Phenotype and genotype in a Taiwanese girl with Sotos Syndrome

Rare copy number variations have been linked to an important source of mutation in many psychopathological traits and neurodevelopmental disorders. In this study, we describe a Taiwanese girl with mental retardation and mild macrocephaly who underwent a childhood psychological evaluation for several years first. When she was 5 years old, she came to our hospital for further diagnosis. We conducted molecular cytogenetic tests and confirmed she actually has Sotos syndrome. We compared our case with two others with very similar deletion regions, but their phenotypes were heterogeneous. Sotos syndrome is very rare in Taiwan, and it is suggested that genetic analysis should be considered early if symptoms of this case are observed.


Introduction
C opy number variations (CNVs) are polymorphisms in the number of copies of chromosomal microdeletions and microduplications (genomic rearrangements). They range from 1 kb to several Mb and have been reported to be causal suspects in various developmental disorders. CNVs may change the dosage balance of allele genes, generate new recombination of exons between different genes, or disrupt regulatory regions, resulting in variations in gene expression or altered protein structure and activity. Therefore, if CNVs are large and affect multiple genes, they are likely to be involved in different phenotypes, including disease sensitivity. CNVs can be inherited from a parent or arise de novo in an individual. Usually, de novo CNVs are more likely to have damaging effects [1].
Rare CNVs have been linked to an important source of mutation in many psychopathological traits and neurodevelopmental disorders, such as intellectual disability, autism spectrum disorders, attentiondeficit hyperactivity disorder, epilepsy, and schizophrenia [2]. Array comparative genomic hybridization (aCGH) is a high-resolution technology to detect rare CNVs on chromosomes that cannot be observed using conventional cytogenetic karyotyping [2]. Herein, we report on a 5-year-old Taiwanese girl with a phenotype of psychological developmental delay and mild macrocephaly with a high broad forehead and identified a de novo 1.86-Mb microdeletion at 5q35.2-q35.3 associated with Sotos syndrome.

Case and methods
The index patient was the first child of healthy non-consanguineous Taiwanese parents and was born by cesarean section at 38 weeks of gestational age following an uneventful pregnancy/delivery, except for amniotic fluid inhalation. The ages of the parents at conception were 32 (father) and 27 (mother) years. The birth weight was 3500 g (50e85th percentile), length of 53 cm (97th percentile), and head circumference was 38 cm (above the 97th percentile). Due to the large head circumference, electroencephalography and brain computerized tomography were performed shortly after birth and the results were unremarkable.
The parents reported that she started climbing at the age of 12 months and walked without support at 24 months. When she was 15 months old, she began receiving physical, language, and functional therapies. She was able to say "mama" and "papa" at 36 months and repeat the words overhead in conversation at the age of 5 years old. However, there has been no full sentence development yet. At the age of 34 months, the evaluation of psychomotor development according to the Bayley Scales of Infant and Toddler Development (BSID-III) was performed and showed that her cognition fell into the range of slow development (BSIDIII: CCI ¼ 65; 1 percentile), with a developmental age of approximately 17 months old; language skills fell under the scope of developmental delay (BSID-III: Lang ¼ 65; 1 percentile), with approximately 14 months of expression and 13 months of understanding.
The patient started kindergarten at 5 years of age. She could express her physical needs, such as going to the toilet and hunger using voice or simple words. She was easily attracted to things that interested her, such as mobile phones and e-books. Due to her lack of language ability, she often expressed herself as a means of pushing or beating other people. For the continuation of the psychotherapeutic interview and supportive psychotherapy, she was evaluated using the Adaptive Behavior Assessment System, Second Edition (ABAS-II) at 65 months of age. Her language and communication development was 16e26 months old, social and personality development was 21e40 months old, and perception and cognitive development were 11e29 months old. All these developmental parameters fell into the scope of developmental delay. The scores of the General Adaptive Composite were 70 (percentile rank [PR] ¼ 2; 95% CI ¼ 68e72), which fell within the critical range. The scores for the three subdomains were: 60 for conceptual (PR ¼ 0.4), 93 for social (PR ¼ 32), and 61 for practical (PR ¼ 0.5).
The patient was brought to the genetic outpatient clinic of our hospital at the age of 5 years (62 months) for genetic counseling regarding the psychological developmental delay. Her body height, weight and body mass index were 112.7 cm (50e85th percentile), 20.8 kg (85th percentile), and 16.3 kg/m 2 (50e85th percentile), respectively, according to the New Growth Charts for Taiwanese Children and Adolescents [3]. The Tanner stage was B1P1. On physical examination, she had a long face with a broad forehead, sparse eyebrows, mildly depressed nasal root, large ears, happy and friendly characteristics, above the mean stature, and macrocephaly (head circumference 57 cm, above the 97th percentile) [ Fig. 1A,B,C].

Results and discussion
According to Array-CGH result, we identified a 1.863 Mb deletion of 5q35.2e35.3 (arr[GRCh37](1-   Table 1]. This result is compatible with the diagnosis of Sotos syndrome. Sotos syndrome (OMIM 117550) is a disease characterized by overgrowth and intellectual disability with an incidence of approximately 1 in 15,000 live births [4]. Its inheritance pattern is autosomal dominant and is caused by a deletion or mutation in the NSD1 gene, which is mapped to 5q35.2-q35.3 [4,5]. The proportions of intragenic and microdeletion mutations in Sotos syndrome differ between countries. In East Asia, studies from Japan reported that 52% of Japanese patients with Sotos syndrome were microdeletions, but only 10e15% were observed in non-Japanese ethnicities [6,7]. In 2005, it was reported that in Hong Kong, Southern China, only 12% of Sotos syndrome cases were the microdeletion type, similar to that in a Western study [8]. In a study in Korea, 53% of Korean patients had 5q35 microdeletion [9]. In Taiwan, Sotos syndrome was very rare, and only one prenatal diagnosis case was reported; it was a girl with 5q35.2-q35.3 microdeletion but without follow-up information [10]. In this study, we describe the case of a patient with developmental delay who underwent a childhood mental evaluation for several years and confirmed the diagnosis of Sotos syndrome using molecular cytogenetic methods in the final.
Although Sotos syndrome cases are rare, we estimated that the microdeletion type of mutation should be dominant in Taiwanese Sotos syndrome.
The NSD1 gene encodes the nuclear receptor set domain protein 1, which is a histone methyltransferase that methylates lysine residues on histone tails [11]. Histones are structural proteins that bind to DNA, and methylation of histones is often associated with the transcription regulation of genes. NSD1 gene mutations disrupt the normal regulation of genes involved in cell/tissue growth and development [12].
The deleted region contains 50 genes and transcripts [Supplementary Table 1]; besides NSD1, six genes, including GPRIN1, SNCB, UNC5A, ZNF346, RGS14, and DBN1, are also highly associated with brain function, neural system development, neuron protecting or a nonprogressive cerebral disorder with mental retardation [13e20]. The other two genes, RNF44 and ARL10, are highly expressed in brain, although their function is unclear [21,22]. In general, individuals with microdeletion of NSD1 and neighboring genes in the 5q35 region present with less severe tall stature and more severe intellectual disability, compared to that in individuals with intragenic mutations [23].
According to the literature reviewed, two cases had deletion regions very similar to the case that we described here. One was a 3.5-year-old African-American girl, and the other was a 2.5-year-old African boy [24,25]. The clinical features were compared and summarized in Table 1. All of them had over growth, either at birth or at the time of reporting. They had long face, prominent and high forehead, sparse eyebrow, depressed nasal root, large ears, short philtrum, pointy chin, and macrocephaly. In neurological and psychiatric symptoms, all of them were . The deletion region of the African boy was the largest in these three cases; however, the African-American girl had more severe dysmorphisms, including cleft lip palate and patent ductus arteriosus (PDA), which were not found in the other two cases. Cleft lip palate was not reported in any Sotos syndrome except in this African-American girl; PDA was observed in 19% of microdeletion mutation type Sotos syndrome cases [5]. The number of gene and transcript deletions in the African boy was 52, 47 in the African-American girl, and 50 in our case. Most of these gene and transcript functions were unknown [Supplementary Table 1]. Although the deletion regions were very similar, the phenotypes were heterogeneous. More studies are needed to elucidate the functions and interactions of genes located in this region.
In our patient, some peculiar characteristic facial appearance was observed, including macrocephaly since birth, prominent forehead, high anterior hairline, pointy chin, and subtle down-slanting palpebral fissures, all of which are compatible with the diagnosis of Sotos syndrome. Other physical symptoms that are commonly described in Sotos syndrome' cases, such as seizures, scoliosis, cardiac anomalies, renal anomalies, and joint laxity, were not observed in this patient at this time, but we will closely monitor for these at future follow-ups. In conclusion, microdeletion or duplication is one of the most important causes of physical and mental developmental disorders. Although our case is generally compatible with typical Sotos syndrome, after detailed array-CGH analysis and comparison with other similar deletion cases, we can extend more data on genotype and phenotype correlation. In addition, Sotos syndrome is rare in Taiwan, and it is suggested that genetic analysis (array-CGH, target gene-NSD1 sequencing) should be considered early if symptoms of this case are observed. Genetic diagnostic results can provide more information for the patients' future development and genetic counseling for the family.

Conflicts of interest
The authors declare no conflict of interest. 5:176365486-176381909 e highly expressed in the brain NOP16 5:176383945-176388762 n/a n/a nucleolar protein HIGD2A 5:176388750-176389761 e a subunit of the cytochrome c oxidase complex (complex IV) CLTB 5:176392500-176416539 n/a n/a encodes one of two clathrin light chain proteins which are believed to function as regulatory AC010297.1 5:176439089-176439238 e FAF2 5:176448384-176510074 n/a n/a highly expressed in peripheral blood of patients with atopic dermatitis RNF44 5:176526711-176537402 n/a n/a expression in adult and fetal human brain regions CDHR2 5:176542510-176595974 e GPRIN1 5:176595801-176610156 n/a n/a wide distribution in human brain tissue and the central nervous system with highest expression in the spinal cord 5:177426793-177442901 n/a n/a G protein-coupled receptor kinase 6 PRR7 5:177446813-177456286 n/a n/a DBN1 5:177456935-177473637 n/a n/a neurite outgrowth, brain maturation; Drebrin (125 kD) expression was significantly decreased in the temporal and frontal cortex of both Down syndrome and Alzheimer disease patients, underlie cognitive dysfunction. PDLIM7 5:177483393-177497604 n/a n/a These proteins are involved in cytoskeleton AC145098.