What Is Boucher-Neuhäuser Syndrome?
Boucher-neuhäuser syndrome is an uncommon condition that affects sexual development, vision, and movement. It belongs to a group of neurological disorders known as PNPLA-6-related disorders, which share a common genetic cause and exhibit homogeneous characteristics. It can occur as a result of mutation, and inheritance can follow an autosomal recessive pattern. This means that the parents of autosomal recessive condition each will possess a copy of the mutated gene and do not exhibit any symptoms of this disease. Individuals with Boucher-neuhäuser syndrome typically exhibit problems like ataxia, chorioretinal dystrophy, and hypogonadotropic hypogonadism. Other medical problems experienced by the affected individuals include spasticity (muscle stiffness), cognitive impairment (difficulties with processing, recalling, or learning information), and dysarthria (speech impairment).
What Is the Prevalence of Boucher-Neuhäuser Syndrome?
In 1989 Limber et al. identified the syndrome in a family and identified it as a distinct single-gene disorder. Other researchers like Fok et al. in 1989 and Salvador et al. in 1995 reported similar cases with varying ages of onset and symptom progression.
In 1997, Rump et al. noted that additional features beyond the triad of symptoms may make the diagnosis of Boucher-neuhäuser syndrome challenging.
In the year 2014, Synofzik et al. described cases of Brazilian siblings born to consanguineous parents where visual impairment due to chorioretinal dystrophy appeared in early life, which was followed by ataxia and hypogonadotropic hypogonadism. The phenotype of the disease was also seen in other families and reported variability in symptoms. In 2014 Topaloglu et al. reported six patients from related families with ataxia and pubertal failure, and everyone carried biallelic mutations in the PNPLA6 gene, which is the known cause of this disease. Some patients did not report any visual symptoms which indicate variations in the disease manifestations.
What Are the Features of Boucher-Neuhäuser Syndrome?
Boucher-neuhäuser syndrome has three main features, namely hypogonadotropic hypogonadism, ataxia, and chorioretinal dystrophy. The key features of Boucher-Neuhäuser syndrome can manifest anytime from infancy to childhood, with at least one feature typically becoming apparent during adolescence. While ataxia often emerges as the first symptom, vision problems or delayed puberty can also serve as early indicators. Over time, vision and movement issues gradually worsen and can result in blindness, or a wheelchair can be needed in severe cases.
Hypogonadotropic Hypogonadism: Affected individuals who have impairment in the hormones responsible for sexual development. This condition can cause a delay in the typical signs of puberty, like deepening voice and facial hair growth in males and the onset of menstruation and breast development in females. A few affected individuals can exhibit hormone-related short stature. Eunuchoidism, characterized by a lack of sexual characteristics, libido loss, and infertility, is also seen in Boucher-neuhäuser syndrome.
Ataxia: Ataxia is another important aspect, as there can be difficulties in balance and coordination as a result of atrophy or degeneration of cerebellar cells since the cerebellum is part of the brain that is responsible for coordination and movements. Affected individuals typically exhibit unsteady gait and frequent falls.
Chorioretinal Dystrophy: The third distinctive feature involves vision problems due to eye abnormalities commonly presenting as chorioretinal dystrophy. Affected individuals have issues with the retina as they will be light-sensitive, and the adjacent choroid at the back of the eye results in vision impairments. They also exhibit abnormal eye movements, including nystagmus, which is characterized by involuntary side-to-side eye movements.
What Is the Etiology of Boucher-Neuhäuser Syndrome?
Boucher-Neuhäuser syndrome is mainly caused by a mutation in the PNPLA6 gene, which is currently the one known factor responsible for causing this condition. However, in the remaining cases, researchers suspect there might be unidentified mutations in the PNPLA6 gene or alterations in other genes that precipitate this syndrome. As of now, researchers fully do not understand how mutations in the PNPLA6 gene result in various features evident in Boucher-neuhäuser syndrome and also other spectrum diseases related to the PNPLA-6 gene. The NTE protein, essential for lipid breakdown, plays a significant role in maintaining the stability of cell membranes, particularly in the nervous system. Additionally, it appears to be involved in the release of pituitary hormones, where changes in the cell membrane and lipid components are necessary for this process. Proper functioning of the pituitary gland is important in sexual development and growth.
Boucher-neuhäuser syndrome is caused due to more than a dozen mutations in the PNPLA-6 gene. The primary function of the PNPLA6 gene is to instruct for producing a protein called NTE (neuropathy target esterase). NTE plays a major role in regulating specific lipids that form the outer membrane surrounding cells. There should be a balance maintained in these lipids to ensure the stability and function of the cell membranes. NTE is particularly numerous in the nervous system and is believed to be involved in preserving the stability of the membranes surrounding neurons. Additionally, it appears to be involved in the release of pituitary gland hormones. The pituitary gland is present at the brain base and responsible for producing hormones, including those that influence sexual development and growth.
It is suspected that mutations in the PNPLA6 gene disrupt the normal NTE function. However, the precise mechanism by which these mutations cause Boucher-neuhäuser syndrome remains unclear. One hypothesis suggests that impaired metabolism of a specific lipid called lysophosphatidylcholine leads to an imbalance in cell membrane lipids. This imbalance could potentially damage neurons, giving rise to the movement and vision problems that are characteristic of Boucher-neuhäuser syndrome. Furthermore, it may also affect the release of hormones involved in sexual development, which explains the observed delayed puberty in affected individuals.
Boucher-neuhäuser syndrome occurs as a result of mutations in the PNPLA6 gene that plays a role in producing NTE protein. These negatively impact the NTE function resulting in the distinctive symptoms of this disease. The exact mechanism by which these mutations give rise to the characteristic features of this disease is not fully known. Unfortunately, there is no known cure for Boucher-neuhäuser syndrome, and management includes symptomatic treatment and providing supportive care for the affected individuals.