Mandibulofacial Dysostosis with Microcephaly: Mutation and Database Update

Mandibulofacial dysostosis with microcephaly (MFDM) is a multiple malformation syndrome comprising microcephaly, craniofacial anomalies, hearing loss, dysmorphic features, and, in some cases, esophageal atresia. Haploinsufficiency of a spliceosomal GTPase, U5-116 kDa/EFTUD2, is responsible. Here, we review the molecular basis of MFDM in the 69 individuals described to date, and report mutations in 38 new individuals, bringing the total number of reported individuals to 107 individuals from 94 kindreds. Pathogenic EFTUD2 variants comprise 76 distinct mutations and seven microdeletions. Among point mutations, missense substitutions are infrequent (14 out of 76; 18%) relative to stop-gain (29 out of 76; 38%), and splicing (33 out of 76; 43%) mutations. Where known, mutation origin was de novo in 48 out of 64 individuals (75%), dominantly inherited in 12 out of 64 (19%), and due to proven germline mosaicism in four out of 64 (6%). Highly penetrant clinical features include, microcephaly, first and second arch craniofacial malformations, and hearing loss; esophageal atresia is present in an estimated ∼27%. Microcephaly is virtually universal in childhood, with some adults exhibiting late "catch-up" growth and normocephaly at maturity. Occasionally reported anomalies, include vestibular and ossicular malformations, reduced mouth opening, atrophy of cerebral white matter, structural brain malformations, and epibulbar dermoid. All reported EFTUD2 mutations can be found in the EFTUD2 mutation database (http://databases.lovd.nl/shared/genes/EFTUD2).

Genotypic and phenotypic analysis of 396 individuals with mutations in Sonic Hedgehog

BACKGROUND

Holoprosencephaly (HPE), the most common malformation of the human forebrain, may result from mutations in over 12 genes. Sonic Hedgehog (SHH) was the first such gene discovered; mutations in SHH remain the most common cause of non-chromosomal HPE. The severity spectrum is wide, ranging from incompatibility with extrauterine life to isolated midline facial differences.

OBJECTIVE

To characterise genetic and clinical findings in individuals with SHH mutations.

METHODS

Through the National Institutes of Health and collaborating centres, DNA from approximately 2000 individuals with HPE spectrum disorders were analysed for SHH variations. Clinical details were examined and combined with published cases.

RESULTS

This study describes 396 individuals, representing 157 unrelated kindreds, with SHH mutations; 141 (36%) have not been previously reported. SHH mutations more commonly resulted in non-HPE (64%) than frank HPE (36%), and non-HPE was significantly more common in patients with SHH than in those with mutations in the other common HPE related genes (p<0.0001 compared to ZIC2 or SIX3). Individuals with truncating mutations were significantly more likely to have frank HPE than those with non-truncating mutations (49% vs 35%, respectively; p=0.012). While mutations were significantly more common in the N-terminus than in the C-terminus (including accounting for the relative size of the coding regions, p=0.00010), no specific genotype-phenotype correlations could be established regarding mutation location.

CONCLUSIONS

SHH mutations overall result in milder disease than mutations in other common HPE related genes. HPE is more frequent in individuals with truncating mutations, but clinical predictions at the individual level remain elusive.

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

Sorrell AD, Lee S, Stolle C, Ellenhorn J, Grix A, Kaelin Jr WG, Weitzel JN. 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 hydroxylation-dependent 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.

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.

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.

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.

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.

Alopecia-anosmia-deafness-hypogonadism syndrome revisited: report of a new case

Johnson et al [1983] reported on a large family with alopecia-anosmia-deafness-hypogonadism syndrome. We report the detailed findings of an unrelated, affected individual and emphasize the presence of hypohidrosis in our case. Our case indicates that this syndrome is not a private syndrome.

Direct prenatal chromosome diagnosis of a malignancy

A fetal tumor was suspected at 31 weeks of gestation. The occurrence of polyhydramnios led to an ultrasound examination, which revealed deformation of the fetal head, face, eye, and neck. This was confirmed by computerized tomography. Amniocentesis yielded cells with an inverted duplication of chromosome #1. This abnormality of chromosome #1 marked the malignant teratoma cells in the amniotic fluid. Cytogenetic analysis of tumor tissue and of normal tissue obtained postnatally confirmed that the abnormality of chromosome #1 observed in amniotic fluid cells was confined to the tumor. The constitutional karyotype was normal. To our knowledge, this is the first report of the direct chromosomal detection of malignancy before birth.