allele carried a newly identified deleterious C647W missense mutation in a highly conserved area of the protein. The C647W mutation was also found in a second unrelated proband, heteroallelic with a deletion extending from IVS17 to IVS18.

Focal dermal hypoplasia: four cases with widely varying presentations.

We describe four patients with focal dermal hypoplasia (FDH): a girl with classic FDH, a boy with cutaneous findings, an infant with severe multisystem disease, and the infant's mother, who had previously undiagnosed FDH. These patients illustrate the classic cutaneous manifestations of FDH and the variations that can exist within a family.

Pleiotropy in Coffin-Lowry syndrome: sensorineural hearing deficit and premature tooth loss as early manifestations.

We report on 7 patients (6 M, 1 F) with Coffin-Lowry syndrome who have a sensorineural hearing deficit in addition to developmental delay and characteristic facial changes. One of the patients also had a history of premature exfoliation of primary teeth. These are previously unappreciated clinical signs that may aid in the early diagnosis of Coffin-Lowry syndrome. Early diagnosis and recognition of a hearing deficit in the patient can lead to the use of hearing aids to help the patient achieve his or her full potential. These "new" clinical manifestations expand the phenotype of Coffin-Lowry syndrome and constitute an additional indication of pleiotropy.

Interstitial deletion of the short arm of chromosome 1 (46XY, del(1)(p13p22.3))

A male patient with a de novo proximal interstitial deletion of the short arm of chromosome 1 (46XY, del(1)(p13p22.3) is described with multiple anomalies and developmental delay. This patient's clinical manifestations are compared to previously reported patients with deletions of chromosome 1p.

Dyskeratosis congenita associated with elevated fetal hemoglobin, X-linked ocular albinism, and juvenile-onset diabetes mellitus.

An 11-year-old boy had dyskeratosis congenita, elevated fetal hemoglobin level, X-linked ocular albinism, and juvenile-onset diabetes mellitus. A review of the international literature revealed that elevated fetal hemoglobin has been noted in 15 reported cases of dyskeratosis congenita. It is a previously unrecognized, commonly associated finding in dyskeratosis congenita that may provide insight into the location and function of the gene for dyskeratosis congenita.

Absence of malignant hyperthermia contractures in Becker-Duchenne dystrophy at age 2.

Two 2-year-old males underwent muscle biopsy that established the histopathologic diagnosis of Becker dystrophy in one, and Duchenne dystrophy in the other. Concomitant contracture testing with caffeine or halothane was normal for malignant hyperthermia (MH). The results suggest that acute hypermetabolism or acute rhabdomyolysis during anesthesia, in patients with these disorders, is related to the X-linked myopathy and its associated muscle deterioration, rather than to the autosomal dominant MH.

Intermediate hyperhomocysteinemia resulting from compound heterozygosity of methylenetetrahydrofolate reductase mutations.

Four subjects with thermolabile methylenetetrahydrofolate reductase (MTHFR) were discovered among 16 "obligate" heterozygotes for severe MTHFR deficiency and their family members. All four subjects had less than 25% of normal mean MTHFR specific activity in lymphocyte extracts. Three of them with normal serum folate and cyanocobalamin had intermediate hyperhomocysteinemia, and one with high serum folate and cyanocobalamin had no excessive accumulation of serum homocysteine. The biochemical features in these four subjects are distinguishable from subjects homozygous for the thermolabile MTHFR, whose specific activity is approximately 50% of the normal mean, and from heterozygotes for severe MTHFR deficiency, in whom the enzyme is thermostable and has a specific activity of about 50% of the normal mean. We propose that these four subjects are genetic compounds of the allele for the severe mutation and the allele for thermolabile mutation of the MTHFR gene. It is postulated that subjects with this genetic compound are more susceptible to the development of intermediate hyperhomocysteinemia despite normal folate and B12 levels. Nonetheless, hyperhomocysteinemia due to this compound heterozygosity is correctable by oral folic acid therapy.

Diagnostic criteria for Walker-Warburg syndrome.

Walker-Warburg syndrome (WWS) is an autosomal recessive disorder manifest by characteristic brain and eye malformations. We reviewed data on 21 of our patients and an additional 42 patients from the literature. From this review, we expand the phenotype to include congenital muscular dystrophy (CMD) and cleft lip and/or palate (CLP), and revise the diagnostic criteria. Four abnormalities were present in all patients checked for these anomalies: type II lissencephaly (21/21), cerebellar malformation (20/20), retinal malformation (18/18), and CMD (14/14). We propose that these comprise necessary and sufficient diagnostic criteria for WWS. Two other frequently observed abnormalities, ventricular dilatation with or without hydrocephalus (20/21) and anterior chamber malformation (16/21), are helpful but not necessary diagnostic criteria because they were not constant. All other abnormalities occurred less frequently. Congenital macrocephaly with hydrocephalus (11/19) was more common than congenital microcephaly (3/19). Dandy-Walker malformation (10/19) was sometimes associated with posterior cephalocele (5/21). Additional abnormalities included slit-like ventricles (1/21), microphthalmia (8/21), ocular colobomas (3/15), congenital cataracts (7/20), genital anomalies in males (5/8), and CLP (4/21). Median survival in our series was 9 months. A related autosomal recessive disorder, Fukuyama congenital muscular dystrophy, consists of similar but less severe brain changes and CMD. It differs from WWS because of consistently less frequent and severe cerebellar and retinal abnormalities. We think that WWS is identical to "cerebro-oculo-muscular syndrome" and "muscle, eye, and brain disease."

Dyssegmental dysplasias: clinical, radiographic, and morphologic evidence of heterogeneity.

The dyssegmental dysplasias are lethal forms of neonatal short-limbed dwarfism in which vertebral segmentation defects and short, thick, bowed long bones are the prominent radiographic features. Clinically, unusual facies, short neck, narrow thorax, cleft palate, and reduced joint mobility are commonly seen. To date, 18 cases of dyssegmental dysplasia have been reported. Reports of three pairs of affected sibs suggest autosomal recessive inheritance. We have studied eight additional cases of dyssegmental dysplasia, including one pair of affected sibs. Clinical, radiographic, and histologic examination of these new cases and review of the literature demonstrates the presence of at least two distinct forms of dyssegmental dysplasia. The milder form, "dyssegmental dysplasia, type Rolland-Desbuquois," is characterized clinically by frequent survival beyond the newborn period and by distinct radiographic changes resembling Kniest dysplasia. The severe form, "dyssegmental dysplasia, type Silverman-Handmarker," is characterized by stillbirth or death within the first few days of life and by distinct and more severe radiographic changes. In addition, we have demonstrated chondro-osseous morphologic differences between the two disorders by light and electron microscopy. We conclude that there are at least two forms of dyssegmental dysplasia, each autosomal recessive, which can be delineated on clinical, radiographic and morphologic grounds.