Type IA Oromandibular-Limb Hypogenesis Syndrome: A Case Report and A Case Update

Hypoglossia is a rare congenital anomaly resulting in a small rudimentary tongue. It is classified under the oromandibular-limb hypogenesis syndrome and can be found in isolation (Type IA) but is more often associated with other congenital disorders, such as limb defects. Isolated hypoglossia cases are rare, and while feeding disorders are common, in some cases, neonatal airway obstruction is the most problematic. In the present report, we discuss two cases of newborns presenting with hypoglossia without limb deformities or visceral anomalies: one new case and a 10-year update of a previously reported case. These two cases highlight the variability in presenting symptoms and the challenges in diagnosis and management of a rare clinical entity. We focus on the discussion of early diagnosis, multidisciplinary management, and shared decision-making, with emphasis on the current therapeutic strategies available to the clinician and their limitations during the neonatal period. Early surgical multivector mandibular distraction osteogenesis can be proposed with minimal short- and long-term morbidity, pending a consistent follow-up. This clinical entity will require multidisciplinary team care into adult years.


Introduction
Isolated hypoglossia (also termed microglossia) [1] is a very rare congenital anomaly resulting in a "small rudimentary tongue." The assessment of the tongue size is subjective and requires a careful examination both at rest and during motion [2,3]. This may partly explain why the exact frequency of hypoglossia among newborns is unknown. Over the last two centuries, fewer than 30 cases of isolated hypoglossia have been reported in the literature. Hypoglossia can be found in isolation but is most commonly associated with other congenital disorders, involving the oromandibular complex (e.g., cleft palate, dental malformations, and maxillomandibular attachment) or the limbs. Hall [1] compiled these different clinical presentations and classified them as part of the oromandibular-limb hypogenesis syndrome (OLHS, MIM 103300) in which the only criterion for inclusion is hypoglossia. Type I OLHS presents either as isolated hypoglossia (Type IA) or aglossia (Type IB) [1]. Despite the initial common anatomical presentations, the two cases presented herein (one with long-term follow-up [4]) illustrate the differences in clinical course experienced by infants and children with hypoglossia. Few reports exist in the literature on isolated micro/hypoglossia and even fewer with early surgical intervention. The genetics consultation did not identify any underlying syndromic diagnosis. Echocardiogram, renal ultrasound, and chromosomal microarray were all normal. Early feeding and swallowing evaluation revealed normal gag, rooting, and sucking reflexes but an inability to actively extend the small rudimentary tongue. The infant was unable to manage her secretions or oral feeding bolus. Multidisciplinary discussions to determine the plan of care included members from neonatology, psychology, nutrition, speech therapy, genetics, otolaryngology, and craniofacial/plastic surgery. The infant remained dependent on nasogastric tube feeding and required continuous non-invasive ventilation with side positioning. Due to the shortened mandibular bodies and the V-shaped, narrow mandibular symphysis, the patient was deemed not a candidate for neonatal mandibular distraction osteogenesis (MDO). Ultimately, this necessitated tracheostomy tube placement, in conjunction with gastrostomy-tube (G-tube) placement at seven weeks of age. The child is enrolled in feeding intervention since birth to improve the oral motor function and strength. A pre-MDO planning maxillofacial computed tomography (CT) scan performed at six months of age revealed interval improvement in micrognathia. At this follow-up, she was also tolerating baby foods by mouth, taking full feeding via bottle, and minimally using the G-tube only for medications.

A 10-Year Update of a Previously Reported Case
A full-term infant presented with an isolated small anterior tongue. The child was noted to have severe feeding difficulty requiring a G-tube placement but no clinical signs of upper airway obstruction. At 16 months of age, the sleep study was normal, but the examination was notable for severe transverse constriction of the mandible and a small anterior 2/3 of the tongue with an otherwise normal tongue base. Given his severe feeding difficulties in the presence of glossoptosis ( Figure 2, Panel A), bilateral MDO was proposed in an effort to improve the feeding difficulty and potentially positively impact speech as this would allow for positioning of the small anterior tongue into the oral cavity. The child underwent MDO with multivector external devices at 17 months of age. Correction of the glossoptosis was observed ( Figure 2) with improvement in oral feeds. Removal of the MDO and gastrostomy tubes were successfully achieved three months later. In early childhood, he struggled with articulation errors, given the limited range of motion of the hypoplastic anterior tongue. He also had significant sialorrhea, possible mechanisms of which included impaired tongue movement, narrow/obliterated floor of mouth related to transverse mandibular hypoplasia, or impaired mental nerve sensation following MDO. He received onabotulinumtoxin A with good effect every six months until approximately age 4, at which point symptoms had improved. He underwent adenotonsillectomy for sleep-disordered breathing symptoms and required regular dental restorations under anesthesia.
The child received early intervention, speech and feeding services, and a set of tympanostomy tubes. His eustachian tube dysfunction had resolved by age 5, and other than receiving speech therapy through the school system for articulation errors, he had no developmental concerns and remained in age-appropriate grade level throughout his education. Figure 3 shows workup and intervention timelines.

Discussion
This report provides us with an insight into this rare clinical entity. Complete prenatal history and genetic microarray testing were negative for Case 2 and positive for marijuana exposure only in Case 1. While prenatal medication exposure (i.e., Diazepam and Tigan) [5] has been suggested to impact the development of the lingual and palatal structures between the fourth and eighth weeks of gestation [2,3], its causal relationship has not yet been proven. Given potentially associated malformations, early workup should include maxillofacial CT scan, renal ultrasound, chest x-ray, echocardiogram [6], brain ultrasound, and genetic evaluation as it is often pursued in patients with congenital anomalies of unknown etiology [1,[7][8][9][10][11][12][13][14][15][16]. Speech and swallow evaluation with a potential video swallow study can help complete the initial assessment ( Table 1).  For some, polysomnography may be considered. Although both cases presented with hypoglossia, transverse mandibular deficiency, and glossoptosis, their neonatal course and intervention strategy differed. While for Case 1, the airway symptoms ultimately required tracheostomy tube placement, Case 2's initial clinical presentation was dominated by feeding disorders. In our cases, the variation in tongue size and degree of glossoptosis were the main factors accounting for the difference in airway status.
A thorough assessment of the airways and swallowing function is critical for proper management. While direct laryngoscopy and bronchoscopy are the gold standards with regard to airways evaluation, a recent report highlighted the potential utility of ultrasonographic examination of the larynx in diagnosis (i.e., laryngeal abnormalities) and speech and swallowing function assessment [17]. This inexpensive, safe, and non-invasive procedure, that can be performed at the bedside, could be considered to assist clinicians in the decision-making strategy.
So far, the isolated microglossia cases described in the literature are presented with signs of PRS. As in any PRS case, the airway compromise can present early and require intervention. The first step in such cases is to opt for functional maneuvers aiming at relieving a part of the airway collapse. Prone or side-lying positioning and nasopharyngeal airways are the first steps and may allow for adequate ventilation in some cases. To counteract the impact of glossoptosis on the airway, surgical strategies may include tongue-lip adhesion, MDO, or tracheostomy ( Table 2). Choice of one procedure over the others will be driven by both the patient's anatomical and clinical status, the input from the different multidisciplinary healthcare specialists, and the caregivers' preferences. However, contrary to patients with PRS in whom MDO may be considered within the first weeks after birth, the impaired mandibular development in hypoglossia/micrognathia cases may prevent the placement of a distraction device and can complicate the planned distraction vectors. In such a case with airway compromise, the early and safest option is deemed to be a tracheostomy tube placement, as done in Case 1. In both cases, the constricted mandible associated with hypoglossia limited the infants' oral motor function and bolus propulsion abilities, mandating a nasogastric and then ultimately G-tube placement.  Palatal, mandibular, and tongue development are intertwined [18]. The transverse mandibular deficiency observed with hypoglossia is related to their shared origin from the mandibular arch and subsequent coordinated development and growth [19]. The arched palate is suggested to be secondary to the missing mechanical stimulation from the anterior two-thirds of the tongue [18]. To address the impact of hypoglossia on feeding, the most common initial strategy is the placement of a feeding tube. However, previous reports mentioned the release and elongation of the tongue using a full-thickness skin graft that may help release the tongue and improve swallowing function or the use of a palatal drop prosthesis to shorten the distance to the palate and help with bolus propulsion [4]. In the literature, orthognathic surgery with arch expansion and bone grafting, orthodontic treatment, and/or mandibular distraction (internal or external with or without vertical symphyseal osteotomy) were considered in middle/late childhood to correct the transverse discrepancy between the maxillary and mandibular arches, optimize mastication, and swallowing functions [4,12,14].
To date, only one report mentioned early MDO in a five-week-old infant with microglossia. However, this patient had other associated anomalies, and the MDO was similar to a PRS case with longitudinal distraction to improve airway patency. Despite this, transverse discrepancy persisted, and no long-term follow-up assessment is yet available [18]. In the present report, we highlight the variations that the hypoglossia itself may present with regard to the mandibular and airways status as well as provide a longitudinal view of multidisciplinary care after early multivector MDO. Multivector distraction within the first two years of life can help minimize the impact of hypoglossia on both the airway patency (by correcting the impact of associated glossoptosis) and feeding abilities. Although gradual mylohyoid muscle hypertrophy was reported as a compensatory factor for the floor of the mouth to reach the palate and help with swallowing, the patients presented herein did not exhibit such features, probably due to their young age at intervention. Malocclusion and impact on speech are commonly noted in the literature [7,9,12,15], as in the present report, with a tendency for slurred and nasal tone speech. Such observation strengthens the possible role of hypoglossia on articulation mechanisms either through a direct influence with the lack of proper tongue posture (no contact with the palate) or indirectly through its interaction with craniofacial skeletal growth and dental arch formation [20].