A case of decapitated spermatozoa in an infertile man

Semen parameters are seriously affected in acephalic spermatozoa syndrome

BACKGROUND

Previous studies have reported that some patients with headless spermatozoa have poor semen quality, but there has been no published systematic analysis of semen quality in patients with different proportions of headless spermatozoa in semen. We aimed to explore the association of acephalic spermatozoa syndrome and semen quality in men with distinct proportions of headless spermatozoa.

MATERIAL AND METHODS

Semen parameter values in patients for whom headless spermatozoa were found in the ejaculates was studied and compared to that of 413 age-matched prenatal examination patients. All semen samples were analyzed following the same methodology in a single laboratory.

RESULTS

All semen parameter values except semen volume were negatively (P < 0.05) correlated with the proportion of headless spermatozoa. The semen samples were divided into four groups on the basis of the proportion of headless spermatozoa (PHS) as follows: 0 < PHS ≤ 5% (n = 172, Group A1); 5 < PHS ≤ 10% (n = 76, Group A2); 10 < PHS ≤ 20% (n = 71, Group B); and PHS > 20% (n = 71, Group C). In Group A1, only one semen parameter value (progressive motility) was lower than those of the control group, but in Group A2, this increased to five (sperm vitality, normal sperm morphology, sperm motility, VCL (curvilinear velocity) and ALH (amplitude of lateral head displacement)). Worse still, all semen parameter values were significantly lower in Group B and Group C than in the control group (P < 0.05).

CONCLUSIONS

Semen samples containing headless spermatozoa tend to have lower quality than samples without headless spermatozoa. Increases in the proportion of headless spermatozoa in semen are associated with decreased semen quality. We suggest that headless spermatozoa should be seriously assessed and accurately counted in semen analysis, especially for ejaculate in which the proportion of headless spermatozoa exceeds 5%.

Genetic basis of acephalic spermatozoa syndrome, and intracytoplasmic sperm injection outcomes in infertile men: a systematic scoping review

PURPOSE

Acephalic spermatozoa syndrome (ASS) is known as a severe type of teratozoospermia, defined as semen composed of mostly headless spermatozoa that affect male fertility. In this regard, this systematic review aimed to discuss gene variants associated with acephalic spermatozoa phenotype as well as the clinical outcomes of intracytoplasmic sperm injection (ICSI) treatment for the acephalic spermatozoa-associated male infertility.

METHODS

A systematic search was performed on PubMed, Embase, Scopus, and Ovid databases until May 17, 2020. This systematic scoping review was reported in terms of the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) statement.

RESULTS

Twenty articles were included in this systematic review. Whole-exome and Sanger sequencing have helped in the identification of variants in SUN5, PMFBP1, BRDT, TSGA10, DNAH6, HOOK1, and CEP112 genes as possible causes of this phenotype in humans. The results of the ICSI are conflicting due to both positive and negative reports of ICSI outcomes.

CONCLUSION

ASS has a genetic origin, and several genetic alterations related to the pathogenesis of this anomaly have been recently identified. Notably, only SUN5 and PMFBP1 mutations are well-known to be implicated in ASS. Accordingly, more functional studies are needed to confirm the pathogenicity of other variants. ICSI could provide a promising treatment for acephalic spermatozoa-associated male infertility. Besides the importance of sperm head-tail junction integrity, some other factors, whether within the sperm cell or female factors, may be involved in the ICSI outcome.

Beyond Acephalic Spermatozoa: The Complexity of Intracytoplasmic Sperm Injection Outcomes

This review analyses the genetic mechanisms of acephalic spermatozoa (AS) defects, which are associated with primary infertility in men. Several target genes of headless sperms have been identified but intracytoplasmic sperm injection (ICSI) outcomes are complex. Based on electron microscopic observations, broken points of the sperm neck are AS defects that are based on various genes that can be classified into three subtypes: HOOK1, SUN5, and PMFBP1 genes of subtype II; TSGA10 and BRDT genes of subgroup III, while the genetic mechanism(s) and aetiology of AS defects of subtype I have not been described and remain to be explored. Interestingly, all AS sperm of subtype II achieved better ICSI outcomes than other subtypes, resulting in clinical pregnancies and live births. For subtype III, the failure of clinical pregnancy can be explained by the defects of paternal centrioles that arrest embryonic development; for subtype I, this was due to a lack of a distal centriole. Consequently, the embryo quality and potential ICSI results of AS defects can be predicted by the subtypes of AS defects. However, this conclusion with regard to ICSI outcomes based on subtypes still needs further research, while the existence of quality of oocyte and implantation failure in women cannot be ignored.

Odf2 haploinsufficiency causes a new type of decapitated and decaudated spermatozoa, Odf2-DDS, in mice

Outer dense fibre 2 (Odf2 or ODF2) is a cytoskeletal protein required for flagella (tail)-beating and stability to transport sperm cells from testes to the eggs. There are infertile males, including human patients, who have a high percentage of decapitated and decaudated spermatozoa (DDS), whose semen contains abnormal spermatozoa with tailless heads and headless tails due to head-neck separation. DDS is untreatable in reproductive medicine. We report for the first time a new type of Odf2-DDS in heterozygous mutant Odf2+/- mice. Odf2+/- males were infertile due to haploinsufficiency caused by heterozygous deletion of the Odf2 gene, encoding the Odf2 proteins. Odf2 haploinsufficiency induced sperm neck-midpiece separation, a new type of head-tail separation, leading to the generation of headneck sperm cells or headnecks composed of heads with necks and neckless tails composed of only the main parts of tails. The headnecks were immotile but alive and capable of producing offspring by intracytoplasmic headneck sperm injection (ICSI). The neckless tails were motile and could induce capacitation but had no significant forward motility. Further studies are necessary to show that ICSI in humans, using headneck sperm cells, is viable and could be an alternative for infertile patients suffering from Odf2-DDS.

The functional anatomy of the human spermatozoon: relating ultrastructure and function

The Internet, magazine articles, and even biomedical journal articles, are full of cartoons of spermatozoa that bear minimal resemblance to real spermatozoa, especially human spermatozoa, and this had led to many misconceptions about what spermatozoa look like and how they are constituted. This review summarizes the historical and current state of knowledge of mammalian sperm ultrastructure, with particular emphasis on and relevance to human spermatozoa, combining information obtained from a variety of electron microscopic (EM) techniques. Available information on the composition and configuration of the various ultrastructural components of the spermatozoon has been related to their mechanistic purpose and roles in the primary aspects of sperm function and fertilization: motility, hyperactivation, capacitation, the acrosome reaction and sperm-oocyte fusion.

Deficiency in Outer Dense Fiber 1 Is a Marker and Potential Driver of Idiopathic Male Infertility

Globally, ∼1 in 15 men of reproductive age are infertile, yet the precise mechanisms underlying their gamete failure are unknown. Although a semen analysis is performed to determine fertilizing potential, the diagnostic suitability of this analysis has been questioned in several reports, as many men, classified as infertile according to their semen analysis, subsequently turn out to be fertile. Herein, we have used a quantitative (phospho)-proteomic analysis, using enrichment on titanium dioxide followed by ion-trap mass spectrometry (LC-MS/MS), to compare the semen of infertile versus fertile males. One protein, namely outer dense fiber 1 (ODF1), was dramatically reduced in infertile males. Using specific antibodies, we then screened the gametes of a cohort of suspected infertile men and demonstrated a reduction in the amount of ODF1 compared with fertile controls. Stress treatment of sperm deficient in ODF1 caused the head to decapitate, suggesting why these gametes fail to initiate fertilization. Interestingly, electron micrographs of ODF1-deficient spermatozoa revealed an abnormal connecting piece, indicating several developmental defects with both the implantation plate and the thin laminated fibers. In some cases, the implantation plate appeared to be reduced in size or was overburdened by granular material near the connecting piece. Hence, a strong reduction ODF1 is a marker of idiopathic male infertility and a potential driver of this condition.

Headless spermatozoa in infertile men

Spermatozoa morphology, an important parameter in a semen specimen's potential fertility evaluation, is a significant factor for in vitro fertilisation in assisted reproductive technology. Eleven sterile men with headless spermatozoa, a type of human teratozoospermia, are presented. Their ejaculates' headless spermatozoa percentages were high with rare normal spermatozoa forms. Additionally, abnormal morphology (e.g. round-headed or microcephalic spermatozoa) was also found. Spermatozoa motility was somewhat affected, potentially because of the missing mitochondrial sheath at the sperm tail base. Patients who underwent assisted reproductive technology treatment experienced adverse pregnancy outcomes. Work types and corresponding environments seemed irrelevant, but specific family history may have prompted its genetic origin. Computer-assisted semen analysis systems easily mistake headless spermatozoa as oligozoospermia because of nonrecognition of the loose head. However, morphological testing, especially with an electronic microscope, clearly identifies abnormal spermatozoa. Future exploration requires more methods investigating the frequency and percentage of this morphological abnormality in different populations with varied fertility levels. Such research would estimate the probable correlation of the abnormality with other semen parameters and examine the potential developmental or genetic origins. During clinical work, medical staff should detect these cases, avoid misdiagnosis and provide proper consultation about diagnosis and assisted reproductive technology treatment.

Biallelic SUN5 Mutations Cause Autosomal-Recessive Acephalic Spermatozoa Syndrome

Acephalic spermatozoa syndrome is a rare and severe form of teratozoospermia characterized by a predominance of headless spermatozoa in the ejaculate. Family clustering and consanguinity suggest a genetic origin; however, causative mutations have yet to be identified. We performed whole-exome sequencing in two unrelated infertile men and subsequent variant filtering identified one homozygous (c.824C>T [p.Thr275Met]) and one compound heterozygous (c.1006C>T [p.Arg356Cys] and c.485T>A [p.Met162Lys]) SUN5 (also named TSARG4) variants. Sanger sequencing of SUN5 in 15 additional unrelated infertile men revealed four compound heterozygous (c.381delA [p.Val128Serfs^∗7] and c.824C>T [p.Thr275Met]; c.381delA [p.Val128Serfs^∗7] and c.781G>A [p.Val261Met]; c.216G>A [p.Trp72^∗] and c.1043A>T [p.Asn348Ile]; c.425+1G>A/c.1043A>T [p.Asn348Ile]) and two homozygous (c.851C>G [p.Ser284^∗]; c.350G>A [p.Gly114Arg]) variants in six individuals. These 10 SUN5 variants were found in 8 of 17 unrelated men, explaining the genetic defect in 47.06% of the affected individuals in our cohort. These variants were absent in 100 fertile population-matched control individuals. SUN5 variants lead to absent, significantly reduced, or truncated SUN5, and certain variants altered SUN5 distribution in the head-tail junction of the sperm. In summary, these results demonstrate that biallelic SUN5 mutations cause male infertility due to autosomal-recessive acephalic spermatozoa syndrome.

Evaluation of sperm nuclear integrity in patients with different percentages of decapitated sperm in ejaculates

The decapitated sperm defect is a rare type of teratozoospermia responsible for male infertility. Spermatozoa from patients affected by this syndrome are used for intracytoplasmic sperm injection (ICSI) although little is known about their DNA integrity. This study evaluated sperm nuclear alterations in four patients and ten fertile men (control group). Sperm samples were examined by light, transmission electron and high-magnification contrast microscopy and analysed after terminal deoxynucleotidyltransferase-mediated dUTP nick end labelling, aniline blue staining and fluorescence in-situ hybridization. Spermatozoa from patients presented varying degrees of decapitation, along with morphological and ultrastructural head abnormalities. Whereas the proportion of spermatozoa with fragmented DNA and numerical chromosome abnormalities was similar in patients 1-3 and controls, the percentage of spermatozoa with hypocondensed chromatin was higher in patients 1-3 than in fertile men. Patient 4 presented a distinct phenotype, with an increased proportion of flagellated spermatozoa with DNA strand breaks as well as increased aneuploidy and diploidy rates compared with controls and with patients 1-3. No successful pregnancy resulted from ICSI although embryos were obtained for three patients. The morphological defects and the nuclear alterations observed in spermatozoa of patients with the decapitated sperm syndrome may have contributed to ICSI failures.

Spata6 is required for normal assembly of the sperm connecting piece and tight head-tail conjunction

"Pinhead sperm," or "acephalic sperm," a type of human teratozoospermia, refers to the condition in which ejaculate contains mostly sperm flagella without heads. Family clustering and homogeneity of this syndrome suggests a genetic basis, but the causative genes remain largely unknown. Here we report that Spata6, an evolutionarily conserved testis-specific gene, encodes a protein required for formation of the segmented columns and the capitulum, two major structures of the sperm connecting piece essential for linking the developing flagellum to the head during late spermiogenesis. Inactivation of Spata6 in mice leads to acephalic spermatozoa and male sterility. Our proteomic analyses reveal that SPATA6 is involved in myosin-based microfilament transport through interaction with myosin subunits (e.g., MYL6).

AF-2364 is a prospective spermicide candidate

AbstractInhibition of sperm motility has recently become a promising target for male contraceptive development. AF-2364, an analogue of Lonidamine (LND), had a contraceptive effect when orally administered to adult Sprague-Dawley rats. LND can also target mitochondria to inhibit oxygen consumption and block energy metabolism in tumour cells. However, there are no reports of the effects of AF-2364 on human sperm function. Herein we describe the action of AF-2364 on human sperm in vitro, as well as the mechanisms involved. AF-2364 specifically blocked human sperm motility in vitro. Further experiments revealed that AF-2364 can target sperm mitochondrial permeability transition (MPT) pores to induce the loss of sperm mitochondrial membrane potential (DeltaPsim) and decrease ATP generation; however, no significant changes in the cytoskeletal network or the human sperm proteome were detected after exposure to AF-2364. Incubation of AF-2364 with other human or mouse cell lines indicated that the spermicidal effect at the lower concentration was specific. In summary, the spermicidal effect of AF-2364 involves direct action on sperm MPT pores, and this compound should be further investigated as a new spermicide candidate.

RIM-BP3 is a manchette-associated protein essential for spermiogenesis

During spermiogenesis, round spermatids are converted into motile sperm in mammals. The mechanisms responsible for sperm morphogenesis are poorly understood. We have characterized a novel protein, RIM-BP3, with a specialized function in spermatid development in mice. The RIM-BP3 protein is associated with the manchette, a transient microtubular structure believed to be important for morphogenesis during spermiogenesis. Targeted deletion of the RIM-BP3 gene resulted in male infertility owing to abnormal sperm heads, which are characterized by a deformed nucleus and a detached acrosome. Consistent with its role in morphogenesis, the RIM-BP3 protein physically associates with Hook1, a known manchette-bound protein required for sperm head morphogenesis. Interestingly, RIM-BP3 does not interact with the truncated Hook1 protein characterized in azh (abnormal spermatozoon head) mutant mice. Moreover, RIM-BP3 and Hook1 mutant mice display several common abnormalities, in particular with regard to the ectopic positioning of the manchette within the spermatid, a presumed cause of sperm head deformities. These observations suggest an essential role for RIM-BP3 in manchette development and function through its interaction with Hook1. As the occurrence of deformed spermatids is one of the common abnormalities leading to malfunctional sperm, identification of RIM-BP3 might provide insight into the molecular cue underlying causes of male infertility in humans.

The role of the mitochondrion in sperm function: is there a place for oxidative phosphorylation or is this a purely glycolytic process?

We review here the current knowledge related to the metabolic pathways used by spermatozoa to meet their high demands for ATP. This is discussed with special emphasis on one of their key roles, motility. We believe that the controversy among glycolytic and oxidative phosphorylation supporters is artificial and, as it happens in many other cell types, the source of ATP is multiple and depends on external inputs.

Pregnancy from intracytoplasmic sperm injection of a sperm head and detached tail

OBJECTIVE

To evaluate sperm ultrastructure and the efficacy of intracytoplasmic sperm injection (ICSI) with careful positioning of the sperm midpiece next to the sperm head in a patient with easily decapitated sperm syndrome.

DESIGN

In vitro fertilization case report with retrospective sperm ultrastructure analysis.

SETTING

In vitro fertilization clinic and andrology laboratory.

PATIENT(S)

A couple seeking treatment for diminished ovarian reserve and male factor infertility using donor oocyte IVF.

INTERVENTION(S)

Motile sperm inadvertently decapitated during micromanipulation were used for a modified ICSI procedure in which the midpiece was carefully positioned proximal to the sperm head. Sperm were also analyzed by transmission electron microscopy (TEM).

MAIN OUTCOME MEASURE(S)

Fertilization rate, embryo development, pregnancy, and the incidence of normal sperm ultrastructure.

RESULT(S)

The ICSI resulted in a fertilization rate of 63% and embryo development of good to moderate quality of 36% of the embryos. Transfer of two embryos resulted in a pregnancy and birth of a healthy child. Normal sperm centrosomes were identified retrospectively.

CONCLUSION(S)

Pregnancy can result in patients where the sperm are decapitated during immobilization before ICSI if normal centrosomes are present and the head and midpiece are positioned closely together.

Stage-specific expression of mouse germ cell-less-1 (mGCL-1), and multiple deformations during mgcl-1 deficient spermatogenesis leading to reduced fertility

A mouse homologue of Drosophila germ cell-less, mouse germ cell-less-1 (mgcl-1), is highly expressed in the testis. Previous report revealed that the fertility of the mgcl-1(-/-) male mice is reduced significantly as a result of various morphological abnormalities in the sperm (Kimura et al., 2003). To elucidate the function of mgcl-1 in spermatogenesis, the expression of mGCL-1 in the wild-type testis was examined. Immunohistochemical studies demonstrated that mGCL-1 first appeared in the nuclei of the pachytene spermatocytes at stage VI of the seminiferous epithelium, and existed in those of spermatids until step 8 during spermatogenesis. mGCL-1 was not detectable after step 9 spermatids. The testicular cells and epididymal sperm were further analyzed morphologically using mgcl-1(-/-) mice. In the testis, deformed nuclei first occurred in the pachytene spermatocytes at stage VI, which is consistent with the time of the first appearance of the mGCL-1 protein in the wild-type testis. Abnormal nuclei and acrosomes were found in spermatids after step 5, and nuclei of the spermatids and epididymal sperm were frequently invaginated. In addition, variously deformed sperm such as bent-neck, multi-headed or multi-nucleated sperm were observed in the mgcl-1(-/-) cauda epididymidis. However, several key structures such as the acroplaxome marginal ring (Kierszenbaum et al., 2003), postacrosomal sheath, and posterior ring apparently formed. In addition, MN7 and MN13, essential substances for fertilization that are located in sperm heads, were detectable in the mgcl-1 null sperm. These observations provide important insights into the mechanisms regulating the nuclear architecture and causes of human infertility.

Morphological abnormalities in the spermatozoa of fertile and infertile men

The morphological analysis of the spermatozoa from fertile and infertile men was performed using light and electron microscopy to clarify the relationship between sperm morphology and fertility. Semen samples obtained from 22 partners of pregnant women were prepared according to the protocol standardized in an international collaborative study. Semen samples from 17 patients with asthenozoospermia or varicocele were collected in a hospital. Abnormalities in the spermatozoa were classified into three types for the tails, two for the midpieces, and six for the heads according to the criteria adapted from WHO guidelines (World Health Organization, 1999: WHO laboratory manual for the examination of human semen and semen-cervical mucus interaction (4th edition)). Approximately 14% of the spermatozoa from the fertile men had abnormal tails at the light microscopic level while approximately 44% had abnormal heads. Most types of abnormalities found in the spermatozoa from the asthenozoospermic and varicocele patients were encountered in those from the fertile men, although the semen from the fertile men contained a higher percentage of normal spermatozoa than that from the patients. These results were also confirmed at the ultrastructural level. Most abnormal cell types are encountered in semen from fertile men, although the incidence of abnormalities is low.

Decapitated and decaudated spermatozoa in man, and pathogenesis based on the ultrastructure

The ultrastructure of decapitated tails and decaudated heads of ejaculated spermatozoa from an infertile man were investigated. The decaudated heads had the nucleus and acrosome, but neither the implantation fossa nor the basal plate were observed at the caudal pole of the nucleus. The nuclear membrane at this portion showed numerous nuclear pores. The decapitated tails contained the proximal centriole at the proximal end. In addition, most decapitated tails had segmented columns, outer coarse fibres, axoneme, mitochondrial sheath and fibrous sheath in the normal position. The ultrastructure reflects the high motility of the decapitated tails of the spermatozoa. Drastic abnormalities were found in the developing spermatids in the biopsied testes. In spermatids later than the Golgi phase, the pair of centrioles were floating in the cytoplasm of the spermatid, but the distal centriole elongated the flagellum. Neither the implantation fossa nor the basal plate were observed at the caudal pole of the nucleus. It is concluded that the tail might be separated from the head before or after completion of tail formation in spermatids. The explanation for why the proximal centriole failed to connect to the nucleus is unknown.

Easily decapitated spermatozoa defect: a possible cause of unexplained infertility

We report the first 16 cases of a new sperm abnormality which we call 'easily decapitated spermatozoa defect'. This was discovered during intracytoplasmic sperm injection (ICSI) in couples with unexplained infertility. Semen analysis was normal, but minimal micromanipulation for ICSI resulted in decapitation of the spermatozoon during immobilization. For some oocytes the head and tail were injected separately, in others the intact sperm was injected after minimal immobilization. A fertilization rate of 47.5% was obtained using ICSI. Conventional in-vitro fertilization (IVF) on sibling oocytes (three cases) or in a previous cycle (three cases) resulted in total failure of fertilization. All patients reached the embryo transfer stage and three pregnancies resulted. Findings on electron microscopy in four cases included spermatozoa with degeneration or absence of the basal plate, abnormalities of the proximal centriole and degeneration of the midpiece with a large cytoplasmic droplet. We conclude that an occult sperm abnormality presenting as easily decapitated spermatozoa during ICSI could be a cause of unexplained infertility, as it resulted in total failure of fertilization in conventional IVF. Further research is necessary to investigate this sperm abnormality.

Failure of pregnancy after intracytoplasmic sperm injection with decapitated spermatozoa: case report

The case of a couple with a history of long standing primary infertility is reported in which the man presented with a decapitated sperm defect. The woman had a normal history and presented with normal clinical characteristics. The couple underwent one unsuccessful conventional in-vitro fertilization (IVF). Subsequently, embryos were obtained and transferred after assisted fertilization attempts: in all, three subzonal inseminations and four intracytoplasmic sperm injections. A total of 49 mature oocytes was injected in both studies, 25 embryos obtained and 20 embryos transferred, three of them after freezing and thawing. Despite the good embryo morphology, implantation was unsuccessful and no pregnancy occurred. The failure of implantation may have resulted from an arrest in early embryonic development related to the sperm anomaly. One hypothesis is that transferred embryos may carry a chromosomal imbalance that prevents them from progressing to the blastocyst stage. Nevertheless, we cannot exclude the possibility that the woman is responsible for the implantation failure. Co-culture associated with a further attempt could provide information regarding the ability of embryos to progress to the blastocyst stage and implant.

Ultrastructural features and pathogenesis of decapitated spermatozoa in a boar

A boar with decapitated spermatozoa was examined. The growth rate and libido were normal. The right testis was in the scrotum, but the left one was intra-abdominal. Ejaculated spermatozoa and tissue specimen from both testes were observed by light and electron microscopy. Only tailless heads and headless tails of spermatozoa were observed in the ejaculate. The ratio of heads to tails was about 1:4. Motility of the headless tails was about 25%. The proximal extremity in the tail was occupied by the proximal centriole. The basal plate could not be found in the head or in the tail. Pathogenesis of decapitated spermatozoa in the present case was analysed by investigating spermiogenesis in the scrotal testis. Since the pair of centrioles failed to approach the nucleus, mechanical connection between the proximal centriole and the nucleus did not seem to be established. In addition, the basal plate was not formed on the nuclear membrane. Since the ratio of tailless heads to headless tails was also 1:4 in the testis, it was concluded that the heads had already detached the tails in the testis.

A case of an infertile man with short-tailed spermatozoa

Ejaculated spermatozoa from an infertile patient were examined by scanning and transmission electron microscopy. All spermatozoa had abnormalities in the tail region. The abnormalities were divided into three types: (a) spermatozoa with a spherical tail. The tail was larger than the head in volume. This type of abnormality accounted for about 60% of the population; (b) spermatozoa with a blunt tail. The tails were about 2 microns in diameter and about 7 microns in length. This type of abnormality accounted for about 30% of the population of an ejaculate; (c) spermatozoa without a tail. Some of these had only a rudimentary tail. About 10% of the population belonged to this type. In types A and B, all components of the tail, except for dynein arms, were observed, but they were severely disarranged. Biopsy specimens of the testes and of the nasal mucosa of this patient were also investigated. The testicular biopsy showed defects in manchette formation. Normal development of the manchette could not be observed. The nasal epithelium showed absence of the inner dynein arms in the cilia.