Cataracts, motor system disorder, short stature, learning difficulties, and skeletal abnormalities: a new syndrome?

The hereditary spastic paraplegias

The hereditary spastic paraplegias (HSPs) are a group of more than 90 genetic disorders in which lower extremity spasticity and weakness are either the primary neurologic impairments ("uncomplicated HSP") or when accompanied by other neurologic deficits ("complicated HSP"), important features of the clinical syndrome. Various genetic types of HSP are inherited such as autosomal dominant, autosomal recessive, X-linked, and maternal (mitochondrial) traits. Symptoms that begin in early childhood may be nonprogressive and resemble spastic diplegic cerebral palsy. Symptoms that begin later, typically progress insidiously over a number of years. Genetic testing is able to confirm the diagnosis for many subjects. Insights from gene discovery indicate that abnormalities in diverse molecular processes underlie various forms of HSP, including disturbance in axon transport, endoplasmic reticulum morphogenesis, vesicle transport, lipid metabolism, and mitochondrial function. Pathologic studies in "uncomplicated" HSP have shown axon degeneration particularly involving the distal ends of corticospinal tracts and dorsal column fibers. Treatment is limited to symptom reduction including amelioration of spasticity, reducing urinary urgency, proactive physical therapy including strengthening, stretching, balance, and agility exercise.

Two novel mutations in ALDH18A1 and SPG11 gene found by whole-exome sequencing in spastic paraplegia disease patients in Iran

Hereditary spastic paraplegia is a not common inherited neurological disorder with heterogeneous clinical expressions. ALDH18A1 (located on 10q24.1) gene-related spastic paraplegias (SPG9A and SPG9B) are rare metabolic disorders caused by dominant and recessive mutations that have been found recently. Autosomal recessive hereditary spastic paraplegia is a common and clinical type of familial spastic paraplegia linked to the SPG11 locus (locates on 15q21.1). There are different symptoms of spastic paraplegia, such as muscle atrophy, moderate mental retardation, short stature, balance problem, and lower limb weakness. Our first proband involves a 45 years old man and our second proband involves a 20 years old woman both are affected by spastic paraplegia disease. Genomic DNA was extracted from the peripheral blood of the patients, their parents, and their siblings using a filter-based methodology and quantified and used for molecular analysis and sequencing. Sequencing libraries were generated using Agilent SureSelect Human All ExonV7 kit, and the qualified libraries are fed into NovaSeq 6000 Illumina sequencers. Sanger sequencing was performed by an ABI prism 3730 sequencer. Here, for the first time, we report two cases, the first one which contains likely pathogenic NM_002860: c.475C>T: p.R159X mutation of the ALDH18A1 and the second one has likely pathogenic NM_001160227.2: c.5454dupA: p.Glu1819Argfs Ter11 mutation of the SPG11 gene and also was identified by the whole-exome sequencing and confirmed by Sanger sequencing. Our aim with this study was to confirm that these two novel variants are direct causes of spastic paraplegia.

The Multifaceted Roles of Proline in Cell Behavior

Herein, we review the multifaceted roles of proline in cell biology. This peculiar cyclic imino acid is: (i) A main precursor of extracellular collagens (the most abundant human proteins), antimicrobial peptides (involved in innate immunity), salivary proteins (astringency, teeth health) and cornifins (skin permeability); (ii) an energy source for pathogenic bacteria, protozoan parasites, and metastatic cancer cells, which engage in extracellular-protein degradation to invade their host; (iii) an antistress molecule (an osmolyte and chemical chaperone) helpful against various potential harms (UV radiation, drought/salinity, heavy metals, reactive oxygen species); (iv) a neural metabotoxin associated with schizophrenia; (v) a modulator of cell signaling pathways such as the amino acid stress response and extracellular signal-related kinase pathway; (vi) an epigenetic modifier able to promote DNA and histone hypermethylation; (vii) an inducer of proliferation of stem and tumor cells; and (viii) a modulator of cell morphology and migration/invasiveness. We highlight how proline metabolism impacts beneficial tissue regeneration, but also contributes to the progression of devastating pathologies such as fibrosis and metastatic cancer.

[Autosomal dominant spastic paraplegias]

OBJECTIVE

To estimate the proportion and spectrum of infrequent autosomal dominant spastic paraplegias in a group of families with DNA-confirmed diagnosis and to investigate their molecular and clinical characteristics.

MATERIAL AND METHODS

Ten families with 6 AD-SPG: SPG6 (n=1), SPG8 (n=2), SPG9A (n=1), SPG12 (n=1), SPG17 (n=3), SPG31 (n=2) were studied using clinical, genealogical, molecular-genetic (massive parallel sequencing, spastic paraplegia panel, whole-exome sequencing, multiplex ligation-dependent amplification, Sanger sequencing) and bioinformatic methods.

RESULTS AND CONCLUSION

Nine heterozygous mutations were detected in 6 genes, including the common de novo mutation p.Gly106Arg in NIPA1 (SPG6), the earlier reported mutation p.Val626Phe in WASHC5 (SPG8) in isolated case and the novel p.Val695Ala in WASHC5 (SPG8) in a family with 4 patients, the novel mutation p.Thr301Arg in RTN2 (SPG12) in a family with 2 patients, the novel mutation c.105+4A>G in REEP1 (SPG31) in a family with 4 patients and the reported earlier p.Lys101Lys in REEP1 (SPG31) in a family with 3 patients, the known de novo mutation p.Arg252Gln in ALDH18A1 (SPG9A) in two monozygous twins; the common mutation p.Ser90Leu in BSCL2 (SPG17) in a family with 3 patients and in isolated case, reported mutation p.Leu363Pro in a family with 2 patients. SPG6, SPG8, SPG12 and SPG31 presented 'pure' phenotypes, SPG31 had most benign course. Age of onset varied in SPG31 family and was atypically early in SPG6 case. Patients with SPG9A and SPG17 had 'complicated' paraplegias; amyotrophy of hands typical for SPG17 was absent in a child and in an adolescent from 2 families, but may develop later.

SPG9A with the new occurrence of an ALDH18A1 mutation in a CMT1A family with PMP22 duplication: case report

Background

ALDH18A1 mutations lead to delta-1-pyrroline-5-carboxylate-synthetase (P5CS) deficiency, which is a urea cycle-related disorder including SPG9A, SPG9B, autosomal dominant cutis laxa-3 (ADCL3), and autosomal recessive cutis laxa type 3A (ARCL3A). These diseases exhibit a broad clinical spectrum, which makes the diagnosis of P5CS deficiency difficult. We report here a rare Japanese family including both patients with an ALDH18A1 mutation (SPG9A) and ones with CMT1A.

Case presentation

A Japanese family included five patients with the CMT phenotype and five with the HSP phenotype in four generations. The patients with the HSP phenotype showed a pure or complicated form, and intrafamilial clinical variability was noted. Genetically, FISH analysis revealed that two CMT patients had a PMP22 duplication (CMT1A). Exome analysis and Sanger sequencing revealed five HSP patients had an ALDH18A1 heterozygous mutation of c.755G > A, which led to SPG9A. Haplotype analysis revealed that the ALDH18A1 mutation must have newly occurred. To date, although de novo mutations of ALDH18A1 have been described in ADCL3A, they were not mentioned in SPG9A in earlier reports. Thus, this is the first SPG9A family with a de novo mutation or the new occurrence of gonadal mosaicism of ALDH18A1. Analysis of serum amino acid levels revealed that two SPG9A patients and two unaffected family members had low citrulline levels and one had a low level of ornithine.

Conclusions

Since the newly occurring ALDH18A1 mutation, c.755G > A, is the same as that in two ADHSP families and one sporadic patient with SPG9A reported previously, this genomic site might easily undergo mutation. The patients with the c.755G > A mutation in our family showed clinical variability of symptoms like in the earlier reported two families and one sporadic patient with this mutation. Further studies are required to clarify the relationship between the amino acid levels and clinical manifestations, which will reveal how P5CS deficiency influences disease phenotypes including ARCL3A, ADCL3, SPG9B, and SPG9A.

Δ1 -Pyrroline-5-carboxylate synthetase deficiency: An emergent multifaceted urea cycle-related disorder

The bifunctional homooligomeric enzyme Δ¹ -pyrroline-5-carboxylate synthetase (P5CS) and its encoding gene ALDH18A1 were associated with disease in 1998. Two siblings who presented paradoxical hyperammonemia (alleviated by protein), mental disability, short stature, cataracts, cutis laxa, and joint laxity, were found to carry biallelic ALDH18A1 mutations. They showed biochemical indications of decreased ornithine/proline synthesis, agreeing with the role of P5CS in the biosynthesis of these amino acids. Of 32 patients reported with this neurocutaneous syndrome, 21 familial ones hosted homozygous or compound heterozygous ALDH18A1 mutations, while 11 sporadic ones carried de novo heterozygous ALDH18A1 mutations. In 2015 to 2016, an upper motor neuron syndrome (spastic paraparesis/paraplegia SPG9) complicated with some traits of the neurocutaneous syndrome, although without report of cutis laxa, joint laxity, or herniae, was associated with monoallelic or biallelic ALDH18A1 mutations with, respectively, dominant and recessive inheritance. Of 50 SPG9 patients reported, 14 and 36 (34/2 familial/sporadic) carried, respectively, biallelic and monoallelic mutations. Thus, two neurocutaneous syndromes (recessive and dominant cutis laxa 3, abbreviated ARCL3A and ADCL3, respectively) and two SPG9 syndromes (recessive SPG9B and dominant SPG9A) are caused by essentially different spectra of ALDH18A1 mutations. On the bases of the clinical data (including our own prior patients' reports), the ALDH18A1 mutations spectra, and our knowledge on the P5CS protein, we conclude that the four syndromes share the same pathogenic mechanisms based on decreased P5CS function. Thus, these syndromes represent a continuum of increasing severity (SPG9A < SPG9B < ADCL3 ≤ ARCL3A) of the same disease, P5CS deficiency, in which the dominant mutations cause loss-of-function by dominant-negative mechanisms.

Autosomal dominant SPG9: intrafamilial variability and onset during pregnancy

INTRODUCTION

The ALDH18A1 gene, encoding delta-1-pyrroline-5-carboxylate synthase (P5CS), is responsible for an autosomal recessive disease with severe developmental delay; more recently, ALDH18A1 was found to be responsible for SPG9, an autosomal dominant (AD) spastic paraplegia.

CASE REPORT

We report a three-generation family with AD SPG9, initially suspected because of low citrulline on fasting plasma amino acid chromatography (AAC). Interestingly, in two patients, the spastic paraplegia appeared during pregnancy. One subject presented a severe childhood-onset form while another subject had a mild late-onset disease.

CONCLUSION

The description of this family is of particular interest: it highlights the possibility of transient or permanent aggravation of spastic paraplegia due to SPG9 during pregnancy, suggesting a direct link between neurological symptoms and amino acid defect in a period of higher requirements and the potential benefit of amino acid supplementation; it underscores the value of plasma citrulline on fasting plasma AAC as a biomarker for this disease; it shows the variable expression of the disease.

Complexity of Generating Mouse Models to Study the Upper Motor Neurons: Let Us Shift Focus from Mice to Neurons

Motor neuron circuitry is one of the most elaborate circuitries in our body, which ensures voluntary and skilled movement that requires cognitive input. Therefore, both the cortex and the spinal cord are involved. The cortex has special importance for motor neuron diseases, in which initiation and modulation of voluntary movement is affected. Amyotrophic lateral sclerosis (ALS) is defined by the progressive degeneration of both the upper and lower motor neurons, whereas hereditary spastic paraplegia (HSP) and primary lateral sclerosis (PLS) are characterized mainly by the loss of upper motor neurons. In an effort to reveal the cellular and molecular basis of neuronal degeneration, numerous model systems are generated, and mouse models are no exception. However, there are many different levels of complexities that need to be considered when developing mouse models. Here, we focus our attention to the upper motor neurons, which are one of the most challenging neuron populations to study. Since mice and human differ greatly at a species level, but the cells/neurons in mice and human share many common aspects of cell biology, we offer a solution by focusing our attention to the affected neurons to reveal the complexities of diseases at a cellular level and to improve translational efforts.

A new phenotype linked to SPG27 and refinement of the critical region on chromosome

Hereditary spastic paraplegias are genetically and clinically heterogeneous. Twenty-six loci have been identified to date. SPG27 was recently mapped to chromosome 10 in a single family with autosomal recessive hereditary spastic paraplegia (AR-HSP) and a pure phenotype. We describe a Tunisian family with a complicated form of AR-HSP also linked to SPG27. The parents are first cousins and 3 out of their 4 children manifest early onset progressive spastic paraparesis associated with sensorimotor polyneuropathy. In addition, the eldest girl had facial dysmorphism and short stature (-3SD). Two of the three patients were mentally retarded, and one of these also had cerebellar signs. Their ages at onset were 2, 5 and 7 years. A genome-wide scan suggested linkage to SPG27 on the long arm of chromosome 10 with a multipoint lod score of 2.54. In addition, a recombination detected in this family by haplotype reconstruction reduced the SPG27 locus from 25 to 19.6 cM. This is the first clinical description of a complicated form of spastic paraplegia, characterized by great phenotypic variability among the sibs, associated with the SPG27 locus.

A novel locus for pure recessive hereditary spastic paraplegia maps to 10q22.1-10q24.1

The hereditary spastic paraplegias (HSPs) are a group of clinically and genetically heterogeneous disorders characterized by progressive lower-limb spasticity. In this study, we performed linkage analysis on an autosomal recessive pure HSP family and mapped the disease to chromosome 10q22.1-10q24.1, a locus partially overlapping the existing SPG9 locus. We have either identified a novel locus for pure recessive HSP (SPG27), or we have found the first case of allelic disorders with different mode of inheritance in HSP. If the disorders are indeed allelic, our results have reduced the SPG9 interval by 3Mb with D10S536 and D10S1758 as flanking markers.

Genetic mapping to 10q23.3-q24.2, in a large Italian pedigree, of a new syndrome showing bilateral cataracts, gastroesophageal reflux, and spastic paraparesis with amyotrophy

We have recently observed a large pedigree with a new rare autosomal dominant spastic paraparesis. In three subsequent generations, 13 affected individuals presented with bilateral cataracts, gastroesophageal reflux with persistent vomiting, and spastic paraparesis with amyotrophy. Bilateral cataracts occurred in all affected individuals, with the exception of one patient who presented with a chorioretinal dystrophy, whereas clinical signs of spastic paraparesis showed a variable expressivity. Using a genomewide mapping approach, we mapped the disorder to the long arm of chromosome 10 on band q23.3-q24.2, in a 12-cM chromosomal region where additional neurologic disorders have been localized. The spectrum of phenotypic manifestations in this family is reminiscent of a smaller pedigree, reported recently, confirming the possibility of a new syndrome. Finally, the anticipation of symptoms suggests that an unstable trinucleotide repeat may be responsible for the condition.