3. Discussion
The general features of 22q11.2 DS vary widely (more than 180 phenotypic presentations) and includes Di George’s syndrome, Shprintzen’s syndrome as well as Cayler cardio-facial syndrome. The syndromes were named separately after their first description by the author. Later, with the advancements in the diagnostic methods in the field of genetics, it was found that 22q11.2 chromosome was deleted in all these syndromes. They are currently grouped under “the 22q11.2 deletion syndromes”, as it is difficult to choose a single term.
22q11.2 DS is one of the most frequently encountered interstitial deletion syndromes in the population, with an estimated frequency of 1/4000-5000 (Scambler, 2000). Though usually sporadic and autosomal dominant inheritance, it has been reported in 10-20% of the patients (Bassett et al., 2011).
The chromosome 22q11 region is very unstable with misalignment of chromosome-specific low-copy repeats (LCR22A-H) during nonallelic homologous recombination, leading to the deletion of 22q11.2 region (Burnside, 2015). Approximately 90% of patients with 22q11DS have a 1.5~3Mb deletion (Burnside, 2015; Yagi et al., 2003). The haploinsufficiency of genes located at 22q11.2, especiallyTBX1 , can disturb the early morphogenesis of many organs including the thymus, parathyroid gland and facial structures. This explains as to why there are wide clinical manifestations like cardiac defects, thymic hypoplasia, abnormal facial features, cleft palate, and hypocalcemia associated with it (Yagi et al., 2003).
The cause of hypoplasia of the depressor anguli oris muscle still remains to be elusive, though previous studies postulated intrauterine molding or subclinical viral infections as the cause. This finding needs further confirmation. Lahat et al. (Lahat, Heyman, Barkay, & Goldberg, 2000) reported a prospective study, wherein 17 out of 5532 infants had ACF. There were no noxious obstetric perinatal factors identified and no family history of hereditary diseases in all the cases. In our case, we also found no maternal infection and no family history of hereditary or systemic diseases associated with ACS.
Hypoparathyroidism and hypothyroidism are commonly observed in patients with 22q11.2 deletion and requires much attention. Hypoparathyroidism is the first hormonal disturbance recognized in DGS and is documented by aplasia and hypoplasia of the parathyroid glands during surgery or autopsy. Furthermore, hypocalcemia can occur transiently during the neonatal stage with symptoms of seizures, tremors, or tetany, which mainly occur due to low parathyroid reserve and abrupt cessation of maternal calcium supply after birth. In our case, serum calcium level was normal (2.3mmol/L, reference rage, 2.1-2.7 mmol/L), no hypocalcemic symptoms of seizures, tremors, or tetany were observed on admission, which ruled out the possibility of hypocalcemia due to hypoparathyroidism. Although hypocalcemia may not be present during the neonatal period (Pawar, Sharma, Srilakshmi, Reddy Chejeti, & Pandita, 2015), studies have shown that it can occur at any time during childhood (Friedman, Rienstein, Yeshayahu, Gothelf, & Somech. 2016; Fu, Leung, Kao, & Yeh, 2015), adolescence (Yoo, Kim, Cho, Kwon, & Yoo, 2017) and even in adulthood (Fung et al., 2015; Maldjian & Sanders, 2018). This is likely due to the recurrence of hypoparathyroidism precipitated by increased metabolic demand and acute illness during pregnancy, surgery, infection, or any physiologic stress conditions. Regular lifelong follow-up of calcium, magnesium, and PTH levels are required in patients with 22q11DS (Cheung, George, Costain, Andrade, Chow, Silversides, & Bassett, 2014). Calcium and vitamin D supplements are recommended to patients with 22q11DS, regardless of whether they have been diagnosed with hypocalcaemia or not. However, iatrogenic hypercalcemia resulted in renal calculi and renal failure, and so should be avoided (Fung et al., 2015).
Immunodeficiency has been reported in 80% of the patients with 22q11 syndrome. As a result of thymic hypoplasia, cell-mediated immunity is usually involved with 22q11DS, decreasing the T-cell numbers and functions. However, disorders of humoral immunity might also occur. Waters et al. (Waters, Peterson, & LaRussa, 2007) reported a case of pneumonia in a 13-month-old male child with partial DGS, and the child died after inadvertently receiving live viral vaccines. Recently, Matsuoka (Matsuoka et al., 2019) reported the first case of a teenage patient with chromosome 22q11.2 DS who died due to overwhelming post-splenectomy infection (OPSI) by Streptococcus pneumoniaedespite appropriate prevention by pneumococcal vaccine. As such, it is appropriate to check immunoglobulin levels in the patient before vaccinations.
Congenital heart defects are one of the main clinical features of 22q11DS. Although serious cardiac anomalies were present in most of the patients in earlier studies, their prevalence accounted for about 40% according to the recent papers (Fung et al., 2015). Interestingly, our patient had ventricular septal defect and two atrial septal defects which warranted ongoing follow-up visists.
Some follow-up studies revealed that the frequency of psychomotor retardation and speech disorders was increased (Cancrini et al., 2014). However, information regarding long-term outcomes and older age ranged in ACS has been limited in China. Our patient showed a normal neonatal behavioral neurological assessment (NBNA) score at a corrected gestational age of 41 weeks and his physical index was between P10-P90, but he still had ACF. During the final evaluation, he was aged 2 years 6 mo, had developmental delay (height: 80cm; and body weight: 11kg) and speech deficits. However, the patient’s intellectual level, cognitive and adaptive functioning and motor function were normal. The patient had undergone intracardiac repair the prior month which necessitated ongoing follow-up visits. The best case scenario involves early interventions for developmental delay and learning difficulties. Parents required counseling due to long-term outcomes, as deletion of 22q11.2 is associated with learning difficulties and mental retardation.
Previously, karyotyping results by GTG banding were normal in most of the ACF patients. Recently, more sophisticated techniques such as FISH have been replaced by karyotyping studies in most of the laboratories. It is therefore not surprising that several ACF cases with chromosome 22q11 microdeletions have been or continue to be reported (Pawar, Sharma, Srilakshmi, Reddy Chejeti, & Pandita, 2015). Some authors, therefore, suggested that newborns with ACF require additional screening of 22q11.2 DS (Pasick, McDonald-McGinn, Simbolon, Low, Zackai, & Jackson, 2013). In our case, genetic investigations were performed to exclude any underlying syndrome caused by 22q11 deletion. Notably, DNA high throughput sequencing analysis revealed two microdeletions of chromosomes 22q11.21 and 11p15.4, respectively. This, coupled with the clinical presentation confirmed the diagnosis of ’ACF’ as a result of hypoplasia of the depressor anguli oris muscle.
Previous studies have reported that children diagnosed with Cayler Cardio-facial syndrome have an underlying condition called 22q11.2 DS, in which a small part of chromosome 22 is absent. More importantly, we detected additional chromosomal microdeletions in 11p15.4 in our patient. ACS is traditionally diagnosed using FISH with commercial probes. It is extremely accurate but limited to only one single-target sequence. Interestingly, our results showed the effectiveness of DNA high throughput sequencing, which overcame the limitations of FISH in terms of diagnostic yield and allowed whole genome screening and detection of a larger number of deletions and/or duplications in ACS patients.
In conclusion,our report reinforces that facial phenotypic and cardiac anomalies are manifestations associated with ACS. However, confirmation of this disease requires further genetic investigations. Apart from a microdeletion of chromosome 22q11.21, a novel microdeletion of chromosome 11p15.4 was found in our case. We, therefore, suggest that newborns with ACS should be screened with DNA high throughput sequencing analysis across the whole genome, which is more advantageous over FISH technique and could contribute to further research.