Cerebellar hypoplasia and quadrupedal locomotion in humans as a recessive trait mapping to chromosome 17p

Modifications of the locomotor system in habitually quadrupedal humans

The acquisition of habitual bipedal locomotion, which resulted in numerous modifications of the skeleton was a crucial step in hominid evolution. However, our understanding of the inherited skeletal modifications versus those acquired while learning to walk remains limited. We here present data derived from X-rays and CT scans of quadrupedal adult humans and compare the morphology of the vertebral column, pelvis and femur to that of a bipedal brother. We show how a skeleton forged by natural selection for bipedal locomotion is modified when used to walk quadrupedally. The quadrupedal brother is characterised by the absence of femoral obliquity, a very high anteversion angle of the femoral neck, a very high collo-diaphyseal angle and a very reduced lordosis. The differences in the pelvis are more subtle and complex, yet of functional importance. The modification of the ischial spines to an ischial ridge and the perfectly rounded shape of the sacral curvature are two unique features that can be directly attributed to a quadrupedal posture and locomotion. We propose a functional interpretation of these two exceptional modifications. Unexpectedly, the quadrupedal brother and sister show a greater angle of pelvic incidence compared to their bipedal brother, a trait previously shown to increase with learning to walk in bipedal subjects. Moreover, the evolution from an occasional towards a permanent bipedality has given rise to a functional association between the angle of pelvic incidence and the lumbar curvature, with high angles of incidence and greater lumbar curvature promoting stability during bipedal locomotion. The quadrupedal brother and sister with a high angle of incidence and a very reduced lordosis thus show a complete decoupling of this complex functional integration.

Neurodevelopmental Syndrome with Intellectual Disability, Speech Impairment, and Quadrupedia Is Associated with Glutamate Receptor Delta 2 Gene Defect

Bipedalism, speech, and intellect are the most prominent traits that emerged in the evolution of Homo sapiens. Here, we describe a novel genetic cause of an "involution" phenotype in four patients, who are characterized by quadrupedal locomotion, intellectual impairment, the absence of speech, small stature, and hirsutism, observed in a consanguineous Brazilian family. Using whole-genome sequencing analysis and homozygous genetic mapping, we identified genes bearing homozygous genetic variants and found a homozygous 36.2 kb deletion in the gene of glutamate receptor delta 2 (GRID2) in the patients, resulting in the lack of a coding region from the fifth to the seventh exons. The GRID2 gene is highly expressed in the cerebellum cortex from prenatal development to adulthood, specifically in Purkinje neurons. Deletion in this gene leads to the loss of the alpha chain in the extracellular amino-terminal protein domain (ATD), essential in protein folding and transport from the endoplasmic reticulum (ER) to the cell surface. Then, we studied the evolutionary trajectories of the GRID2 gene. There was no sign of strong selection of the highly conservative GRID2 gene in ancient hominids (Neanderthals and Denisovans) or modern humans; however, according to in silico tests using the Mfold tool, the GRID2 gene possibly gained human-specific mutations that increased the stability of GRID2 mRNA.

Genomics of human congenital hydrocephalus

Congenital hydrocephalus (CH), characterized by enlarged brain ventricles, is considered a disease of pathological cerebrospinal fluid (CSF) accumulation and, therefore, treated largely by neurosurgical CSF diversion. The persistence of ventriculomegaly and poor neurodevelopmental outcomes in some post-surgical patients highlights our limited knowledge of disease mechanisms. Recent whole-exome sequencing (WES) studies have shown that rare, damaging de novo and inherited mutations with large effect contribute to ~ 25% of sporadic CH. Interestingly, multiple CH genes are key regulators of neural stem cell growth and differentiation and converge in human transcriptional networks and cell types pertinent to fetal neurogliogenesis. These data implicate genetic disruption of early brain development as the primary pathomechanism in a substantial minority of patients with sporadic CH, shedding new light on human brain development and the pathogenesis of hydrocephalus. These data further suggest WES as a clinical tool with potential to re-classify CH according to a molecular nomenclature of increased precision and utility for genetic counseling, outcome prognostication, and treatment stratification.

Fetal brain arrest broadens the spectrum of WDR81-related developmental brain malformations

Fetal brain arrest is an extremely rare genetic disorder that was described in few patients and encompasses very unique findings of underdeveloped cerebral hemispheres in association with collapsed skull bones. Based on the recurrence among sibs, an autosomal recessive mode of inheritance was proposed; however, no causative gene was identified so far. Here, we report the identification of biallelic variants in the WDR81 gene in two unrelated families (4 patients) with fetal brain arrest including the originally described family and an additional new family. Two homozygous variants were identified: a new missense (c.1157 T > C, p.Val386Ala) and a previously described frameshift variant, c.4668_4669delAG (p.Gly1557AspfsTer16). We assessed the expression of WDR81 at the protein level by western blot analysis using primary skin fibroblast cultures established from the patient with the missense variant and noticed that WDR81 expression was significantly reduced in comparison to normal control confirming the pathogenicity of this variant. Our findings confirm the involvement of WDR81 in the pathogenesis of fetal brain arrest syndrome and suggest that fetal brain arrest represents the severe end of the spectrum phenotypes caused by pathogenic variants in WDR81. In addition, we reviewed the clinical and molecular data on WDR81-related disorders and phenotype/genotype correlations.

Structural Characterization of Carbonic Anhydrase VIII and Effects of Missense Single Nucleotide Variations to Protein Structure and Function

Human carbonic anhydrase 8 (CA-VIII) is an acatalytic isoform of the α -CA family. Though the protein cannot hydrate CO2, CA-VIII is essential for calcium (Ca2+) homeostasis within the body, and achieves this by allosterically inhibiting the binding of inositol 1,4,5-triphosphate (IP3) to the IP3 receptor type 1 (ITPR1) protein. However, the mechanism of interaction of CA-VIII to ITPR1 is not well understood. In addition, functional defects to CA-VIII due to non-synonymous single nucleotide polymorphisms (nsSNVs) result in Ca2+ dysregulation and the development of the phenotypes such as cerebellar ataxia, mental retardation and disequilibrium syndrome 3 (CAMRQ3). The pathogenesis of CAMRQ3 is also not well understood. The structure and function of CA-VIII was characterised, and pathogenesis of CAMRQ3 investigated. Structural and functional characterisation of CA-VIII was conducted through SiteMap and CPORT to identify potential binding site residues. The effects of four pathogenic nsSNVs, S100A, S100P, G162R and R237Q, and two benign S100L and E109D variants on CA-VIII structure and function was then investigated using molecular dynamics (MD) simulations, dynamic cross correlation (DCC) and dynamic residue network (DRN) analysis. SiteMap and CPORT analyses identified 38 unique CA-VIII residues that could potentially bind to ITPR1. MD analysis revealed less conformational sampling within the variant proteins and highlighted potential increases to variant protein rigidity. Dynamic cross correlation (DCC) showed that wild-type (WT) protein residue motion is predominately anti-correlated, with variant proteins showing no correlation to greater residue correlation. DRN revealed variant-associated increases to the accessibility of the N-terminal binding site residues, which could have implications for associations with ITPR1, and further highlighted differences to the mechanism of benign and pathogenic variants. SNV presence is associated with a reduction to the usage of Trp37 in all variants, which has implications for CA-VIII stability. The differences to variant mechanisms can be further investigated to understand pathogenesis of CAMRQ3, enhancing precision medicine-related studies into CA-VIII.

Next-generation sequencing and prenatal 'omics: advanced diagnostics and new insights into human development

Prenatal genetics has evolved over the last decade to include application of new 'omics technologies to improve perinatal care. The clinical utility of these technologies when applied to direct fetal specimens from amniocentesis or chorionic villus sampling is being explored. In this review, we provide an overview of use of prenatal exome sequencing and role in evaluation of the structurally abnormal fetus, potential applications of genome sequencing, and finally, use of transcriptomics to assess placental and fetal well-being.

Nonprogressive congenital ataxias

The terminology of nonprogressive congenital ataxia (NPCA) refers to a clinically and genetically heterogeneous group of disorders characterized by congenital or early-onset ataxia, but no progression or even improvement on follow-up. Ataxia is preceded by muscular hypotonia and delayed motor (and usually language) milestones. We exclude children with prenatal, perinatal, and postnatal acquired diseases, malformations other than cerebellar hypoplasia, and defined syndromic disorders. Patients with NPCA have a high prevalence of cognitive and language impairments, in addition to increased occurrence of seizures, ocular signs (nystagmus, strabismus), behavior changes, and microcephaly. Neuroimaging is variable, ranging from normal cerebellar anatomy to reduced cerebellar volume (hypoplasia in the proper sense), and enlarged interfolial spaces, potentially mimicking atrophy. The latter appearance is often called "hypoplasia" as well, in view of the static clinical course. Some patients had progressive enlargement of cerebellar fissures, but a nonprogressive course. There is no imaging-clinical-genetic correlation. Dominant, recessive, and X-linked inheritance is documented for NPCA. Here, we focus on the still rather short list of dominant and recessive genes associated with NPCA, identified in the last few years. With future advances in genetics, we expect a rapid expansion of knowledge in this field.

Profilin1 biology and its mutation, actin(g) in disease

Profilins were discovered in the 1970s and were extensively studied for their significant physiological roles. Profilin1 is the most prominent isoform and has drawn special attention due to its role in the cytoskeleton, cell signaling, and its link to conditions such as cancer and vascular hypertrophy. Recently, multiple mutations in the profilin1 gene were linked to amyotrophic lateral sclerosis (ALS). In this review, we will discuss the physiological and pathological roles of profilin1. We will further highlight the cytoskeletal function and dysfunction caused by profilin1 dysregulation. Finally, we will discuss the implications of mutant profilin1 in various diseases with an emphasis on its contribution to the pathogenesis of ALS.

Very mild features of dysequilibrium syndrome associated with a novel VLDLR missense mutation

Dysequilibrium syndrome (DES) is a non-progressive congenital ataxia characterized by severe intellectual deficit, truncal ataxia and markedly delayed, quadrupedal or absent ambulation. Recessive loss-of-function mutations in the very low density lipoprotein receptor (VLDLR) gene represent the most common cause of DES. Only two families have been reported harbouring homozygous missense mutations, both with a similarly severe phenotype. We report an Italian girl with very mild DES caused by the novel homozygous VLDLR missense mutation p.(C419Y). This unusually benign phenotype possibly relates to a less disruptive effect of the mutation, falling within a domain (EGF-B) not predicted as crucial for the protein function.

Characterization of a novel zebrafish (Danio rerio) gene, wdr81, associated with cerebellar ataxia, mental retardation and dysequilibrium syndrome (CAMRQ)

Background

WDR81 (WD repeat-containing protein 81) is associated with cerebellar ataxia, mental retardation and disequilibrium syndrome (CAMRQ2, [MIM 610185]). Human and mouse studies suggest that it might be a gene of importance during neurodevelopment. This study aimed at fully characterizing the structure of the wdr81 transcript, detecting the possible transcript variants and revealing its expression profile in zebrafish, a powerful model organism for studying development and disease.

Results

As expected in human and mouse orthologous proteins, zebrafish wdr81 is predicted to possess a BEACH (Beige and Chediak-Higashi) domain, a major facilitator superfamily domain and WD40-repeats, which indicates a conserved function in these species. We observed that zebrafish wdr81 encodes one open reading frame while the transcript has one 5′ untranslated region (UTR) and the prediction of the 3′ UTR was mainly confirmed along with a detected insertion site in the embryo and adult brain. This insertion site was also found in testis, heart, liver, eye, tail and muscle, however, there was no amplicon in kidney, intestine and gills, which might be the result of possible alternative polyadenylation processes among tissues. The 5 and 18 hpf were critical timepoints of development regarding wdr81 expression. Furthermore, the signal of the RNA probe was stronger in the eye and brain at 18 and 48 hpf, then decreased at 72 hpf. Finally, expression of wdr81 was detected in the adult brain and eye tissues, including but not restricted to photoreceptors of the retina, presumptive Purkinje cells and some neurogenic brains regions.

Conclusions

Taken together these data emphasize the importance of this gene during neurodevelopment and a possible role for neuronal proliferation. Our data provide a basis for further studies to fully understand the function of wdr81.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-015-0229-4) contains supplementary material, which is available to authorized users.

Terminology in morphological anomalies of the cerebellum does matter

Neuroimaging plays a key role in the diagnostic work-up of morphological abnormalities of the cerebellum. Diagnostic criteria for numerous morphological anomalies of the cerebellum are based on neuroimaging findings. Various morphological patterns have been described on neuroimaging including cerebellar hypoplasia, cerebellar agenesis, pontocerebellar hypoplasia, cerebellar dysplasia, cerebellar dysmorphia, and cerebellar atrophy. These patterns have specific differential diagnoses. The familiarity with the diagnostic criteria is mandatory for a correct diagnosis and a targeted work-up to avoid unnecessary investigations. A correct diagnosis is essential for early therapy, prognosis, and counseling of the affected children and their family.

Missense mutation in the ATPase, aminophospholipid transporter protein ATP8A2 is associated with cerebellar atrophy and quadrupedal locomotion

Cerebellar ataxia, mental retardation and dysequilibrium syndrome is a rare and heterogeneous condition. We investigated a consanguineous family from Turkey with four affected individuals exhibiting the condition. Homozygosity mapping revealed that several shared homozygous regions, including chromosome 13q12. Targeted next-generation sequencing of an affected individual followed by segregation analysis, population screening and prediction approaches revealed a novel missense variant, p.I376M, in ATP8A2. The mutation lies in a highly conserved C-terminal transmembrane region of E1 E2 ATPase domain. The ATP8A2 gene is mainly expressed in brain and development, in particular cerebellum. Interestingly, an unrelated individual has been identified, in whom mental retardation and severe hypotonia is associated with a de novo t(10;13) balanced translocation resulting with the disruption of ATP8A2. These findings suggest that ATP8A2 is involved in the development of the cerebro-cerebellar structures required for posture and gait in humans.

Role of the actin-binding protein profilin1 in radial migration and glial cell adhesion of granule neurons in the cerebellum

Profilins are small G-actin-binding proteins essential for cytoskeletal dynamics. Of the four mammalian profilin isoforms, profilin1 shows a broad expression pattern, profilin2 is abundant in the brain, and profilin3 and profilin4 are restricted to the testis. In vitro studies on cancer and epithelial cell lines suggested a role for profilins in cell migration and cell-cell adhesion. Genetic studies in mice revealed the importance of profilin1 in neuronal migration, while profilin2 has apparently acquired a specific function in synaptic physiology. We recently reported a mouse mutant line lacking profilin1 in the brain; animals display morphological defects that are typical for impaired neuronal migration. We found that during cerebellar development, profilin1 is specifically required for radial migration and glial cell adhesion of granule neurons. Profilin1 mutants showed cerebellar hypoplasia and aberrant organization of cerebellar cortex layers, with ectopically arranged granule neurons. In this commentary, we briefly introduce the profilin family and summarize the current knowledge on profilin activity in cell migration and adhesion. Employing cerebellar granule cells as a model, we shed some light on the mechanisms by which profilin1 may control radial migration and glial cell adhesion. Finally, a potential implication of profilin1 in human developmental neuropathies is discussed.

Profilin1 is required for glial cell adhesion and radial migration of cerebellar granule neurons

Cerebellar granule neurons (CGNs) exploit Bergmann glia (BG) fibres for radial migration, and cell-cell contacts have a pivotal role in this process. Nevertheless, little is known about the mechanisms that control CGN-BG interaction. Here we demonstrate that the actin-binding protein profilin1 is essential for CGN-glial cell adhesion and radial migration. Profilin1 ablation from mouse brains leads to a cerebellar hypoplasia, aberrant organization of cerebellar cortex layers and ectopic CGNs. Conversely, neuronal progenitor proliferation, tangential migration of neurons and BG morphology appear to be independent of profilin1. Our mouse data and the mapping of developmental neuropathies to the chromosomal region of PFN1 suggest a similar function for profilin1 in humans.

Phenotypical spectrum of cerebellar ataxia associated with a novel mutation in the CA8 gene, encoding carbonic anhydrase (CA) VIII

We define the neurological characteristics of familial cases from multiple branches of a large consanguineous family with cerebellar ataxia, mental retardation (MR), and dysequilibrium syndrome type 3 caused by a mutation in the recently cloned CA8 gene. The linkage analysis revealed a high logarithm of the odds (LOD) score region on 8q that harbors the CA8 in which a novel homozygous c.484G>A (p.G162R) mutation was identified in all seven affected members. The patients had variable cerebellar ataxia and mild cognitive impairment without quadrupedal gait. The brain MRI showed variable cerebellar volume loss and ill-defined peritrigonal white matter abnormalities. The Fluorodeoxyglucose Positron Emission Tomography (FDG PET) revealed hypometabolic cerebellar hemispheres, temporal lobes, and mesial cortex. This report expands the neurological and radiological phenotype associated with CA8 mutations. CA8 involvement should be considered in the differential diagnosis of other genetically unresolved autosomal recessive cerebellar ataxias.

Homozygosity mapping and targeted genomic sequencing reveal the gene responsible for cerebellar hypoplasia and quadrupedal locomotion in a consanguineous kindred

The biological basis for the development of the cerebro-cerebellar structures required for posture and gait in humans is poorly understood. We investigated a large consanguineous family from Turkey exhibiting an extremely rare phenotype associated with quadrupedal locomotion, mental retardation, and cerebro-cerebellar hypoplasia, linked to a 7.1-Mb region of homozygosity on chromosome 17p13.1-13.3. Diffusion weighted imaging and fiber tractography of the patients' brains revealed morphological abnormalities in the cerebellum and corpus callosum, in particular atrophy of superior, middle, and inferior peduncles of the cerebellum. Structural magnetic resonance imaging showed additional morphometric abnormalities in several cortical areas, including the corpus callosum, precentral gyrus, and Brodmann areas BA6, BA44, and BA45. Targeted sequencing of the entire homozygous region in three affected individuals and two obligate carriers uncovered a private missense mutation, WDR81 p.P856L, which cosegregated with the condition in the extended family. The mutation lies in a highly conserved region of WDR81, flanked by an N-terminal BEACH domain and C-terminal WD40 beta-propeller domains. WDR81 is predicted to be a transmembrane protein. It is highly expressed in the cerebellum and corpus callosum, in particular in the Purkinje cell layer of the cerebellum. WDR81 represents the third gene, after VLDLR and CA8, implicated in quadrupedal locomotion in humans.

Uner tan syndrome: history, clinical evaluations, genetics, and the dynamics of human quadrupedalism

This review includes for the first time a dynamical systems analysis of human quadrupedalism in Uner Tan syndrome, which is characterized by habitual quadrupedalism, impaired intelligence, and rudimentary speech. The first family was discovered in a small village near Iskenderun, and families were later found in Adana and two other small villages near Gaziantep and Canakkale. In all the affected individuals dynamic balance was impaired during upright walking, and they habitually preferred walking on all four extremities. MRI scans showed inferior cerebellovermian hypoplasia with slightly simplified cerebral gyri in three of the families, but appeared normal in the fourth. PET scans showed a decreased glucose metabolic activity in the cerebellum, vermis and, to a lesser extent the cerebral cortex, except for one patient, whose MRI scan also appeared to be normal. All four families had consanguineous marriages in their pedigrees, suggesting autosomal recessive transmission. The syndrome was genetically heterogeneous. Since the initial discoveries more cases have been found, and these exhibit facultative quadrupedal locomotion, and in one case, late childhood onset. It has been suggested that the human quadrupedalism may, at least, be a phenotypic example of reverse evolution. From the viewpoint of dynamic systems theory, it was concluded there may not be a single factor that predetermines human quadrupedalism in Uner Tan syndrome, but that it may involve self-organization, brain plasticity, and rewiring, from the many decentralized and local interactions among neuronal, genetic, and environmental subsystems.

Novel VLDLR microdeletion identified in two Turkish siblings with pachygyria and pontocerebellar atrophy

Congenital ataxia with cerebellar hypoplasia is a heterogeneous group of disorders that presents with motor disability, hypotonia, incoordination, and impaired motor development. Among these, disequilibrium syndrome describes a constellation of findings including non-progressive cerebellar ataxia, mental retardation, and cerebellar hypoplasia following an autosomal recessive pattern of inheritance and can be caused by mutations in the Very Low Density Lipoprotein Receptor (VLDLR). Interestingly, while the majority of patients with VLDL-associated cerebellar hypoplasia in the literature use bipedal gait, the previously reported patients of Turkish decent have demonstrated similar neurological sequelae, but rely on quadrupedal gait. We present a consanguinous Turkish family with two siblings with cerebellar atrophy, predominantly frontal pachygyria and ataxic bipedal gait, who were found to have a novel homozygous deletion in the VLDLR gene identified by using high-density single nucleotide polymorphism microarrays for homozygosity mapping and identification of CNVs within these regions. Discovery of disease causing homozygous deletions in the present Turkish family capable of maintaining bipedal movement exemplifies the phenotypic heterogeneity of VLDLR-associated cerebellar hypoplasia and ataxia.

Mutations in VLDLR as a cause for autosomal recessive cerebellar ataxia with mental retardation (dysequilibrium syndrome)

Dysequilibrium syndrome is a genetically heterogeneous condition that combines autosomal recessive, nonprogressive cerebellar ataxia with mental retardation. Here, we report the first patient heterozygous for 2 novel mutations in VLDLR. An 18-month-old girl presented with significant hypotonia, global developmental delay, and truncal and peripheral ataxia. Magnetic resonance imaging of the brain demonstrated hypoplasia of the inferior cerebellar vermis and hemispheres, small pons, and a simplified cortical sulcation pattern. Sequence analysis of the VLDLR gene identified a nonsense and missense mutation. Six mutations in VLDLR have now been identified in 5 families with a phenotype characterized by moderate-to-profound mental retardation, delayed ambulation, truncal and peripheral ataxia, and occasional seizures. Neuroanatomically, the loss-of-function effect of the different mutations is indistinguishable. VLDLR-associated cerebellar hypoplasia is emerging as a panethnic, clinically, and molecularly well-defined genetic syndrome.

Morphological spectrum of prenatal cerebellar disruptions

There is increasing evidence that the cerebellum is susceptible to both prenatal infections and haemorrhages as well as being vulnerable in extremely preterm babies, but not to perinatal and postnatal hypoxic-ischaemic injuries. Starting with the imaging appearance we describe and illustrate a spectrum of prenatal cerebellar disruptions: cerebellar agenesis; unilateral cerebellar hypoplasia; unilateral cerebellar cleft; global cerebellar hypoplasia; vanishing cerebellum in myelomeningocele; and disruption of cerebellar development in preterm infants. We discuss neuroradiological characteristics, possible disruptive events, and clinical findings in the different morphological patterns. Remarkably, the same disruptive agent can cause different neuroradiological patterns, which appear likely to represent a morphological spectrum. The analysis of imaging patterns is crucial in recognising cerebellar disruptions. Recognition of cerebellar disruptions and their differentiation from cerebellar malformations is important in terms of diagnosis, prognosis, and genetic counselling.

A WRIST-WALKER EXHIBITING NO “UNER TAN SYDNROME”: A THEORY FOR POSSIBLE MECHANISMS OF HUMAN DEVOLUTION TOWARD THE ATAVISTIC WALKING PATTERNS

After discovering two families with handicapped children exhibiting the "Uner Tan syndrome," the author discovered a man exhibiting only wrist-walking with no primitive mental abilities including language. According to his mother, he had an infectious disease with high fever as a three months old baby; as a result, the left leg had been paralyzed after a penicilline injection. This paralysis most probably resulted from a viral disease, possibly poliomyelitis. He is now (2006) 36 years old; the left leg is flaccid and atrophic, with no tendon reflexes; however, sensation is normal. The boy never stood up on his feet while maturing. The father forced him to walk upright using physical devices and making due exercises, but the child always rejected standing upright and walking in erect posture; he always preferred wrist-walking; he expresses that wrist-walking is much more comfortable for him than upright-walking. He is very strong now, making daily body building exercises, and walking quite fast using a "three legs," although he cannot stand upright. Mental status, including the language and conscious experience, is quite normal. There was no intra-familiar marriage as in the two families mentioned earlier, and there is no wrist-walking in his family and relatives. There were no cerebellar signs and symptoms upon neurological examination. The brain-MRI was normal; there was no atrophy in cerebellum and vermis. It was concluded that there may be sporadic wrist-walkers exhibiting no "Uner Tan Syndrome." The results suggest that the cerebellum has nothing to do with human wrist-walking, which may rather be an atavistic trait appearing from time to time in normal individuals, indicating a live model for human reverse evolution. It was concluded that pure quadrupeds may sporadically appear due to random fluctuations in genotypes and/or environmental factors (hormonal or nutritional); the human development following the human evolution may be stopped in the stage of transition from quadrupedality to bipedality. That is, the activity of the philogenetically youngest supraspinal centers for bipedal walking responsible for suppression of the older supraspinal centers for quadrupedal gait may be interrupted at the atavistic level due to genetic and/or environmental factors. Consequently, it is assumed that these individuals prefer their natural wrist-walking to move around more quickly and efficiently.

CA8 mutations cause a novel syndrome characterized by ataxia and mild mental retardation with predisposition to quadrupedal gait

We describe a consanguineous Iraqi family in which affected siblings had mild mental retardation and congenital ataxia characterized by quadrupedal gait. Genome-wide linkage analysis identified a 5.8 Mb interval on chromosome 8q with shared homozygosity among the affected persons. Sequencing of genes contained in the interval revealed a homozygous mutation, S100P, in carbonic anhydrase related protein 8 (CA8), which is highly expressed in cerebellar Purkinje cells and influences inositol triphosphate (ITP) binding to its receptor ITPR1 on the endoplasmatic reticulum and thereby modulates calcium signaling. We demonstrate that the mutation S100P is associated with proteasome-mediated degradation, and thus presumably represents a null mutation comparable to the Ca8 mutation underlying the previously described waddles mouse, which exhibits ataxia and appendicular dystonia. CA8 thus represents the third locus that has been associated with quadrupedal gait in humans, in addition to the VLDLR locus and a locus at chromosome 17p. Our findings underline the importance of ITP-mediated signaling in cerebellar function and provide suggestive evidence that congenital ataxia paired with cerebral dysfunction may, together with unknown contextual factors during development, predispose to quadrupedal gait in humans.

We identified a homozygous missense mutation (S100P) in the gene encoding carbonic anhydrase VIII in a consanguineous Iraqi family in which affected siblings had mild mental retardation and congenital ataxia characterized by quadrupedal gait. The affected persons walk on their hands and feet with their legs held straight with a “bear-like” gait. Our results show that the mutation S100P induces proteasome-mediated degradation with a severe reduction of the level of CA8 protein. The waddles (wdl) mouse, a spontaneous animal model with ataxia, was previously shown to harbor a 19-bp deletion in Ca8 that leads to an almost complete lack of detectable Ca8 protein, resulting in abnormalities in cerebellar synaptic transmission. Therefore, we speculate that the reduction in CA8 protein concentration associated with the S100P mutation could result in similar pathophysiological effects. With the current report, alterations at three gene loci (CA8, VLDLR, and a yet-to-be discovered gene on chromosome 17p) have been reported to be associated with quadrupedal gait. It is unknown whether quadrupedal gait is related to specific molecular abnormalities or is an adaptive response to ataxia in some circumstances. However, we note that ataxia associated with mutations at all three loci is congenital and also associated with mental retardation, which is not generally a feature of other hereditary ataxias.

In restless legs syndrome, the neural substrates of the sensorimotor symptoms are also normally involved in upright standing posture and biped walking

Restless legs syndrome (RLS) exhibits sensorimotor symptoms. In familial cases, a gene at chromosomal location 9p-24-22 is linked to RLS and the expressed mutation is Dopamine Receptor Specific Individual Sensitivity (DRSIS). The symptoms are triggered during changes in alertness, generally at sleep hours, resulting from insufficient dopamine transmission. The conscious experience of sensory abnormalities are described as 'an urge to move the limbs with or without paresthesias' leading to motor signs such as periodic limb movements and motor restlessness which exhibit temporary loss of extensor motor system dominance over the flexor motor system of the upright posture. The relationship of the expressed mutation to EEG alpha activity makes RLS a sleep disorder as well as a cognitive dysfunction. The recurrent character of sensorimotor symptoms impede the patient's ability to sleep, wake and force to move leading to insomnia. In Uner Tan Syndrome, the nonsense mutation in the same gene leads to underdevelopment of the neural substrates of upright posture. The defects include dopamine receptor deficiency (DRD) leading to severe cognitive dysfunctions and motor disorders-complete loss of extensor motor system dominance over the flexor motor system-quadrupedality, primitive speech, cerebellar symptoms, and strabismus. Comparisons between the neural substrates of sensorimotor symptoms seen in RLS and MRI findings for cases of Uner Tan Syndrome show cortico-cerebellar hypoplasias in the neural networks involved in upright posture. Both RLS and Uner Tan Syndrome seem to be due to different mutations in the dopamine receptor gene at 9p-24 locus, affecting the diencephalon dopaminergic system and the neural networks involved in upright posture.

"Unertan syndrome" in two Turkish families in relation to devolution and emergence of Homo erectus: neurological examination, MRI, and PET scans

"Unertan syndrome" consists of two main symptoms: quadrupedal gait and primitive cognitive abilities including language and conscious experience. To assess the central mechanisms involved in this syndrome, the authors performed MRI and PET scans on affected and unaffected individuals from both families. All affected individuals were also subjected to neurological examination. To assess the integrity of the peripheral and central vestibular system, Barany's caloric test was applied to the affected individuals. Brain MRI and PET scans were performed on normal subjects (n = 7) and patients (n = 7). Right- and left-cerebral and cerebellar areas, including the vermial and callosal areas, were measured on the MRI scans using a computer cursor. Quadrupedal gait, mental retardation, dysartric speech, nystagmus, severe truncal ataxia, hyperreflexia, astasia, and abasia were observed in the affected individuals from both families. Cerebellum and vermis were atrophic in the MRI and PET scans of the first family. In contrast, the brain MRI seemed to be normal in the MRI and PET scans of affected individuals from the second family. The caloric test revealed central vestibular damage in patients from the first family and peripheral vestibular damage in patients from the second family. The results suggest that "Unertan syndrome," discovered in two unrelated families, may be caused by peripheral or central vestibular damage resulting from different genetic defects. Cerebellar hypoplasia may not be a prerequisite for the emergence of this syndrome. Primitive mental abilities may be explained by damage within the vestibulo-cerebellar system, whereas the quadrupedal gait may be due to a genetic defect within the higher brain centers that suppress the atavistic brain networks controlling quadrupedal gait and helped in the emergence of the habitual bipedal gait during human evolution. This retarded development of human locomotion - devolution - may illuminate the brain mechanisms responsible for the transition from quadrupedality to bipedality in human evolution.

Differential diagnosis of cerebellar atrophy in childhood

Starting from the imaging appearance of cerebellar atrophy (CA) we provide checklists for various groups of CA: hereditary CA, postnatally acquired CA, and unilateral CA. We also include a list of disorders with ataxia as symptom, but no evidence of CA on imaging. These checklists may be helpful in the evaluation of differential diagnosis and planning of additional investigations. However, the complete constellation of clinical (including history and neurological examination), imaging, and other information have to be considered. On the basis of a single study distinction between prenatal onset atrophy, postnatal onset atrophy, and cerebellar hypoplasia is not always possible. Apart from rare exceptions, neuroimaging findings of CA are nonspecific. A pattern-recognition approach is suggested, considering isolated (pure) CA, CA and hypomyelination, CA and progressive white matter abnormalities, CA and basal ganglia involvement, and cerebellar cortex hyperintensity.

Unertan syndrome: review and report of four new cases

The aim of this study was to describe additional patients (n= 3) exhibiting the Unertan syndrome (UTS), resident in rural areas of Canakkale. The 8th and 9th families with the UTS, with a total of 16 members affected, have not been previously characterized. A single, non-familial case (Bayramic, Canakkale) occurred during early childhood after an infection with a high fever. Three cases of familial UTS were located in another village in Canakkale. All cases exhibited the three key symptoms of the UTS: (1) walking on all four extremities, (2) primitive language (only sounds), and (3) rudimentary intelligence. Magnetic resonance imaging showed mild vermial hypoplasia in the non-familial case, while there was cerebellar and vermial hypoplasia with a flattened cerebral cortex in the familial cases. Dexterity of the fingers was normal. The man from the latter family was fond of dragging a wooden box after fastening a string around his belt. The collective observations and clinical findings suggest two etiologies for the UTS: (1) genetic, via autosomal recessive transmission and (2) viral, likely the poliovirus affecting the cerebro-cerebellar structures. At a minimum, vermial hypoplasia is suggested to cause fully developed UTS. The subjects could stand upright and even walk bipedally, despite difficulties in balance (ataxia), but they preferred quadrupedal walking. The main difficulty with gait was maintaining a dynamic-asymmetric lateral balance and initiation of the first step during standing. Apparently, a quadrupedal gait in an adult is a developmental regression with absence of the higher control mechanisms for asymmetric lateral balance during bipedal walking. It is suggested that these individuals exhibit ancestral traits; the quadrupedal gait with rudimentary intelligence and primitive speech resulting from viral infections and/or genetic damage may cause devolution (reverse evolution), a manifestation of an experiment of nature as well as experimental studies in animal models. The results support the notion of punctuated evolution, in contrast to Darwin's theory of graded evolution. Dragging a wooden box using a string wrapped around the belt may also be an example of reverse evolution with regard to tool making, illuminating the very long-lasting period before the invention of the wheel. Herein, there has been no intent to insult or injure these individuals affected by the UTS; rather, this is an endeavor to better understand the mystery of human evolution. Go to the publisher's online edition of International Journal of Neuroscience for the following free supplemental resource: video clips.

Cerebellar hypoplasia, with quadrupedal locomotion, caused by mutations in the very low-density lipoprotein receptor gene

The cerebellum is the primary motor coordination centre of the central nervous system. Lesions or congenital defects of the cerebellum cause incoordination of the muscles resulting in irregular gait and falling. Recently, we reported a large family with cerebellum hypoplasia and quadrupedal locomotion as a recessive trait, which we mapped to chromosome 17p13. We identified one additional family with the same condition and mapped the underlying gene to a 14-cM interval on chromosome 9ptel using a genome-wide linkage approach. Sequencing of candidate genes identified a homozygous frameshift mutation in the very low-density lipoprotein receptor (VLDLR) gene in all affected individuals. The association of cerebellar hypoplasia with mutations in VLDLR has been reported previously in the Hutterite population and in a family from Iran. However, quadrupedal locomotion was never observed indicating that environmental factors play a major role in the pathogenesis of this form of locomotion.

Unertan syndrome: a case series demonstrating human devolution

A large family with six individuals exhibiting the Unertan syndrome (UTS) was identified residing in southern Turkey. All of the individuals had mental impairments and walked on all four extremities. The practice of intra-familial marriages suggested that the UTS may be an autosomal recessive disorder, similar to previously described cases. The inferior portions of the cerebellum and vermis were absent as evidenced by MRI and CT scans. The height and head circumference of those affected were within normal ranges. Barany's test suggested normal vestibular system function. The subjects could not name objects or their close relatives. The males (n = 4) could understand simple questions and commands, but answered questions with only one or two sounds. The females (n = 2) were superior to the males with respect to language skills and walking, suggesting an association between walking and speaking abilities. One male exhibited three walking patterns at the same time: quadripedal, tiptoe, and scissor walking. Another male used two walking styles: quadripedal and toe-walking. It is emphasized that there are important differences between the UTS and the disequilibrium syndrome. It is suggested that the inability to walk upright in those affected with the UTS may be best explained by a disturbance in lateral-balance mechanisms, without being related to the cerebello-vestibular system. An interruption of locomotor development during the transition from quadripedality to bipedality may result in habitual walking on all four extremities and is normal in some children. Because quadripedal gait is an ancestral trait, individuals with the UTS, exhibiting a manifestation of reverse evolution in humans, may be considered an experiment of nature, useful in understanding the mechanisms underlying the transition from quadripedality to bipedality during human evolution. The proposed mutant gene or gene pool playing a role in human quadrupedality may also be responsible for human bipedality at the same time. Herein there is no intent to insult or injure; rather, this report is an endeavor to better understand human beings. Supplementary materials are available for this article. Go to the publisher's online edition of International Journal of Neuroscience for the following free supplemental resource(s): video clips.

Mutations in the very low-density lipoprotein receptor VLDLR cause cerebellar hypoplasia and quadrupedal locomotion in humans

Quadrupedal gait in humans, also known as Unertan syndrome, is a rare phenotype associated with dysarthric speech, mental retardation, and varying degrees of cerebrocerebellar hypoplasia. Four large consanguineous kindreds from Turkey manifest this phenotype. In two families (A and D), shared homozygosity among affected relatives mapped the trait to a 1.3-Mb region of chromosome 9p24. This genomic region includes the VLDLR gene, which encodes the very low-density lipoprotein receptor, a component of the reelin signaling pathway involved in neuroblast migration in the cerebral cortex and cerebellum. Sequence analysis of VLDLR revealed nonsense mutation R257X in family A and single-nucleotide deletion c2339delT in family D. Both these mutations are predicted to lead to truncated proteins lacking transmembrane and signaling domains. In two other families (B and C), the phenotype is not linked to chromosome 9p. Our data indicate that mutations in VLDLR impair cerebrocerebellar function, conferring in these families a dramatic influence on gait, and that hereditary disorders associated with quadrupedal gait in humans are genetically heterogeneous.

Human balance, the evolution of bipedalism and dysequilibrium syndrome

A new model of the uniqueness, nature and evolution of human bipedality is presented in the context of the etiology of the balance disorder of dysequilibrium syndrome. Human bipedality is biologically novel in several remarkable respects. Humans are (a) obligate, habitual and diverse in their bipedalism, (b) hold their body carriage spinally erect in a multisegmental "antigravity pole", (c) use their forelimbs exclusively for nonlocomotion, (d) support their body weight exclusively by vertical balance and normally never use prehensile holds. Further, human bipedalism is combined with (e) upper body actions that quickly shift the body's center of mass (e.g. tennis serves, piggy-back carrying of children), (f) use transient unstable erect positions (dance, kicking and fighting), (g) body height that makes falls injurious, (h) stiff gait walking, and (i) endurance running. Underlying these novelties, I conjecture, is a species specific human vertical balance faculty. This faculty synchronizes any action with a skeletomuscular adjustment that corrects its potential destabilizing impact upon the projection of the body's center of mass over its foot support. The balance faculty depends upon internal models of the erect vertical body's geometrical relationship (and its deviations) to its support base. Due to the situation that humans are obligate erect terrestrial animals, two frameworks - the body- and gravity-defined frameworks - are in constant alignment in the vertical z-axis. This alignment allows human balance to adapt egocentric body cognitions to detect body deviations from the gravitational vertical. This link between human balance and the processing of geometrical orientation, I propose, accounts for the close link between balance and spatial cognition found in the cerebral cortex. I argue that cortical areas processing the spatial and other cognitions needed to enable vertical balance was an important reason for brain size expansion of Homo erectus. A novel source of evidence for this conjecture is the rare autosomal recessive condition of dysequilibrium syndrome. In dysequilibrium syndrome, individuals fail to learn to walk bipedally (with this not being due to sensory, vestibular nor motor coordination defects). Dysequilibrium syndrome is associated with severe spatial deficits that I conjecture underlie its balance dysfunction. The associated brain defects and gene mutations of dysequilibrium syndrome provide new opportunities to investigate (i) the neurological processes responsible for the human specific balance faculty, and (ii) through gene dating techniques, its evolution.