Adducted thumbs: A clinical clue to genetic diagnosis

Adducted Thumb in the First Trimester of Pregnancy: An Early Clue to Prenatal Diagnosis of L1 Syndrome

A pregnant woman was revealed to have an unusual position of the fetal hand by a routine 12-week ultrasound. Bilateral adducted thumbs and a male phenotype were confirmed by another ultrasound at 14 weeks' gestation. A structural survey at 18 weeks revealed fetal hydrocephalus with severe bilateral ventriculomegaly. The pregnancy was terminated, and postnatal examination with trio exome sequencing detected a hemizygous deletion (1,511 bp in size) variant of L1CAM gene in the fetus, inherited from the mother. The fetus was diagnosed as L1 syndrome (X-linked hydrocephalus). A family study found that this was a familial mutant allele. This study demonstrates that fetal hand abnormalities can be identified in the first trimester. Adducted thumbs might indicate the maldevelopment of the fetal brain, and therefore, examination of fetal hands and fingers should be integrated into fetal anomaly scans.

History and highlights of the teratological collection in the Narrenturm, Vienna (Austria)

The collection of the Narrenturm in Vienna houses and maintains more than 50,000 objects including approximately 1200 teratological specimens; making it one of the biggest collections of specimens from human origin in Europe. The existence of this magnificent collection-representing an important resource for dysmorphology research, mostly awaiting contemporary diagnoses-is not widely known in the scientific community. Here, we show that the Narrenturm harbors a wealth of specimens with (exceptionally) rare congenital anomalies. These museums can be seen as physical repositories of human malformation, covering hundreds of years of dedicated collecting and preserving, thereby creating unique settings that can be used to expand our knowledge of developmental conditions that have to be preserved for future generations of scientists.

Adducted thumb may not be mandatory for prenatal diagnosis of X-linked hydrocephalus in early second trimester

OBJECTIVE

X-linked hydrocephalus (XLH), the most common genetic hydrocephalus, is caused by mutation of the L1 cell adhesion molecule (L1CAM). A fetus/neonate with this disorder frequently shows an adducted thumb, which has been employed as a helpful finding in the prenatal diagnosis of XLH.

MATERIALS AND METHODS

We describe a male fetus with hydrocephalus without an adducted thumb: the pregnancy was terminated at 21 weeks' gestation on the parents' request. Direct sequencing of the umbilical cord revealed L1CAM mutation, which confirmed the diagnosis of XLH.

RESULTS

Our literature review demonstrated that while an adducted thumb was observed in almost all fetuses with this disorder after 24 weeks' gestation, it was noted in only 57% (8/14) of fetuses/neonates at less than 24 weeks: it was absent in 43%.

CONCLUSION

Even if an adducted thumb is not observed, XLH should not be ruled out, especially in early gestation.

HINT1-related neuropathy in Greek patients with Charcot-Marie-Tooth disease

Autosomal recessive axonal neuropathy with neuromyotonia (ARAN-NM) is a rare hereditary neuropathy within the Charcot-Marie-Tooth disease (CMT) spectrum, linked to mutations in the histidine triad nucleotide-binding protein 1 (HINT1) gene. HINT1-related neuropathy is particularly common in selected populations from Central and Eastern Europe but rare in Western European cohorts. It has not been investigated to date in the Greek population. We presently investigated the frequency of HINT1-neuropathy in a selected cohort of 42 Greek index patients with autosomal recessive or sporadic axonal hereditary neuropathy according to standard molecular genetics procedures. We identified 4 patients with biallelic mutations in HINT1, comprising 9.5% of all cases and 44.4% of cases also displaying neuromyotonia. The c.110G> C (p.Arg37Pro) HINT1 mutation was present in all cases (2 homozygous) and the c.250T> C (p.Cys84Arg) in 2 cases (compound heterozygous). HINT1-related neuropathy patients were characterized by early onset and neuromyotonia. Two patients had noteworthy clinical features, one case developing myoclonic epilepsy and the other displaying "adducted thumbs." We conclude that HINT1-related neuropathy is common in selected Greek patients with hereditary neuropathy within the CMT spectrum, in accordance with some, but not all, European populations.

Characteristic clinical and ultrastructural findings in nesprinopathies

AIMS

To define the neurological and neuropathological alterations caused by SYNE1 mutations.

METHODS

We describe 5 patients (3 males, 2 females; age 3-24 years) from 3 families. The diagnostic work-up included three muscle biopsies and two nerve biopsies in three of the cases.

RESULTS

Three different phenotypes were discerned. Two patients showed progressive ataxia, mental retardation, neuropathy and radially deviated thumbs (spinocerebellar ataxia, SCAR, type 8 phenotype). Two patients had mild congenital myopathy with restrictive lung disease, clubfeet and thumb anomalies (myopathic arthrogryposis). One patient had congenital myopathy with dilated cardiomyopathy and adducted thumbs (Emery-Dreifuss Muscular Dystrophy, EDMD, type 4). Light microscopy of the three muscle biopsies revealed chronic non-necrotizing myopathy without rimmed vacuoles in all cases combined with neurogenic atrophy in one case. The two nerve biopsies showed predominantly axonal neuropathy with demyelinating features. Nuclear alterations, most notably lobulation and focal widening of the space between inner and outer leaflet of the nuclear envelope, were a prominent consistent feature of myonuclei and Schwann cell nuclei in each of the three muscle specimens and one nerve specimen that could be examined by electron microscopy.

CONCLUSION

Thumb abnormalities and nuclear envelope alterations are characteristic for SYNE 1 mutations. Schwann cell nuclei are affected, indicating that such nuclear envelope changes in glial cells contribute to the neurodegenerative phenotype in human nesprinopathies.

Adducted thumb as an isolated morphologic finding: an early sonographic sign of impaired neurodevelopment: A STROBE compliant study

Fetal adducted thumbs have been described in association with hydrocephalus and other abnormalities, but in cases without other structural malformations the determination of prognosis and recurrence risk is challenging. The aim of our study is to analyze the characteristics, natural history, and postnatal outcome of such cases.A retrospective study was conducted over a period of 4 years in a tertiary referral center. All fetuses diagnosed as adducted thumbs without other structural malformations comprised the study group. Prenatal sonographic features and neonatal outcome are documented.There were 4 cases of fetal adducted thumbs diagnosed during the study period. No cases demonstrated other structural malformations throughout the gestation. A smaller head was noted in 2 cases during the follow-up, and all cases presented with polyhydramnios on the first or ensuing scans. Three cases died after birth due to swallowing or breathing difficulty, and the surviving 1 showed convulsion and mental retardation.Fetal adducted thumb might be an early and specific sonographic marker of impaired neurodevelopment. Close follow-up and genetic investigation should be performed in these cases. Ultrasound examination plays an important role in the prenatal diagnosis and counseling of cases without detailed prenatal genetic analysis.

Three cases with L1 syndrome and two novel mutations in the L1CAM gene

Mutations in the L1CAM gene have been identified in the following various X-linked neurological disorders: congenital hydrocephalus; mental retardation, aphasia, shuffling gait, and adducted thumbs (MASA) syndrome; spastic paraplegia; and agenesis of the corpus callosum. These conditions are currently considered different phenotypes of a single entity known as L1 syndrome. We present three families with L1 syndrome. Sequencing of the L1CAM gene allowed the identification of the following mutations involved: a known splicing mutation (c.3531-12G>A) and two novel ones: a missense mutation (c.1754A>C; p.Asp585Ala) and a nonsense mutation (c.3478C>T; p.Gln1160Stop). The number of affected males and carrier females identified in a relatively small population suggests that L1 syndrome may be under-diagnosed.

CONCLUSION

L1 syndrome should be considered in the differential diagnosis of intellectual disability or mental retardation in children, especially when other signs such as hydrocephalus or adducted thumbs are present.

Prenatal Three-Dimensional Ultrasound Detection of Adducted Thumbs in X-Linked Hydrocephaly: Two Case Reports with Molecular Genetic Studies

X-linked hydrocephaly is a rare sex-linked genetic recessive condition occurring in 1/30,000 deliveries. Adduction of thumbs and mental retardation are additional associated clinical findings. We describe two cases of X-linked hydrocephaly with associated adducted thumbs that were diagnosed prenatally with the combined use of three-dimensional (3D) ultrasound and fetal blood sampling for cytogenetic and molecular analyses. This report suggests that 3D ultrasound can facilitate the identification of adducted thumbs in fetuses affected by X-linked hydrocephaly and supports evaluation of the fetal hands as an integral part of the ultrasound anatomical assessment in male fetuses with hydrocephaly secondary to aqueductal stenosis.