Malan syndrome ( Sotos syndrome 2 ) in two patients with 19 p 13 . 2 deletion encompassing NFIX gene and novel NFIX sequence variant

Background and Aim. Sotos syndrome 2 (MIM #614753), known also as Malan syndrome, is caused by heterozygous mutations/deletions of the NFIX gene located on chromosome 19p13.2. It manifests in developmental delay, intellectual impairment, macrocephaly, central nervous system anomalies, postnatal overgrowth, and craniofacial dysmorphism. Unusual behavior with/without autistic traits, ophthalmologic, gastrointestinal, musculo-skeletal, and hand/foot abnormalities are also frequent. Due to the limited number of such cases, no definitive conclusions about genotypephenotype correlations have been possible. In the following paper, we discuss physical features consistent with Sotos syndrome 2 based on literature review and two new cases [a patient with de novo 19p13.2 deletion encompassing a part of the NFIX gene and a patient with de novo (not described so far) heterozygous missense mutation c.367C>T (p.Arg123Trp) in the NFIX gene]. Results. Apart from overgrowth and psychomotor developmental delay, the most consistent physical features of our two patients are dysmorphism including high forehead, downslanting palpebral fissures, pointed chin, and abnormalities of the pinna. Both show abnormal behavior and present with long, tapered fingers and toenail defect. No severe congenital malformations were noted. Conclusions. We hope these data will serve as a material for further studies and provide an opportunity to make more reliable genotype-phenotype correlations.


INTRODUCTION
Aberrations in 19p13.2(or 19p13.13according to the hg18) result in diverse clinical phenotypes depending on the size of the affected fragment and involved genes (in large deletions/duplications) as well as type of point mutations.Descriptions of patients presented so far in the literature comprise several cases of chromosomal aberrations in 19p13.2/19p13.13band reported by Lysy et al. 1 , Dolan et al. 2 , Malan et al. 3 , Bassuk et al. 4 , Wangensteen et al. 5 , Natiq et al. 6 , Schwemmle et al. 7 , Klaassens et al. 8 , Shimojima et al. 9 and point mutations in NFIX gene (localized within 19p13.2) reported by Malan et al. 3 , Klaassens et al. 8 , Priolo et al. 10 , Yoneda et al. 11 in patients with Sotos-like and Marshall-Smith (MRSHSS) syndromes.Unfortunately, due to the limited number of these cases, no definitive conclusions about the genotype-phenotype correlations can be made.
As patients with 19p13.2 and NFIX gene aberrations have been described in previous papers 2,3,6,8,10 , we will not present another detailed comparison.Instead our goal is to discuss physical features consistent with Sotos syndrome 2 (Malan syndrome) based on literature review and two new cases.We hope these data will serve as a material for further studies, involving larger group of patients, and hence will provide an opportunity to make more reliable genotype-phenotype correlations.

MATERIAL AND METHODS
After obtaining informed consent, the genomic DNA was extracted from probands' and their parents' peripheral blood samples using the automatic method (MagnaPure, Roche).
High-resolution chromosomal analyses were performed using the whole-genome oligonucleotide microarrays, i.e., PerkinElmer CGX™ HD v1.1 v1.1 4-plex (180 K array; hg19) and NimbleGen CGX-3 v1.0 3-plex (720 K array; hg18).Digestion, ligation, PCR, labeling, and hybridization of test and reference DNA were performed according to the manufacturer's recommendations.The slides were scanned into image files using the MS 200 Microarray Scanner (NimbleGen).Feature extraction and primary data analysis were performed using Agilent CytoGenomics Edition 2.7.22.0 software or NimbleGen DEVA software (depending on the type of microarray).Signature Genomics' Genoglyphix genome browser software was used for detailed analysis and data visualization.
NGS (next-generation sequencing) analysis was performed using TruSightOne Sequencing Panel (Illumina) according to the manufacturer's instructions.The samples were run on 1/12 of lane each on HiSeq 1500 using 2x75 bp paired-end reads.Bioinformatics analysis was performed as previously described 12 .Briefly, after initial processing by the CASAVA, the generated reads were aligned to the hg19 reference genome with Burrows-Wheeler Alignment Tool 13 and further processed by Genome Analysis Toolkit 14 .Base quality score recalibration, indel realignment, duplicate removal and the SNP/ INDEL calling were done as described 15 .The detected variants were annotated using Annovar 16 and converted to MS Access format for final manual analyses.In the analyzed probe 76.6% of target was covered minimum 20 times.Alignments were viewed with Integrative Genomics Viewer v.2.3.40 (ref. 17).

PATIENT NM (DELETION OF 19p13.2)
The girl was referred for genetic counseling because of psychomotor delay.Her family history is unremarkable.She is a first child born at 40 weeks gestation after a pregnancy complicated by preterm contractions, by caesarean section (because of breech position) with 10 points in the Apgar scale, a weight of 3020 g (15th-50th centile), length of 56 cm (>97th centile) and occipitofrontal circumference (OFC) of 36 cm (85th-97th centile) (Table 1).
During further development, delay in language and motor skills as well as poor coordination were noted.She presents poor wound healing, bruising susceptibility, accelerated skeletal maturation (+2.5 years), dental malocclusion, strabismus, and constipation.The craniofacial examination revealed: triangular face with high forehead, hypertelorism, short and downslanting palpebral fissures, smooth philtrum, abnormality of the pinna, narrow mouth with open-mouth appearance, and pointed chin (Fig. 1).Moreover, long and tapered fingers, aplasia/hypoplasia of the palmar creases, clinodactyly of the 4th finger as well as overlapping toe and abnormality of the toenails were observed (all features are listed in Table 2).
She also presents behavioral anomalies (anxiety, tantrums, autoaggression), but in general, she is rather a cheerful child.Even though she can speak only a few words (mummy, daddy), she understands much more and executes commands.She also has a preference for waterrelated items.The previous genetic diagnostics testing: GTG-banding karyotyping, MLPA (Multiplex Ligation-dependent Probe Amplification) for subtelomeric regions (SALSA MLPA P036 and P070 kits; MRC-Holland), MLPA for MECP2, CDKL5, ARX, NTNG1 genes (SALSA MLPA P015 kit) and MS-MLPA toward Angelman syndrome (SALSA MS-MLPA ME028 kit) gave normal results.

PATIENT AB (NFIX MUTATION)
The girl was diagnosed because of psychomotor delay.Her family history is unremarkable.She was born after infertility treatment (with intrauterine insemination) at 40 weeks gestation, after an uneventful pregnancy with 10 points in the Apgar scale, a weight of 3350 g (50th-75th centile), length of 56 cm (>97th centile) and OFC of 33 cm (15th-50th centile) (Table 3).
During further development, delay in language and motor skills, muscular hypotonia, broad-based gait with poor coordination, and generalized joint laxity were noted.The craniofacial examination revealed: long face with    high and broad forehead, downslanting palpebral fissures, short columella and short philtrum, thin vermillion border, abnormality of the pinna, and pointed chin (Fig. 4).Moreover, long, tapered fingers and abnormality of the toenails were observed.She presents behavioral abnormal-at least two of the following features: 1. advanced bone age, 2. dysmorphic craniofacial features, 3. congenital malformations led to identification of first two cases with 19p13.1 monosomy 3 .Both patients had advanced bone age, long/narrow faces with high forehead, long fingers, slender habitus, and presented behavioral anomalies with autistic traits.Since the deleted region involved a single common gene, NFIX (Nuclear Factor I, X-type), it was considered to be a strong candidate in the cause of overgrowth in the investigated patients.Subsequently, these authors screened for NFIX mutations 76 patients with unexplained syndromic overgrowth, confirming a heterozygous de novo nonsense mutation in a patient previously diagnosed with Sotos-like syndrome 3 .Moreover, based on the observation of Nfixdeficient mouse model presenting a phenotype similar to Marshall-Smith syndrome, the group screened 9 patients with MRSHSS for NFIX mutations that allowed for the identification of 7 independent frameshift mutations and 2 different mutations within the donor splice site of exon 6.
Links between NFIX gene disturbances and phenotype resembling Sotos syndrome were also verified shortly after by Yoneda et al. who identified different heterozygous missense mutations in 2 patients negative for NSD1 mutation 11 .In 2012, Priolo et al. found in frame deletion of NFIX gene in a patient with overgrowth and suspected a mild form of Marshall-Smith syndrome (i.a.blue sclerae, mild proptosis, slightly bullet-shaped phalanges, and sleep apnea that spontaneously resolved with age) (ref. 10).As is now recognized, mutations in the DNA binding/dimerization domain of NFIX (leading to NFIX haploinsufficiency) are likely to cause Sotos-like syndrome, while Marshall-Smith syndrome is rather due to mutations with dominant negative effect [mutated RNAs escape nonsense-mediated decay (NMD)] (ref. 3,10,11).However, the NMD mechanism pertains exclusively to mutations leading to premature  ity with aggressive and self-injurious behavior.Myopia, strabismus, and EEG abnormalities were also diagnosed (all features are listed in Table 2).The previous genetic diagnostics testing which gave normal results included: GTG-banding karyotyping, FISH (fluorescence in situ hybridization) for 22q13, MLPA for subtelomeric regions (SALSA MLPA P036 and P070 kits) as well as for 5q35.3 region (SALSA MLPA P064 kit) and Cohen syndrome (SALSA MLPA P321 kit).
Finally, next-generation sequencing performed on HiSeq 1500 using TruSightOne Enrichment Kit revealed the presence of a molecular variant in the NFIX gene: a missense heterozygous substitution c.367C>T (p.Arg123Trp) in exon 2 (34/64 reads) which may be disease-causing (Fig. 5).At the same time, aberrations within coding sequences of NDS1 and VPS13B (COH1) genes were excluded.The identified alteration is a novel molecular variant not yet described in the genetic databases or literature.In order to evaluate the pathogenicity of the substitution bioinformatic analysis was performed.Novel variant acquired the status of diseasecausing change in seven predictive algorithms: CADD, RadialSVM, PolyPhen-2, LRT, LR, SIFT, and Mutation Taster.The variant in the patient was validated and the parental origin of this mutation was excluded by the Sanger sequencing.The nomenclature of mutation follows the guidelines of the Human Genome Variation Society (HGVS www.hgvs.org/mutnomen)using human NFIX-cDNA NM_001271043.2as a reference sequence followed the Human Gene Mutation Database (HGMD www.hgmd.cf.ac.uk).

DISCUSSION
In 2010, 244 K oligonucleotide arrays were performed by Malan et al. in 18 patients from non-consanguineous parents with developmental delay, height >95th centile and(or) occipitofrontal circumference >95th centile, and stop codons, and hence is not expected in our patient AB.As noted by Klaassens et al., variants found in the Marshall-Smith syndrome are frameshift and splice site within 6-8 exons 8 .In patient AB, the novel heterozygous missense mutation c.367C>T (p.Arg123Trp) in the DNAbinding/dimerization domain of NFIX was identified.Arginine 123 is a very highly conserved residue across species (Fig. 6).This substitution is predicted to be disease-causing.Thus it might be assumed that the missense mutation affects DNA-binding/dimerization domain of NFIX gene leading to its haploinsufficiency.
As was just recently proposed by Klaassens et al., who reviewed cases with Sotos-like overgrowth, a phenotype caused by whole gene deletions, nonsense variants and missense variants affecting the DNA-binding domain may be referred to as Malan syndrome 8 .Referring to these authors' results, we can support the data on the high frequency of strabismus among cases with Sotos syndrome 2, while none of described herein patients present with nystagmus or optic disc pallor/hypoplasia [noted in 25% of cases review by Klaassens et al. 8 ].In none of our patients pectus excavatum or scoliosis were observed, noted by cited authors as other recurrent features (respectively in 40% and 25% of cases).
As shown in Tables 1 and 3, birth weight was within normal limits in both our patients, and no overweight in postnatal period is observed.On the other hand, in both girls, birth length was above 97th centile, and constantly tends to be within 75th-90th centile.Patient NM (diagnosed with 19p13.2deletion) was born with larger OFC than patient AB (with point mutation in NFIX gene) -36 cm (85th-97th centile) vs. 33 cm (15th-50th centile), what may result from the fact that the deletion also includes other than NFIX genes.This measurement increased later in patient AB to 50th-75th at the age of 6.The postnatal onset in weight and OFC gain are noteworthy features of Malan syndrome, in contrast to Sotos syndrome (caused by mutation in the nuclear receptor binding SET domain protein 1, NSD1 gene), where the overgrowth is usually in prenatal period and is more significant.
Recognition of Malan syndrome on a clinical basis is however difficult.The differential diagnosis should take into account other overgrowth conditions that may be confused with the Sotos syndrome, such as: Weaver syndrome, Beckwith-Wiedemann syndrome, in males -Simpson-Golabi-Behmel syndrome as well as fragile X syndrome or benign familial macrocephaly in neurologically normal individuals.
Looking at Table 2, where clinical features described in patients with Sotos syndrome 2 are specified, it can be noted that, apart from overgrowth and psychomotor developmental delay, the most consistent physical features of our patients are dysmorphism including high forehead, downslanting palpebral fissures, pointed chin, and abnormalities of the pinna.Moreover, both present long, tapered fingers and abnormality of the toenails.No severe congenital malformations were noted.In general, they share a limited number of dysmorphic features.
On the contrary, they have a similar spectrum of motor abnormalities, such as poor coordination, which is known to be characteristic for patients with Sotos syndrome and NSD1 mutation.Likewise abnormal EEG was noted in both, however only patient with deletion 19p13.2suffers from seizures.Also both our probands show abnormal behavior, such as aggression, self-injurious behavior and -noted in patient NM -tantrums.In contrast to the observation of Malan et al. 3 , no autistic traits were observed in our patient with NFIX mutation.This is consistent with the observation of Yoneda et al. that missense mutations in the DNA-binding/dimerization domain do not lead to autistic traits 11 .Our patients show only some central nervous system anomalies -persistent cavum septum pellucidum and pineal cyst in patient NM and unilateral ventriculomegaly in patient AB.
When we compare the craniofacial appearance of our two probands, their gestalt is consistent with Sotos syndrome 2. However, it is quite clear that patient NM (diagnosed with 19p13.2deletion) has more pronounced dysmorphism, which, moreover, more closely corresponds to the facial characteristics found in Sotos syndrome 2 (regarding the ocular region, philtrum, and chin).
The clinical status of patient NM is probably influenced by the absence of other than NFIX genes located within the 19p13.2region -SYCE2, FARSA, CALR, RAD23A, GADD45GIP1, and DAND5.The DAND5 gene (*609068) encodes a member of the bone morphogenic protein antagonist family and may play a role in regulating organogenesis, body patterning, and tissue differentiation 18 .The CALR gene (*109091) encodes a chaperone protein mediating the attenuating effect of glucocorticoids in Wnt signalling in osteoblastic cells and thus plays an important role in controlling osteoblastogenesis 19 .It is also located in neurons in the human small intestine and therefore might play a role in the gastrointestinal issues 2 .The NFIX gene (*164005), which is known to be essential for normal brain development and is probably required for neural stem cell homeostasis, is also associated with the features observed in our presented patients 20 .As for the rest of mentioned genes, based on current data on their function we found no correlation to the phenotype of patient NM.
The de novo heterozygous missense mutation c.367C>T (p.Arg123Trp) in NFIX gene in patient AB affects highly conserved arginine and is suspected to be disease-causing by predictive algorithms.NFIX is a member of the nuclear factor I (NFI) family proteins implicated in site-specific DNA-binding proteins involved in viral DNA replication and gene expression regulation.Identified point mutation in the DNA-binding/dimerization domain of the NFIX protein might cause loss of dimerization, DNA-binding and replication activities but its exact role can only be verified in future studies.

CONCLUSIONS
This paper provides insight into the phenotype of Sotos syndrome 2, providing new clinical data important for distinguishing patients with NFIX mutations and deletions within 19p13.2 region.We hope that it will help in uncovering the molecular pathway leading to the Sotoslike phenotype and more precise diagnostics based on patients' clinical features.

Fig. 6 .
Fig. 6.Alignment of R123 amino acid in the NFIX protein showing conservation of the amino acid across species.

Table 2 .
Clinical features present in Sotos syndrome 2 described in the literature (symptoms observed in both our patients are marked in bold).

Table 3 .
Growth parameters of patient AB (with mutation in NFIX gene).