Infantile demyelinating neuropathy associated with a de novo point mutation on Ser72 in PMP22 and basal lamina onion bulbs in skin biopsy

A case report of two Moroccan patients with hereditary neurological disorders and molecular modeling study on the S72L de novo PMP22 variant

Hereditary neurological disorders represent a wild group of hereditary illnesses affecting mainly the nervous system, the majority of which have a Mendelian inheritance pattern. Here we present the case of two Moroccan patients each affected by a different hereditary neurological disorder. In the first patient WES analysis revealed the presence of the p.Ser72Leu de novo mutation in the PMP22 gene reported for the first time in Africa, specifically in Morocco. This variant is predicted to be in a mutation "hot-spot" region causing Dejerine-Sottas syndrome called also Charcot-Marie-Tooth type 3. The molecular modeling study suggests an important alteration of hydrogen and hydrophobic interactions between the residue in position 72 of the PMP22 protein and its surrounding amino acids. On the other hand, the p.Ala177Thr mutation on the RNASEH2B gene, responsible of Aicardi-Goutières syndrome 2, was carried in a homozygous state by the second patient descending from a consanguineous family. This mutation is common among the Moroccan population as well as in other North African countries. The present results contributed to a better follow-up of both cases allowing better symptom management with convenient treatments.

Uses of skin biopsy for sensory and autonomic nerve assessment

Skin biopsy is a valuable diagnostic tool for small-fiber-predominant neuropathy by the quantification of intraepidermal nerve fiber density (IENFD). It has the unique advantage of being a minimally invasive procedure with the potential for longitudinal evaluation of both sensory and autonomic fibers. Unmyelinated small fibers are not otherwise quantified objectively with such a level of sensitivity as has been reported with IENFD. Recent advances include an expansion of the skin punch biopsy technique to evaluate larger myelinated fibers and mechanoreceptors, and recent work has also focused on additional methods of quantifying dermal fibers and densely innervated autonomic structures. This review discusses current work using skin biopsy for the pathologic analysis of peripheral nerve fibers in neuropathy of various causes as well as its use in clinical trials.

A chronic leg ulcer presenting with Charcot-Marie-Tooth disease and type 2 diabetes: a case report

Charcot-Marie-Tooth (CMT) disease is characterized by hereditary sensorimotor polyneuropathy with foot deformity, sensorineural hearing loss, moderate developmental delay, and gait disturbance. CMT presenting with type 2 diabetes and an ulcer has not been reported. This article reports a man who presented with the symptoms mentioned above and also with a leg ulcer and type 2 diabetes. He was diagnosed with CMT disease based on family history and genetic testing. A skin defect in the left leg had manifested for more than 1 year, and results of initial fasting plasma glucose revealed type 2 diabetes. The evolution of these manifestations, coupled with a slowly progressive weakness, numbness, muscular wasting, and sensory impairment, strongly suggested the co-occurrence of 3 different diseases in the same individual.

Genetic spectrum of hereditary neuropathies with onset in the first year of life

Early onset hereditary motor and sensory neuropathies are rare disorders encompassing congenital hypomyelinating neuropathy with disease onset in the direct post-natal period and Dejerine–Sottas neuropathy starting in infancy. The clinical spectrum, however, reaches beyond the boundaries of these two historically defined disease entities. De novo dominant mutations in PMP22, MPZ and EGR2 are known to be a typical cause of very early onset hereditary neuropathies. In addition, mutations in several other dominant and recessive genes for Charcot–Marie–Tooth disease may lead to similar phenotypes. To estimate mutation frequencies and to gain detailed insights into the genetic and phenotypic heterogeneity of early onset hereditary neuropathies, we selected a heterogeneous cohort of 77 unrelated patients who presented with symptoms of peripheral neuropathy within the first year of life. The majority of these patients were isolated in their family. We performed systematic mutation screening by means of direct sequencing of the coding regions of 11 genes: MFN2, PMP22, MPZ, EGR2, GDAP1, NEFL, FGD4, MTMR2, PRX, SBF2 and SH3TC2. In addition, screening for the Charcot–Marie–Tooth type 1A duplication on chromosome 17p11.2-12 was performed. In 35 patients (45%), mutations were identified. Mutations in MPZ, PMP22 and EGR2 were found most frequently in patients presenting with early hypotonia and breathing difficulties. The recessive genes FGD4, PRX, MTMR2, SBF2, SH3TC2 and GDAP1 were mutated in patients presenting with early foot deformities and variable delay in motor milestones after an uneventful neonatal period. Several patients displaying congenital foot deformities but an otherwise normal early development carried the Charcot–Marie–Tooth type 1A duplication. This study clearly illustrates the genetic heterogeneity underlying hereditary neuropathies with infantile onset.

Differential gene expression in chronic inflammatory demyelinating polyneuropathy (CIDP) skin biopsies

Gene expression analysis previously identified molecular markers that are up-regulated in sural nerve biopsies from patients with chronic inflammatory demyelinating polyneuropathy (CIDP). To determine whether the same or additional genes are also up-regulated in skin, we applied gene microarray profiling and quantitative real-time PCR (qPCR) analysis to skin punch biopsies from patients with CIDP and controls. Five genes, allograft inflammatory factor 1 (AIF-1), lymphatic hyaluronan receptor (LYVE-1/XLKD1), FYN binding protein (FYB), P2RY1 (purinergic receptor P2Y, G-protein-coupled, 1), and MLLT3 (myeloid/lymphoid or mixed-lineage leukemia translocated to, 3), all associated with immune cells or inflammatory processes, were elevated in punch skin biopsies from patients with CIDP as compared to normal subjects or patients with Charcot-Marie-Tooth Type 1 (CMT1). The average fold change of the 5 genes over normal expression, as determined by qPCR, was significantly elevated in skin biopsies from patients with CIDP in comparison to CMT1 or diabetic neuropathy, and similar to that seen in Lyme disease. The findings indicate the presence of inflammatory changes in the skin of patients with CIDP.

Selective Vulnerability of Peripheral Nerves in Avian Riboflavin Deficiency Demyelinating Polyneuropathy

Riboflavin (vitamin B2) deficiency in young chickens produces a demyelinating peripheral neuropathy. In this study, day-old broiler meat chickens were fed a riboflavin-deficient diet (1.8 mg/kg) and killed on posthatch days 6, 11, 16, 21, and 31, while control chickens were given a conventional diet containing 5.0 mg/kg riboflavin. Pathologic changes were found in sciatic, cervical, and lumbar spinal nerves of riboflavin-deficient chickens from day 11 onwards, characterized by endoneurial oedema, hypertrophic Schwann cells, tomacula (redundant myelin swellings), demyelination/remyelination, lipid deposition, and fibroblastic onion bulb formation. Similar changes were also found in large and medium intramuscular nerves, although they were less severe in the latter. However, by contrast, ventral and dorsal spinal nerve roots, distal intramuscular nerves, and subcutaneous nerves were normal at all time points examined. These findings demonstrate, for the first time, that riboflavin deficiency in young, rapidly growing chickens produces selective injury to peripheral nerve trunks, with relative sparing of spinal nerve roots and distal nerve branches to muscle and skin. These novel findings suggest that the response of Schwann cells in peripheral nerves with riboflavin deficiency differs because either there are subsets of these cells in, or there is variability in access of nutrients to, different sites within the nerves.

Skin biopsies in myelin-related neuropathies: bringing molecular pathology to the bedside

Skin biopsy is a minimally invasive procedure and has been used in the evaluation of non-myelinated, but not myelinated nerve fibres, in sensory neuropathies. We therefore evaluated myelinated nerves in skin biopsies from normal controls and patients with Charcot-Marie-Tooth (CMT) disease caused by mutations in myelin proteins. Light microscopy, electron microscopy and immunohistochemistry routinely identified myelinated dermal nerves in glabrous skin that appeared similar to myelinated fibres in sural and sciatic nerve. Myelin abnormalities were observed in all patients with CMT. Moreover, skin biopsies detected potential pathogenic abnormalities in the axolemmal molecular architecture previously undetected in human neuropathies. Finally, myelin gene expression at both mRNA and protein levels was evaluated by real-time PCR and immunoelectron microscopy. Peripheral myelin protein 22 (PMP22) was increased in CMT1A (PMP22 duplication) and decreased in patients with hereditary neuropathy with liability to pressure palsies (PMP22 deletion). Taken together, our data suggest that skin biopsy may in certain circumstances replace the more invasive sural nerve biopsy in the morphological and molecular evaluation of inherited and other demyelinating neuropathies.

Dejerine-Sottas' neuropathy caused by the missense mutation PMP22 Ser72Leu

OBJECTIVE

To describe a patient with the Dejerine-Sottas' syndrome due to a de novo Ser72Leu amino acid substitution in the PMP22 protein and summarize the phenotype associated with this frequent mutation.

CASE REPORT

The proband has a medical history of early onset, severe, and progressive demyelinating neuropathy, accompanied by mild ptosis and limitations of eye movements. Ulnar nerve motor conduction velocities were extremely reduced (2.6 and 2.2 m/s), and the sural nerve biopsy showed onion bulbs and thinly myelinated axons. Duplication of chromosome 17p11.2 was ruled out, and the Ser72Leu substitution was found upon sequencing the PMP22 gene.

CONCLUSION

The Ser72Leu substitution is being confirmed as the most frequent point mutation in the PMP22 gene. This 'hot spot' should be considered in the strategy of looking for point mutations in the hereditary demyelinating neuropathies.

Dejerine-Sottas disease and hereditary demyelinating polyneuropathy of infancy

Dejerine-Sottas disease (DSD) was originally described as a hypertrophic polyneuropathy characterized by onset in infancy or early childhood in patients born to unaffected parents. The clinical features included distal sensory changes with ataxia; pes cavus, at times with kyphoscoliosis; motor deficit and atrophy predominating in the distal lower limbs and progressing toward the proximal limbs following a length-dependent pattern; palpable nerve hypertrophy; and Argyll-Robertson pupils. The morphological hallmark was the extensive nerve and root hypertrophy associated with demyelination-remyelination of surviving, originally myelinated axons and profuse Schwann-cell proliferation forming onion bulbs. Wide variations in clinical manifestations of chronic demyelinating polyneuropathies of early onset in children born to unaffected parents have now been reported, with only some of the characteristics required in the original study, and at least seven genes encoding the myelin proteins P0, PMP22, the transcriptional factor EGR2, and others have been implicated. Thus, DSD is now a component of the hereditary demyelinating polyneuropathies of infancy that also include subsets of the recently individualized CMT4 neuropathies. The presumed recessive transmission of patients with DSD should be confirmed by molecular genetic analysis, which is still negative in a significant proportion of patients. The nerve biopsy can be useful in patients in whom genealogical or DNA abnormalities in favor of a genetic disorder are missing, because in a few patients with a progressive or relapsing course the diagnosis of early-onset chronic inflammatory demyelinating polyneuropathy must be considered.