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Distal monosomy 10q
Distal monosomy 10q is a chromosomal anomaly involving terminal deletion of the long arm of chromosome 10 and is characterized by facial dysmorphism, pre- and postnatal growth retardation, cardiac and genital anomalies, and developmental delay.
Prevalence is unknown but around 40 cases have been described in the literature so far.
There is no specific clinical feature associated with this chromosome anomaly. Craniofacial features include hypertelorism, strabismus, a prominent or broad nasal bridge, and posteriorly rotated low-set ears. Hypotonia is frequent, and limited joint extensions and early scoliosis have been reported in a few cases. Cardiac defects are not a constant finding and vary to include patent ductus arteriosus, ventricular septal defect, tetralogy of Fallot and truncus arteriosus (see these terms). Genital abnormalities have been mostly reported in males and include undescended testis, micropenis and a posterior urethral valve. Bladder distension due to cervical dysfunction may occur in females and may be evident during the antenatal period. Severe genital abnormalities (ambiguous external genitalia) have been reported in a few cases. Psychomotor retardation (generally described as mild) was present in all reported cases.
Distal monosomy 10q results from a subterminal 10q deletion with breakpoints in the 10q25 or 10q26 band leading to partial monosomy for the genes located in this area. Most of the reported cases involved de novo terminal deletions resulting from abnormal non-allelic homolog recombination during meiosis.
Diagnosis is made by molecular analysis. Comparative genomic hybridization (CGH) microarray or subterminal chromosome multiplex ligation-dependent probe amplification (MLPA) may be necessary since conventional cytogenetic analysis may not be sensitive enough to detect very short subterminal deletions.
Antenatal molecular testing for the presence of a subterminal 10q deletion may be proposed in case of suspicion of a posterior urethral valve in males (associated or not with genital abnormalities) or in case of bladder distension in female fetuses. The risk of recurrence is low but prenatal screening for chromosomal abnormalities must be proposed, with the use of FISH markers for the 10q subterminal region.
Management and treatment
Management is symptomatic only. Bladder dysfunction may require transient cystostomy. Special education programs to improve cognitive development are needed in most cases.
The prognosis is unclear as there are no available data concerning long-term follow up, especially up until adult age.