Interstitial deletion for a region in the long arm of chromosome 16

Deletion of 16q22.2q23.3 in a Boy with a Phenotype Reminiscent of Silver-Russell Syndrome

A 15-month-old boy presented with growth and global developmental delay, feeding difficulties, sleep disturbance and several minor anomalies, including a large anterior fontanel, relative macrocephaly, and a triangular face. Clinical suspicion prompted genetic investigations for Silver-Russell syndrome and related disorders. SNP array analysis led to the diagnosis of an approximately 10-Mb large deletion of the long arm in chromosome 16q22.2q23.3. Interstitial deletions of 16q show a wide variability of related features; however, considering the differences in size and location of the deletions in the known patients, the phenotypic overlap is surprising. Here, we report a novel microdeletion, compare the proband with data from scientific literature and international databases, and discuss possible diagnostic implications.

Identification and characterization of novel ACD variants: modulation of TPP1 protein level offsets the impact of germline loss-of-function variants on telomere length

Telomere biology disorders, largely characterized by telomere lengths below the first centile for age, are caused by variants in genes associated with telomere replication, structure, or function. One of these genes, ACD, which encodes the shelterin protein TPP1, is associated with both autosomal dominantly and autosomal recessively inherited telomere biology disorders. TPP1 recruits telomerase to telomeres and stimulates telomerase processivity. Several studies probing the effect of various synthetic or patient-derived variants have mapped specific residues and regions of TPP1 that are important for interaction with TERT, the catalytic component of telomerase. However, these studies have come to differing conclusions regarding ACD haploinsufficiency. Here, we report a proband with compound heterozygous novel variants in ACD (NM_001082486.1)-c.505_507delGAG, p.(Glu169del); and c.619delG, p.(Asp207Thrfs*22)-and a second proband with a heterozygous chromosomal deletion encompassing ACD: arr[hg19] 16q22.1(67,628,846-67,813,408)x1. Clinical data, including symptoms and telomere length within the pedigrees, suggested that loss of one ACD allele was insufficient to induce telomere shortening or confer clinical features. Further analyses of lymphoblastoid cell lines showed decreased nascent ACD RNA and steady-state mRNA, but normal TPP1 protein levels, in cells containing heterozygous ACD c.619delG, p.(Asp207Thrfs*22), or the ACD-encompassing chromosomal deletion compared to controls. Based on our results, we conclude that cells are able to compensate for loss of one ACD allele by activating a mechanism to maintain TPP1 protein levels, thus maintaining normal telomere length.

Identification of a submicroscopic 3.2 Mb chromosomal 16q12.2-13 deletion in a child with short stature, mild developmental delay, and craniofacial anomalies, by high-density oligonucleotide array-a recognizable syndrome

Interstitial deletion of 16q has emerged into a recognizable pattern of congenital malformation. We report on a 9-year-old boy with short stature, psychomotor retardation, high forehead, broad flat nasal bridge, hypertelorism, cup-shaped ears, short neck, and a normal karyotype. Using high-density oligonucleotide array chip (Affymetrix 6.0) to perform parental and proband samples concurrently on three chips and interpreted as a trio set, a de novo 3.2 Mb deletion from bands q12.2 to q13 on chromosome 16 (from 52.08 to 55.3 Mb) of paternal origin was identified. The deletion was confirmed by quantitative genomic PCR and the break points were defined by junction PCR. Our study demonstrated the power of high-density oligonucleotide array chip in identifying novel submicroscopic deletions that were not detectable using G-banding cytogenetic technology. Furthermore, our result narrowed down the critical region for craniofacial features in interstitial 16q11.2-q13 deletion syndrome. In patients who have high forehead, broad flat nasal bridge, hypertelorism, cup-shaped ears, short neck and short stature, high-density array should be included in initial work up.

Tetralogy of Fallot associated with pulmonary atresia and major aortopulmonary collateral arteries in a patient with interstitial deletion of 16q21-q22.1

A newborn male had an interstitial deletion of 16q21-q22.1 accompanying tetralogy of Fallot associated with pulmonary atresia and major aortopulmonary collateral arteries (MAPCA), dysmorphic craniofacial features, failure to thrive, and severe psychomotor developmental delay. When the deletion in this patient and other reported patients are compared, the 16q22 region appears to be the smallest region for 16q deletion syndrome. Since over 50% of patients with the deletion of 16q22 region have congenital heart disease, there may be a responsible gene in this region.

Dominant inheritance of cleft palate, microstomia and micrognathia--possible linkage to the fragile site at 16q22 (FRA16B)

We report a family in which a father and his three children are affected with microstomia, micrognathia and partial or complete cleft of the hard and soft palate. The probands were non-identical twins, a boy and a girl, both noted to have the above features soon after birth. Their father was diagnosed with a submucous cleft of the palate at the age of 4 years and their older brother has milder facial features and a bifid uvula. All affected family members were demonstrated to have a fragile site on chromosome 16q22 but otherwise normal karyotypes. Of interest is a previously described family with autosomal dominant inheritance of U-shaped cleft palate, microstomia, micrognathia and oligodontia where all affected members were shown to have the fragile site at 16q22 in a proportion of their cells [Bettex et al. (1998) Eur J Pediatr Surg 8:4-8]. We propose that these two conditions are the same and represent a distinctive syndrome involving aberrant orofacial development that may be linked to the fragile site at 16q22.

Cytogenetic and clinical findings in a patient with a deletion of 16q23.1: first report of bilateral cataracts and a 16q deletion

The most commonly reported manifestations of 16q deletions are severe growth and developmental disorders and anomalies of the craniofacial, visceral, and musculoskeletal systems. We reviewed the findings of patients reported with 16q- syndrome and compared them to our patient, a 4 1/2-year-old boy with a deletion of 16q23.1. Findings include psychomotor retardation, hypotonia, high forehead, hypertelorism, upslanting palpebral fissures, low-set abnormally modeled ears, and talipes equinovarus. Anomalies present in our patient not reported in others with 16q- syndrome include bilateral cataracts, iris coloboma, and autistic-like behavior. It is of note that a locus for autosomal dominant congenital cataract, known as Marner cataract, was mapped previously to 16q22. Because our patient has bilateral cataracts and a unilateral iris coloboma, it seems likely that a gene involved in ocular development is located within 16q23.1. Our patient's deletion may also include the gene involved in Marner cataract and may further assist in the isolation of this gene.

High resolution mapping of interstitial long arm deletions of chromosome 16: relationship to phenotype

The breakpoints of seven interstitial deletions of the long arm of chromosome 16 and two ring chromosomes of this chromosome were mapped by in situ hybridisation or by analysis of mouse/human somatic cell hybrids containing the deleted chromosome 16. Use of a high resolution cytogenetic based physical map of chromosome 16 enabled breakpoints to be assigned to an average resolution of at least 1.6 Mb. In general, interstitial deletions involving q12 or q22.1 have broadly similar phenotypes though there are differences in specific abnormalities. Deletions involving regions more distal, from 16q22.1 to 16q24.1, were associated with relatively mild dysmorphism. One region of the long arm, q24.2 to q24.3, was not involved in any deletion, either in this study or in any previous report. Presumably, monosomy for this region is lethal. In contrast, patients with deletions of 16q21 have a normal phenotype. These results are consistent with the proposed distribution of genes, frequent in telomeric Giesma light band regions but infrequent in G positive bands.

De novo interstitial deletion 16(q12.1q13) of paternal origin in a 10-year-old boy

A 10-year-old boy with a de novo del(16)(q12.1q13) and many features of the deletion 16q phenotype is described. The deletion occurred in a paternal chromosome as demonstrated by DNA studies with polymorphic (AC)n microsatellite repeat markers. Comparison with published cases suggests that deletion of either of two regions (q13 and q22.1) on the long arm of chromosome 16 is associated with an apparently identical phenotype. No parental imprinting of this region was demonstrated.

Interstitial deletion of chromosome 16q: 16q22 is critical for 16q- syndrome

Partial deletion of 16q is rare; to our knowledge only 12 cases have been published. Fryns et al. [Hum Genet 38:343-346, 1977] described the first of these cases and proposed a new clinical entity. Our patient was a girl and had many minor anomalies of the kind often observed in 16q- syndrome. Severe failure to thrive due to emesis and diarrhea were also observed. High resolution banding methods showed that the chromosome constitution of the patient was 46,XX,del(16)(q22.1q22.3). This suggests that 16q22 is critical for the syndrome.

Nonrandom association of atrioventricular canal and del (8p) syndrome

We describe a patient with partial deletion of the short arm of chromosome 8 with an atrioventricular canal. This type of congenital heart defect was found in 4 of the 7 previously reported del (8p) children with a congenital heart defect in which the cardiac assessment was complete. The prevalence of an atrioventricular canal in this aneuploidy is high and suggests a nonrandom association of the 2 anomalies.

Deletion of 16q with prolonged survival and unusual radiographic manifestations

Deletion of 16q is characterized by mental retardation, microcephaly, a characteristic combination of minor facial anomalies, and broad halluces. Various break points have been described. This patient's phenotype is typical of this syndrome, but in addition, unusual radiographic findings were present. This chromosome abnormality is compatible with survival into adulthood. Expression of this phenotype does not appear to be correlated with specific break points.

Re-evaluation of GM2346 from a del(16)(q22) to t(4;16)(q35;q22.1)

Reassessment of the cytogenetics of a patient previously karyotyped as del(16)(q22) demonstrates the presence of a balanced translocation, t(4;16)(q35;q22.1). This patient should not be included in any future comparison involving the clinical features of patients with deletions of the long arm of chromosome 16.

16q21 is critical for 16q deletion syndrome

A 1-year-old girl with an interstitial deletion of the long arm of chromosome 16 is reported. She was characterized by a distinct craniofacial dysmorphism, meningoencephalocele, mild hydrocephalus, short neck, broad great toes and abnormally positioned toes. High resolution GTG and RBG banding analyses revealed a karyotype: 46,XX,del(16) (q13q22) de novo. An analysis of the smallest region of overlap revealed that the critical band region for 16q deletion syndrome is 16q21.

Inherited and de novo deletion of the tyrosine aminotransferase gene locus at 16q22.1----q22.3 in a patient with tyrosinemia type II

Tyrosinemia II is an autosomal-recessively inherited condition caused by deficiency in the liver-specific enzyme tyrosine aminotransferase (TAT; EC 2.6.1.5). We have restudied a patient with typical symptoms of tyrosinemia II who in addition suffers from multiple congenital anomalies including severe mental retardation. Southern blot analysis using a human TAT cDNA probe revealed a complete deletion of both TAT alleles in the patient. Molecular and cytogenetic analysis of the patient and his family showed one deletion to be maternally inherited, extending over at least 27 kb and including the complete TAT structural gene, whereas loss of the second TAT allele results from a small de novo interstitial deletion, del 16 (pter----q22.1::q22.3----qter), in the paternally inherited chromosome 16. Three additional loci previously assigned to 16q22 were studied in our patient: haptoglobin (HP), lecithin: cholesterol acyltransferase (LCAT), and the metallothionein gene cluster MT1,MT2. Of these three markers, only the HP locus was found to be codeleted with the TAT locus on the del(16) chromosome.

Interstitial deletion and ring chromosome derived from 16q

An interstitial deletion of 16q was identified in an infant with failure to thrive, dysmorphic facies, and congenital heart defects. The mother of this infant had a similar deletion of 16q with ring formation of a fragment presumed to be derived from the deleted portion of 16q. We discuss these cases and compare them to other reports of 16q deletions.

Multiple congenital anomalies syndrome with myopathy in chromosome 16 abnormality

An abnormality of chromosome 16 in an eight year-old male was associated with a multiple congenital anomalies syndrome characterized by myopathy, cataracts, blepharophimosis, microcephaly, failure to grow, profound mental retardation, moderate sensorineural hearing loss, grand mal seizures, bilateral inguinal hernia, and thoracolumbar kyphoscoliosis. Magnetic resonance imaging of the head demonstrated absence of the corpus callosum and extensive loss of brain parenchyma in the occipital regions. Chromosome analysis from peripheral blood of the patient showed a recombinant chromosome 16 [46, XY, rec (16), dup (p13.1----p13.3) del (q22----q24)]. The mother had a pericentric inversion of chromosome 16 [46, XX, inv(16) (p13.1;q22)]. Independent recombinant DNA studies have shown that the breakpoints of these chromosomal rearrangements flank the alpha-globin gene cluster locus.

Familial fragile site found at the cancer breakpoint (1)(q32). Inducibility by distamycin A, concomitance with fragile (16)(q22)

A normal baby was cytogenetically examined immediately after birth for the possible presence of a fragile (16)(q22), which had been found in her mother and in her retarded sister with a 46,XX;46,XX,del(16)(q22) mosaic karyotype. Distamycin A was added to the cultures to enhance the fragile (16)(q22) expression. The response of the baby to the action of distamycin A in vitro was much greater than that of her family members. A fragile (16)(q22) was induced in many cells as well as a fragile (1)(q32), which was also found in her mother. This fragile site, which is known to be a cancer breakpoint, has not been reported so far either to be familial or to be inducible by distamycin A. The concomitance of fragile (1)(q32) with fragile (16)(q22) and their possible significance are considered.

Monosomy 16q: a distinct syndrome. Apropos of a de novo del(16) (q2100q2300)

A 2-month-old boy with delayed growth and development, brachycephaly, large anterior fontanelle, low-set folded ears, micrognathia, aortic coarctation, floppy abdominal muscles, and pes varus, was found to have a 46,XY,del(16)(q2100q2300) de novo karyotype. This observation corroborates both the distinctness of the 16q monosomy syndrome and the pathogenetic role of the band 16q21.

Recurrent de novo interstitial deletion of 16q in two mentally retarded sisters

Two sisters with similar clinical features are described. Their clinical manifestations include mental retardation, delayed speech development, low percentiles for height, weight and head circumference, dysmorphic ears, cubitus valgus, pseudoclubbing of fingers, flexion deformity of toes, small kidneys, elevated serum creatinine and blood urea nitrogen (BUN). High resolution chromosome analysis revealed a complete deletion of 16qh with a concurrent small deletion of the adjacent euchromatic segment 16q12.1 in one of the no. 16 chromosomes of both sisters, whereas the parents had normal no. 16 chromosomes. Length polymorphism of the 16qh regions appeared to indicate a maternal origin of the deleted no. 16 chromosome in both sisters. The clinical features of both sisters were attributed to the 16q12.1 deletion. Since both parents were cytogenetically normal, the two sisters were considered as a recurrence of a similar de novo interstitial deletion. Possible mechanisms which could lead to recurrence of a seemingly de novo event are discussed.

Identical twins with deletion 16q syndrome: Evidence that 16q12.2-q13 is the critical band region

An interstitial deletion of the long arm of chromosome 16 has been identified in identical twins. These patients are strikingly similar phenotypically to previously reported cases of deletion 16q syndrome but differ chromosomally in that their deletion involves the 16q12.2-q13 rather than the 16q21. We propose that the 16q12.2-q13 is the "critical region" in the production of this rare but distinctive phenotype.