Could replenishing a sex hormone improve cognition in Down’s syndrome? If given the right way, gonadotrophin-releasing hormone (GnRH) can do just that, according to researchers led by Vincent Prevot and Paolo Giacobini, University of Lille, France, and Nelly Pitteloud, University of Lausanne, Switzerland. In the September 2 Science, they reported that in a mouse model of DS, GnRH-expressing neurons begin to wither when the animals are pups, causing loss of smell and cognitive trouble during puberty. Pumping pulses of the hormone into adult mice restored olfaction and improved cognition. In a pilot trial, brain connectivity and cognition improved slightly in seven adults with DS who took GnRH for six months. A Phase 2 trial is slated to begin this fall.

  • In a mouse model of DS, loss of gonadotrophin-releasing hormone precedes cognitive decline.
  • Injecting mice with GnRH improved cognition, restored olfaction.
  • In a DS pilot trial, pulses of GnRH improved brain connectivity and cognition.

“This paper is a tour de force with extensive and well-designed experiments in the Ts65Dn mouse model for DS to prove the role of GnRH [in olfactory and cognitive deficits] and understand the mechanisms,” wrote Juan Fortea, Hospital of Sant Pau, Barcelona, Spain (full comment below).

Shahid Zaman, University of Cambridge, U.K., agreed. “This work supports the suspicion that GnRH and its receptor are expressed outside the hypothalamus and have functions beyond reproduction,” he told Alzforum.

People with DS carry three copies of chromosome 21 and experience a wide range of symptoms, including intellectual disability, progressive memory loss, a waning sense of smell, sex hormone deficiency, and fertility issues. The last two stem from a dearth of GnRH. During puberty, neurons in the hypothalamus normally crank out GnRH to stimulate production of luteinizing hormone or follicle-stimulating hormone from the pituitary. In most teens with DS this spike never happens and GnRH levels remain low.

Beyond the sex hormones axis, GnRH is suspected of having other functions in the brain. Prevot and Giacobini previously reported that human GnRH-expressing neurons stretch their processes out from the hypothalamus into the hippocampus and cortex, suggesting a role in learning and memory (Casoni et al., 2016; Skrapits et al., 2021). Others found that, in aged mice, supplementing with the hormone improved cognition and neurogenesis (May 2013 news). Could the withering of GnRH neurons contribute to intellectual disability in DS? And if so, would boosting levels in the brain improve cognition?

To find out, co-first authors Maria Manfredi-Lozano and Valerie Leysen of U Lille and Michela Adamo of U Lausanne first turned to a mouse model of DS. Ts65Dn mice carry three copies of chromosome 16, which includeS regions homologous to human chromosome 21. Like most people with DS, these mice are infertile, have memory problems, and lose their sense of smell.

Newborn Ts65Dn pups sniffed out milk as well as their wild-type counterparts. However, unlike wild-type mice, both 1-month-old prepubescent and 3-month-old adult DS mice had trouble smelling. They could not distinguish novel odors from familiar ones, for example, the smell of orange blossoms versus a citrus scent. As for memory, failure to recognize novel objects began after puberty.

Did these smell and memory problems coincide with GnRH neuron loss? Indeed, immunohistochemistry of brain tissue slices from Ts65Dn mice revealed normal distribution and number of GnRH-positive neurons at birth but a severe decline after puberty. Three-dimensional imaging of whole adult brains showed GnRH-expressing neurons in the hippocampi and cerebral cortices in wild-type, but not Ts65Dn, mice (see image below). The authors believe that a waning sense of smell foretells the loss of neurons that make GnRH, and that a drop in this hormone triggers pubescent cognitive decline.

Missing Neurons. Imaging of the whole brain from 3-month-old wild-type mice (left) showed GnRH-expressing neurons (white) in the hypothalamus (top) and surrounding hippocampal tissue (bottom, arrows). These cells are all but absent from 3-month-old Ts65Dn mice (right). [Courtesy of Manfredi-Lozano et al., Science, 2022.]

Could boosting GnRH levels compensate for this neuron loss? Indeed, a single intraperitoneal injection of the hormone into adult Tsg5Dn mice normalized olfaction two hours later, while three jabs over two days restored cognition.

Because a constant stream of the hormone desensitizes its receptor, ultimately shutting down signaling, the researchers next opted to mimic the pulses of GnRH released by the hypothalamus. They implanted subcutaneous minipumps containing GnRH into 6-month-old mice. These either released the hormone continuously or in 10-minute pulses every three hours. After 15 days of pulsed GnRH, mice could discriminate new smells and objects from known ones, while mice that had continuous GnRH could not. In fact, continuous release worsened olfaction and novel object recognition. These results suggested that restoring pulsatile physiological GnRH signaling, even in adult mice, improves cognition.

Many researchers praised the mouse data. “It strongly supports the potential role of GnRH deficits [in] subsequent neuroanatomical disruptions and, presumably, the intellectual disability observed in persons with DS,” Michael Rafii, University of Southern California, San Diego, wrote (full comment below).

Could replenishing GnRH improve cognition in people with DS? The scientists recruited seven men who had DS, and a poor sense of smell, from Lausanne University Hospital for an open-label pilot study. They ranged from 20 to 50 years old. For six months, a subdermal pump infused GnRH once every two hours to mimic pulse frequency in healthy men. This hormone pump is used to treat GnRH deficiency, a disease called Kallmann syndrome (Raivio et al., 2007). Participants received structural and functional MRI scans and took the Montreal Cognitive Assessment before and after treatment. The researchers chose the MoCA because it is short and manageable for people with DS.

At baseline, structural MRI showed less myelin in the thalamus and corticospinal tract than in age-matched controls and a smaller than normal thalamus, cerebellum, and cingulate gyrus. Resting-state fMRI revealed altered default mode network (DMN) connectivity. All participants had impaired cognition on the MoCA, with baseline scores ranging widely from 4 to 22 out of 30.

After GnRH treatment, the visual and sensorimotor portions of the DMN became better connected (see image below). MoCA scores improved by a few points in six participants, particularly in visuospatial, executive function, and attention subscores. Memory scores, olfaction, and brain structure remained unchanged. Overall, the authors concluded that the pulsed GnRH therapy might improve cognition in people with DS.

Boosting Connectivity, Cognition. In seven people with DS, brain connectivity after six months of treatment with GnRH was better (top, right) than at baseline (top, left). Scores on the MoCA and its visuospatial, executive, and attention, but not memory, indices also improved slightly (bottom). [Courtesy of Manfredi-Lozano et al., Science, 2022.]

“This work opens new avenues to pursue as we try to understand the impact of chromosome 21 trisomy on neurodevelopment while also providing a rational mechanism for testing existing therapeutics to enhance cognition in this population,” wrote Rafii. Zaman thought this work offered a unique approach to improving cognition. “GnRH replacement puts a different spin on cognitive remediation by evoking compensatory mechanisms rather than reversing a disease pathway,” he noted.

However, other researchers interpreted the clinical results cautiously. “This pilot study shows that the GnRH pump is feasible to use in people with DS, but you cannot determine treatment efficacy without a placebo control,” Elizabeth Head, University of California, Irvine, told Alzforum. Zaman agreed, wondering if the modest MoCA improvements were due to the practice effects of repeated testing. Prevot said they used two different versions of the MoCA before and after treatment to avoid practice effects.

Still, the MoCA was not designed for people with intellectual disabilities and has not been validated in DS. “This was evident as most participants scored in the mild cognitive impairment range or below,” Head noted. Fortea agreed. “Most individuals [with DS] will perform at floor levels,” he wrote. Mark Mapstone, also at UC Irvine, noted that the MoCA is a global cognitive screening measure, not a comprehensive evaluation of cognitive domains. Scientists are developing cognitive tests tailored to DS or confirmed to be sensitive in this population (May 2021 news).

“This study was not powered to determine GnRH’s effect on memory and other domains,” said Mapstone. Pitteloud said they are planning a placebo-controlled Phase 2 trial, aiming to enroll 60 to 80 adults with DS and poor senses of smell. All will wear a subdermal pump—half will get GnRH, half saline—for six months. The primary outcome is a change in MoCA score, though Pitteloud said they are open to also using DS-specific tests. Secondaries include the change in functional MRI, sense of smell, and fluid markers of amyloidosis. The trial is slated to begin in November in Lausanne.—Chelsea Weidman Burke

Comments

  1. Manfredi-Lozano et al. show the potential of restoring olfactory and cognitive performance with pulsatile GnRH therapy in individuals with DS (and maybe even for the general elderly population). This paper presents very novel findings, in my opinion. First, the role of GnRH in extrahypothalamic areas to understand the olfactory and cognitive deficits in individuals with DS. The paper is a tour de force with extensive and well-designed experiments in the Ts65Dn mouse model for DS to prove the role of GnRH (and understand the mechanisms). Second, the focus on understanding the cognitive deficits in DS had traditionally been in the prenatal neurodevelopmental period and in the AD-related cognitive decline much later in adult life. This paper thus emphasizes the need to focus on the postnatal brain maturation in the infantile and, even more surprisingly to me, pubertal and postpubertal periods to fully understand the cognitive deficits associated with DS.

    Despite previous and ongoing efforts, there is no pharmacological therapy to improve cognition in DS. Moreover, and although the bulk of the experiments are performed in Ts65Dn mice, the authors provide a compelling rationale for a potential use of GnRH replacement for other conditions, including AD. The fact that pulsatile GnRH is a safe treatment approved for other indications should accelerate the clinical development and the trials needed to prove the efficacy of this therapy.

    We should, nonetheless, give a word of caution since the data in humans came from a very small pilot study in seven men. Several clinical trials in different age ranges in DS (and other trials in the general population) should be carried out to assess the efficacy of pulsatile GnRH to enhance cognitive function and potentially even prevent AD.

    The MoCA, which is commonly used in the general population, is not well suited to assess cognitive function in DS as most individuals will perform at floor levels. The data in humans in the work comes from a proof-of-concept, very small pilot study in seven men. The (much) larger placebo controlled clinical trials needed to prove the efficacy of this therapy should indeed use adapted cognitive and clinical measures.

  2. Secretion of gonadotropin-releasing hormone by the hypothalamus, particularly at high levels during puberty, leads to production of testosterone in boys and estrogen in girls. In children with Down’s syndrome, this pubertal increase never really occurs due to dysregulated GnRH-production and is thought to be the cause of the infertility observed in men and the subfertility in women.

    Manfredi-Lozano et al. show that GnRH-producing neurons also project to the hippocampus and that this connectivity is abnormal in the Ts65dn mouse. They identify five microRNAs encoded on chromosome 21, and therefore have increased expression in DS, which leads to dysregulated GnRH production. Through a meticulous series of experiments, they show that they can rescue this dysregulated neuronal connectivity using pulsatile GnRH and improve memory function in the Ts65dn mouse.   

    Moving into human studies based on the animal model data, they used small minipumps that were placed subdermally in seven adult men with DS to deliver pulsatile (q 2hrs) GnRH for six months. They report finding similar improvements in both brain connectivity on MRI as well as enhancements in cognition.

    The authors should be congratulated on this work. It opens new avenues to pursue as we try to understand the impact of trisomy of chromosome 21 on neurodevelopment while also providing a rational mechanism for testing existing therapeutics to enhance cognition in this population.

    The animal data is well-controlled and is strongly supportive of the potential role of GnRH deficits, subsequent neuroanatomical disruptions and, presumably, the intellectual disability observed in persons with DS.

    Whether this GnRH dysfunction plays a role in the development of AD pathology in DS remains unclear. The results of the pilot study will need to be replicated in a larger number of individuals, perhaps using a modified study design to confirm any cognitive benefit. The Montreal Cognitive Assessment (MoCA), although well-validated in the general population, has not been validated in persons with DS. CSF and plasma biomarkers for AD pathology in older adults could be carefully assessed. Finally, a randomized, placebo-controlled, double-blinded study would help us firmly understand the impact of GnRH on cognition in adults with DS. The participant age range, comorbidities, and concomitant medications would all need to be carefully considered in the study design.

    Whether GnRH could be used in the general population depends upon whether the GnRH dysfunction observed in DS also occurs as part of old age or sporadic AD. That is, if GnRH neurons that project to the hippocampus lose their capacity to release GnRH with age or are deleteriously affected by plaques and tangles.

  3. This suggests that GnRH replacement improves cognition in the TsDn65 preclinical models of Down’s syndrome, and that this therapy may have translational value in humans with DS. Even though GnRH has been used to treat other conditions, the proposed use of GnRH as a treatment for cognitive impairment in DS based on findings derived from a genetic preclinical model may lead to a therapeutic dead end, similar to the lack of clinical efficacy of anti-amyloid vaccination therapies based in preclinical model studies of Alzheimer’s disease.

    However, in this study, the authors enrolled seven individuals with DS (20 to 50 years of age) in an open-label pilot study to assess the effect of six-month pulsatile GnRH therapy on cognitive and olfactory function. Cognitive function was assessed using the MoCA test for dementia, which, in my opinion, is not a good test of cognition in people with DS. The authors should have used other tests specifically designed to test cognitive abilities due to the unique cognitive profile found in people with DS. Perhaps a more appropriate battery would have been the Arizona Cognitive Test Battery (ACTB) that includes normative data from individuals whose performance is several standard deviations below average, with a lower floor performance than many traditional cognitive assessments. This factor is essential for a measure to be sensitive to change when administered to individuals who have intellectual deficits such as DS. Moreover, the need to provide GnRH over the life span of an individual with DS would be a daunting task with unknown clinical and physiological consequences.

  4. Although this is an interesting approach, which may open up new avenues for investigating the cognitive impairments associated with Down’s syndrome, I see several issues with this paper.

    First, the animal model experiments are at best preliminary, as they are based on very small groups (n=4 in some cases), and thus do not allow for exploration of sex differences, which are important in understanding the effects of GnRH. Furthermore, the experiments make use of an older mouse model (Ts65Dn). It includes triplicated genes that are not on human chromosome 21, and focuses on phenotypes not universally recognized in Down’s syndrome, such as olfactory deficits. Much more preclinical work needs to be done before the findings can be applied in human studies.

    Although the authors included data from a small study in young men with Down's syndrome (n = 7), the participants (and possibly also raters) were not blinded, and a control group is not included. The cognitive measure (MoCA) used to show supposed cognitive improvement on treatment with pulsatile GnRH therapy was designed for neurotypical older adults, and is not used to determine cognitive abilities in individuals with Down’s syndrome. People with Down's syndrome typically have significant floor effects on such tools unless adapted for this population and then validated (which is not the case for the MoCA). In addition, the treatment was short-term. In summary, the result of the human experiment is not meaningful.  

    It is important not to confuse the neurodevelopmental aspects of Down's syndrome (in this case, lifelong cognitive impairment) from the later effects of Alzheimer's pathology, which leads to cognitive decline from a neurodevelopmental baseline. This study does not include experimental data on Alzheimer's disease in Down's syndrome. 

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References

News Citations

  1. Do Microglia in the Hypothalamus Drive Aging?
  2. Gearing Up for Down’s Syndrome Clinical Trials

Research Models Citations

  1. Ts65Dn

Paper Citations

  1. . Development of the neurons controlling fertility in humans: new insights from 3D imaging and transparent fetal brains. Development. 2016 Nov 1;143(21):3969-3981. PubMed.
  2. . Reversal of idiopathic hypogonadotropic hypogonadism. N Engl J Med. 2007 Aug 30;357(9):863-73. PubMed.

External Citations

  1. Phase 2 trial

Further Reading

Primary Papers

  1. . GnRH replacement rescues cognition in Down syndrome. Science. 2022 Sep 2;377(6610):eabq4515. PubMed.