Mohr syndrome is a rare, inherited genetic condition that primarily affects the development of the face, mouth, and digits. First described in 1941 by Norwegian geneticist Otto L. Mohr, this disorder is part of a larger group of conditions known as orofaciodigital syndromes (OFDS). It is characterized by a distinct combination of physical traits present at birth, though its features can vary among affected individuals.
Physical Characteristics of Mohr Syndrome
The most apparent indicators of Mohr syndrome involve the structure of the face and mouth. A key feature is a lobed or partially cleft tongue, which can appear to have multiple lobes or a deep groove down the middle. Small, noncancerous growths or nodules, known as hamartomas, may also be present on the tongue. Another common oral sign is a high-arched or cleft palate, where the roof of the mouth has not fused properly during development.
Facial characteristics often include widely spaced eyes, a condition called hypertelorism, and a flat nasal bridge. The upper and lower jaws may be underdeveloped, a state referred to as maxillary and mandibular hypoplasia. The presence of an unusually thick or prominent frenulum, the tissue connecting the lip to the gum, is also a frequent finding.
Abnormalities of the limbs are common. Polydactyly, the presence of extra fingers or toes, is common. A specific and highly characteristic trait of Mohr syndrome is the duplication of the big toe, known medically as preaxial polydactyly of the hallux. Conversely, some individuals may have unusually short fingers and toes, a condition called brachydactyly.
Conductive hearing loss is a significant concern, often resulting from malformations of the tiny bones within the middle ear, known as the ossicles. This type of hearing impairment occurs because sound waves are not conducted efficiently from the outer ear to the inner ear. The combination and severity of all these physical traits can differ substantially from one person to another.
Genetic Basis and Inheritance Patterns
Mohr syndrome is categorized as Orofaciodigital Syndrome Type II (OFDS II) and is inherited in an autosomal recessive pattern. This means that for an individual to be affected, they must inherit two copies of a non-working gene from each parent. Parents who each carry one copy of the mutated gene are known as carriers and do not show any signs of the condition themselves.
When both parents are carriers, there is a 25% chance with each pregnancy that the child will inherit two non-working genes and be affected by Mohr syndrome. There is a 50% chance the child will inherit one copy and become a carrier, just like the parents. Finally, there is a 25% chance the child will inherit two working copies of the gene and be neither affected nor a carrier.
While the precise genetic cause of Mohr syndrome is not identified in all cases, research has linked some instances to mutations in specific genes. One such gene implicated in the condition is PIBF1. Mutations in this gene disrupt its normal function, leading to the developmental abnormalities seen in the syndrome.
Diagnostic Process
The diagnosis of Mohr syndrome is primarily based on a thorough clinical evaluation. The presence of a lobed tongue, polydactyly of the big toe, and specific facial traits are strong indicators.
To supplement the physical examination, imaging studies are often employed. X-rays of the hands and feet can provide clear evidence of polydactyly and other bone malformations, such as shortened digits. Skull X-rays may be used to assess the development of the jaw and other facial bones. In some instances, features of the syndrome can be detected before birth through prenatal ultrasound, which may reveal limb abnormalities or facial clefts.
Genetic testing can be used to confirm a diagnosis, particularly if a mutation in a known associated gene like PIBF1 is suspected. However, since not all genes related to Mohr syndrome have been identified, genetic testing may not provide a definitive answer in every case.
Managing Health and Development
Management of Mohr syndrome focuses on addressing the specific health and developmental challenges that arise from its physical characteristics. There is no cure for the underlying genetic condition, so care is supportive and tailored to the individual’s needs. This requires a multidisciplinary team of specialists to coordinate treatment and provide comprehensive support.
Surgical interventions are frequently necessary to correct structural abnormalities. For example, surgery can repair a cleft lip or palate, which helps improve feeding and speech development. The removal of extra fingers or toes (polydactyly) is another common procedure, often performed in early childhood.
Due to the oral anomalies, extensive dental and orthodontic treatment is often required to address issues with teeth alignment and jaw structure. For those with conductive hearing loss, consultations with an audiologist are necessary. Treatment may involve the use of hearing aids or other assistive devices to improve auditory function. Speech therapy is also a common intervention, helping individuals overcome challenges related to the structure of their palate and tongue.